One document matched: draft-ietf-rohc-rfc3095bis-rohcv2-profiles-02.txt
Differences from draft-ietf-rohc-rfc3095bis-rohcv2-profiles-01.txt
Robust Header Compression G. Pelletier
Internet-Draft K. Sandlund
Intended status: Standards Track Ericsson
Expires: April 4, 2008 October 2, 2007
RObust Header Compression Version 2 (ROHCv2): Profiles for RTP, UDP, IP,
ESP and UDP Lite
draft-ietf-rohc-rfc3095bis-rohcv2-profiles-02
Status of this Memo
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Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
This document specifies ROHC (Robust Header Compression) profiles
that efficiently compress RTP/UDP/IP (Real-Time Transport Protocol,
User Datagram Protocol, Internet Protocol), RTP/UDP-Lite/IP (User
Datagram Protocol Lite), UDP/IP, UDP-Lite/IP, IP and ESP/IP
(Encapsulating Security Payload) headers.
This specification defines a second version of the profiles found in
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RFC 3095, RFC 3843 and RFC 4019; it supersedes their definition, but
does not obsolete them.
The ROHCv2 profiles introduce a number of simplifications to the
rules and algorithms that govern the behavior of the compression
endpoints. It also defines robustness mechanisms that may be used by
a compressor implementation to increase the probability of
decompression success when packets can be lost and/or reordered on
the ROHC channel. Finally, the ROHCv2 profiles define its own
specific set of packet formats, using the ROHC formal notation.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Background (Informative) . . . . . . . . . . . . . . . . . . 7
4.1. Classification of header fields . . . . . . . . . . . . . 7
4.2. Improvements of ROHCv2 over RFC3095 profiles . . . . . . 8
4.3. Operational Characteristics of ROHCv2 Profiles . . . . . 10
5. Overview of the ROHCv2 Profiles (Informative) . . . . . . . . 10
5.1. Compressor Concepts . . . . . . . . . . . . . . . . . . . 11
5.1.1. Optimistic Approach . . . . . . . . . . . . . . . . . 11
5.1.2. Tradeoff between robustness to losses and to
reordering . . . . . . . . . . . . . . . . . . . . . 11
5.1.3. Interactions with the Decompressor Context . . . . . 13
5.2. Decompressor Concepts . . . . . . . . . . . . . . . . . . 14
5.2.1. Decompressor State Machine . . . . . . . . . . . . . 14
5.2.2. Decompressor Context Management . . . . . . . . . . . 17
5.2.3. Feedback logic . . . . . . . . . . . . . . . . . . . 19
6. ROHCv2 Profiles (Normative) . . . . . . . . . . . . . . . . . 19
6.1. Channel Parameters, Segmentation and Reordering . . . . . 19
6.2. Profile Operation, per-context . . . . . . . . . . . . . 19
6.3. Control Fields . . . . . . . . . . . . . . . . . . . . . 20
6.3.1. Master Sequence Number (MSN) . . . . . . . . . . . . 21
6.3.2. Reordering Ratio . . . . . . . . . . . . . . . . . . 21
6.3.3. IP-ID behavior . . . . . . . . . . . . . . . . . . . 21
6.3.4. UDP-Lite Coverage Behavior . . . . . . . . . . . . . 22
6.3.5. Timestamp Stride . . . . . . . . . . . . . . . . . . 22
6.3.6. Time Stride . . . . . . . . . . . . . . . . . . . . . 22
6.3.7. CRC-3 for Control Fields . . . . . . . . . . . . . . 22
6.4. Reconstruction and Verification . . . . . . . . . . . . . 23
6.5. Compressed Header Chains . . . . . . . . . . . . . . . . 23
6.6. Packet Formats and Encoding Methods . . . . . . . . . . . 25
6.6.1. baseheader_extension_headers . . . . . . . . . . . . 25
6.6.2. baseheader_outer_headers . . . . . . . . . . . . . . 25
6.6.3. inferred_udp_length . . . . . . . . . . . . . . . . . 25
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6.6.4. inferred_ip_v4_header_checksum . . . . . . . . . . . 26
6.6.5. inferred_mine_header_checksum . . . . . . . . . . . . 26
6.6.6. inferred_ip_v4_length . . . . . . . . . . . . . . . . 27
6.6.7. inferred_ip_v6_length . . . . . . . . . . . . . . . . 27
6.6.8. Scaled RTP Timestamp Encoding . . . . . . . . . . . . 28
6.6.9. timer_based_lsb . . . . . . . . . . . . . . . . . . . 29
6.6.10. inferred_scaled_field . . . . . . . . . . . . . . . . 30
6.6.11. control_crc3_encoding . . . . . . . . . . . . . . . . 31
6.6.12. inferred_sequential_ip_id . . . . . . . . . . . . . . 32
6.6.13. list_csrc(cc_value) . . . . . . . . . . . . . . . . . 32
6.7. Encoding Methods With External Parameters . . . . . . . . 36
6.8. Packet Formats . . . . . . . . . . . . . . . . . . . . . 39
6.8.1. Initialization and Refresh Packet (IR) . . . . . . . 39
6.8.2. Compressed Packet Formats (CO) . . . . . . . . . . . 40
6.9. Feedback Formats and Options . . . . . . . . . . . . . . 99
6.9.1. Feedback Formats . . . . . . . . . . . . . . . . . . 99
6.9.2. Feedback Options . . . . . . . . . . . . . . . . . . 101
7. Security Considerations . . . . . . . . . . . . . . . . . . . 103
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 103
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 104
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 105
10.1. Normative References . . . . . . . . . . . . . . . . . . 105
10.2. Informative References . . . . . . . . . . . . . . . . . 106
Appendix A. Detailed classification of header fields . . . . . 106
Appendix A.1. IPv4 Header Fields . . . . . . . . . . . . . . . . 107
Appendix A.2. IPv6 Header Fields . . . . . . . . . . . . . . . . 109
Appendix A.3. UDP Header Fields . . . . . . . . . . . . . . . . 111
Appendix A.4. UDP-Lite Header Fields . . . . . . . . . . . . . . 111
Appendix A.5. RTP Header Fields . . . . . . . . . . . . . . . . 112
Appendix A.6. ESP Header Fields . . . . . . . . . . . . . . . . 114
Appendix A.7. IPv6 Extension Header Fields . . . . . . . . . . . 114
Appendix A.8. GRE Header Fields . . . . . . . . . . . . . . . . 115
Appendix A.9. MINE Header Fields . . . . . . . . . . . . . . . . 116
Appendix A.10. AH Header Fields . . . . . . . . . . . . . . . . . 117
Appendix B. Compressor Implementation Guidelines . . . . . . . 117
Appendix B.1. Reference Management . . . . . . . . . . . . . . . 118
Appendix B.2. Window-based LSB Encoding (W-LSB) . . . . . . . . 118
Appendix B.3. W-LSB Encoding and Timer-based Compression . . . . 118
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 119
Intellectual Property and Copyright Statements . . . . . . . . . 120
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1. Introduction
The ROHC WG has developed a header compression framework on top of
which various profiles can be defined for different protocol sets or
compression requirements. The ROHC framework was first documented in
[RFC3095], together with profiles for compression of RTP/UDP/IP
(Real-Time Transport Protocol, User Datagram Protocol, Internet
Protocol), UDP/IP, IP and ESP/IP (Encapsulating Security Payload)
headers. Additional profiles for compression of IP headers [RFC3843]
and UDP-Lite (User Datagram Protocol Lite) headers [RFC4019] were
later specified to complete the initial set of ROHC profiles.
This document defines an updated version for each of the above
mentioned profiles, and its definition is based on the specification
of the ROHC framework as found in [RFC4995].
Specifically, this document defines header compression schemes for:
o RTP/UDP/IP : profile 0x0101
o UDP/IP : profile 0x0102
o ESP/IP : profile 0x0103
o IP : profile 0x0104
o RTP/UDP-Lite/IP : profile 0x0107
o UDP-Lite/IP : profile 0x0108
ROHCv2 compresses the following type of extension headers:
o AH [RFC4302]
o GRE [RFC2784][RFC2890]
o MINE [RFC2004]
o NULL-encrypted ESP [RFC4303]
o IPv6 Destination Options header[RFC2460]
o IPv6 Hop-by-hop Options header[RFC2460]
o IPv6 Routing header [RFC2460].
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
This document is consistent with the terminology found in the ROHC
framework [RFC4995] and in the formal notation for ROHC [RFC4997].
In addition, this document uses or defines the following terms:
Acknowledgment Number
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The Acknowledgment Number identifies what packet is being
acknowledged in the RoHCv2 feedback element. The value of this
field normally corresponds to the Master Sequence Number (MSN) of
the header that was last successfully decompressed, for the
compression context (CID) for which the feedback information
applies.
Chaining of Items
A chain of items groups fields based on similar characteristics.
ROHCv2 defines chain items for static, dynamic and irregular
fields. Chaining is achieved by appending to the chain an item
for e.g. each header in their order of appearance in the
uncompressed packet. Chaining is useful to construct compressed
headers from an arbitrary number of any of the protocol headers
for which a ROHCv2 profile defines a compressed format.
CRC-3 Control Validation
The CRC-3 control validation refers to the validation of the
control fields when receiving a CO header that contains a 3-bit
CRC calculated over the control fields that it carries and over
specific control fields in the context. In the formal definition
of the header formats, the 3-bit CRC is labelled "control_crc3"
and uses the "control_crc3_encoding" (See also Section 6.6.11).
Delta
The delta refers to the difference in the absolute value of a
field between two consecutive packets being processed by the same
compression endpoint.
Reordering Depth
The number of packets by which a packet is received late within
its sequence due to reordering between the compressor and the
decompressor, i.e. reordering between packets associated with the
same context (CID). See definition of sequentially late packet
below.
ROHCv2 Packet Types
ROHCv2 profiles use two different packet types: the Initialization
and Refresh (IR) packet type, and the Compressed (CO) packet type.
Sequentially Early Packet
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A packet that reaches the decompressor before one or several
packets that were delayed over the channel, whereas all of the
said packets belong to the same header-compressed flow and are
associated to the same compression context (CID). At the time of
the arrival of a sequentially early packet, the packet(s) delayed
on the link cannot be differentiated from lost packet(s).
Sequentially Late Packet
A packet is late within its sequence if it reaches the
decompressor after one or several other packets belonging to the
same CID have been received, although the sequentially late packet
was sent from the compressor before the other packet(s). How the
decompressor detects a sequentially late packet is outside the
scope of this specification, but it can for example use the MSN to
this purpose.
Timestamp Stride (ts_stride)
The timestamp stride (ts_stride) is the expected increase in the
timestamp value between two RTP packets with consecutive sequence
numbers. For example, for a media encoding with a sample rate of
8 kHz producing one frame every 20ms, the RTP timestamp will
typically increase by n * 160 (= 8000 * 0.02), for some integer n.
Time Stride (time_stride)
The time stride (time_stride) is the time interval equivalent to
one ts_stride, e.g., 20 ms in the example for the RTP timestamp
increment above.
3. Acronyms
This section lists most acronyms used for reference, in addition to
those defined in [RFC4995].
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AH Authentication Header.
ESP Encapsulating Security Payload.
GRE Generic Routing Encapsulation.
FC Full Context state (decompressor).
IP Internet Protocol.
LSB Least Significant Bits.
MINE Minimal Encapsulation in IP.
MSB Most Significant Bits.
MSN Master Sequence Number.
NC No Context state (decompressor).
OA Optimistic Approach.
RC Repair Context state (decompressor).
ROHC Header compression framework (RFC4995).
ROHCv2 Set of header compression profiles defined in this document.
RTP Real-time Transport Protocol.
SSRC Synchronization source. Field in RTP header.
CSRC Contributing source. Optional list of CSRCs in RTP header.
TC Traffic Class. Octet in IPv6 header. See also TOS.
TOS Type Of Service. Octet in IPv4 header. See also TC.
TS RTP Timestamp.
UDP User Datagram Protocol.
UDP-Lite User Datagram Protocol Lite.
4. Background (Informative)
This section provides background information on the compression
profiles defined in this document. The fundamentals of general
header compression and of the ROHC framework may be found in section
3 and 4 of [RFC4995], respectively. The fundamentals of the formal
notation for ROHC are defined in [RFC4997]. [RFC4224] describes the
impacts of out-of-order delivery on profiles based on [RFC3095].
4.1. Classification of header fields
Section 3.1 of [RFC4995] explains that header compression is possible
due to the fact that there is much redundancy between field values
within the headers of a packet, but especially between the headers of
consecutive packets.
Appendix A lists and classifies in detail all the header fields
relevant to this document. The appendix concludes with
recommendations on how the various fields should be handled by header
compression algorithms.
The main conclusion is that most of the header fields can easily be
compressed away since they never or seldom change. A small number of
fields however need more sophisticated mechanisms.
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These fields are:
- IPv4 Identification (16 bits) - IP-ID
- ESP Sequence Number (32 bits) - ESP SN
- UDP Checksum (16 bits) - Checksum
- UDP-Lite Checksum (16 bits) - Checksum
- UDP-Lite Checksum Coverage (16 bits) - CCov
- RTP Marker ( 1 bit ) - M-bit
- RTP Sequence Number (16 bits) - RTP SN
- RTP Timestamp (32 bits) - TS
In particular, for RTP, the analysis in Appendix A reveals that the
values of the RTP Timestamp (TS) field usually have a strong
correlation to the RTP Sequence Number (SN), which increments by one
for each packet emitted by an RTP source. The RTP M-bit is expected
to have the same value most of the time, but it needs to be
communicated explicitly on occasion.
For UDP, the Checksum field cannot be inferred or recalculated at the
receiving end without violating its end-to-end properties, and is
thus sent as-is when enabled (mandatory with IPv6). The same applies
to the UDP-Lite Checksum (mandatory with both IPv4 and IPv6), while
the UDP-Lite Checksum Coverage may in some cases be compressible.
For IPv4, a similar correlation as the one of the RTP TS to the RTP
SN is often observed between the Identifier field (IP-ID) and the
master sequence number used for compression (e.g. the RTP SN when
compressing RTP headers).
4.2. Improvements of ROHCv2 over RFC3095 profiles
The ROHCv2 profiles can achieve compression efficiency and robustness
that are both at least equivalent to RFC3095 profiles, when used
under the same operating conditions. In particular, the size and bit
layout of the smallest compressed header (i.e. PT-0 format U/O-0 in
RFC3095, and pt_0_crc3 in ROHCv2) are identical.
There are a number of differences and improvements between profiles
defined in this document and their earlier version defined in RFC3095
[RFC3095]. This section provides an overview of some of the most
significant improvements:
Tolerance to reordering
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Profiles defined in RFC3095 require that the channel between
compressor and decompressor provide in-order delivery between
compression endpoints. ROHCv2 profiles, however, can handle
robustly and efficiently a limited amount of reordering before and
after the compression point as part of the compression algorithm
itself.
Operational logic
Profiles in RFC3095 define multiple operational modes, each with
different updating logic and compressed header formats. ROHCv2
profiles operate in unidirectional operation until feedback is
first received for a context (CID), at which point bidirectional
is used; the formats are independent of what operational logic is
used.
IP extension header
Profiles in RFC3095 compressed IP Extension headers using list
compression. ROHCv2 profiles instead treat extension headers in
the same manner as other protocol headers, i.e. using the chaining
mechanism; it thus assumes that extension header are not added or
removed during the lifetime of a context (CID), otherwise
compression has to be restarted for this flow.
IP encapsulation
Profiles in RFC3095 can compress at most two levels of IP headers.
ROHCv2 profiles can compress an arbitrary number of IP headers.
List compression
ROHCv2 profiles does not support reference-based list compression.
Robustness and repairs
ROHCv2 profiles do not define a format for the IR-DYN packet;
instead, each profile defines a compressed header that can be used
to perform a more robust context repair using a 7-bit CRC
verification. This also implies that only the IR header can
change the association between a CID and the profile it uses.
Feedback
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ROHCv2 profiles define a CRC in the format of the FEEDBACK-2, and
different feedback options are available.
4.3. Operational Characteristics of ROHCv2 Profiles
Robust header compression can be used over many type of link
technologies. Section 4.4 of [RFC4995] lists the operational
characteristics of the ROHC channel. The ROHCv2 profiles address a
wide range of applications, and this section summarizes some of the
operational characteristics that are specific to these profiles.
Packet length
ROHCv2 profiles assume that the lower layer indicates the length
of a compressed packet. ROHCv2 compressed headers do not contain
length information for the payload.
Out-of-order delivery between compression endpoints
The definition of the ROHCv2 profiles places no strict requirement
on the delivery sequence between the compression endpoints, i.e.
packets may be received in a different order than the compressor
sent them and still have a fair probability to be successfully
decompressed.
However, frequent out-of-order delivery and/or significant
reordering depth will negatively impact the compression
efficiency. More specifically, if the compressor can operate
using a proper estimate of the reordering characteristics of the
path between the compression endpoints, larger headers can be sent
more often to increase the robustness against decompression
failures due to out-of-order delivery. Otherwise, the compression
efficiency will be impaired from an increase in the frequency of
decompression failures and recovery attempts.
5. Overview of the ROHCv2 Profiles (Informative)
This section provides an overview of concepts that are important and
useful to the ROHCv2 profiles. These concepts may be used as
guidelines for implementations but they are not part of the normative
definition of the profiles, as these concepts relates to the
compression efficiency of the protocol without impacting the
interoperability characteristics of an implementation.
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5.1. Compressor Concepts
Header compression can be conceptually characterized as the
interaction of a compressor with a decompressor state machine, one
per context. The responsibility of the compressor is to convey the
information needed to successfully decompress a packet, based on a
certain confidence regarding the state of the decompressor context.
This confidence is obtained from the frequency and the type of
information the compressor sends when updating the decompressor
context, from the optimistic approach (Section 5.1.1) and optionally
from feedback messages received from the decompressor.
5.1.1. Optimistic Approach
A compressor always uses the optimistic approach when it performs
context updates. The compressor normally repeats the same type of
update until it is fairly confident that the decompressor has
successfully received the information. If the decompressor
successfully receives any of the headers containing this update,
state will be available for the decompressor to process smaller
compressed headers.
If field X in the uncompressed header changes value, the compressor
uses a packet type that contains an encoding of field X until it has
gained confidence that the decompressor has received at least one
packet containing the new value for X. The compressor normally
selects a compressed format with the smallest header that can convey
the changes needed to achieve confidence.
The number of repetitions that is needed to obtain this confidence is
normally related to the packet loss and out-of-order delivery
characteristics of the link where header compression is used; it is
thus not defined in this document and is left open to
implementations.
5.1.2. Tradeoff between robustness to losses and to reordering
The ability of a header compression algorithm to handle sequentially
late packets is mainly limited by two factors: the interpretation
interval offset of the sliding window used for LSB encoded fields
[RFC4997], and the optimistic approach (See Section 5.1.1) for seldom
changing fields.
LSB encoded fields:
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The interpretation interval offset specifies an upper limit for
the maximum reordering depth, by which is it possible for the
decompressor to recover the original value of a dynamically
changing (i.e. sequentially incrementing) field that is encoded
using W-LSB. Its value is bound to the number of LSB compressed
bits in the compressed header format, and grows with the number of
bits transmitted. However, the offset and the LSB encoding only
provide robustness for the field that it compresses, and
(implicitly) for other sequentially changing fields that are
derived from that field.
This is shown in the figure below:
<--- interpretation interval (size is 2^k) ---->
|------------------+---------------------------|
v_ref-p v_ref v_ref + (2^k-1) - p
Lower Upper
Bound Bound
<--- reordering --> <--------- losses --------->
where p is the maximum negative delta, corresponding to the
maximum reordering depth for which the lsb encoding can recover
the original value of the field;
where (2^k-1) - p is the maximum positive delta, corresponding
to the maximum number of consecutive losses for which the lsb
encoding can recover the original value of the field
where v_ref is the reference value, as defined in the lsb
encoding method in [RFC4997].
There is thus a tradeoff between the robustness against reordering
and the robustness against packet losses, with respect to the
number of MSN bits needed and the distribution of the
interpretation interval between negative and positive deltas in
the MSN.
Seldom changing fields
The optimistic approach (Section 5.1.1) provides the upper limit
for the maximum reordering depth for seldom changing fields.
There is thus a tradeoff between compression efficiency and
robustness. When only information on the MSN needs to be conveyed to
the decompressor, the tradeoff relates to the number of compressed
MSN bits in the compressed header format. Otherwise, the tradeoff
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relates to the implementation of the optimistic approach.
In particular, compressor implementations should adjust their
optimistic approach strategy to match both packet loss and reordering
characteristics. For example, the number of repetitions for each
update of a non-LSB encoded field can be increased. The compressor
can ensure that each update is repeated until it is reasonably
confident that at least one packet containing the change has reached
the decompressor before the first packet sent after this sequence.
5.1.3. Interactions with the Decompressor Context
The compressor normally starts compression with the initial
assumption that the decompressor has no useful information to process
the new flow, and sends Initialization and Refresh (IR) packets.
Initially, when sending the first IR packet for a compressed flow,
the compressor does not expect to receive feedback for that flow,
until such feedback is first received. At this point, the compressor
may then assume that the decompressor will continue to send feedback
in order to repair its context when necessary. The former is
referred to as unidirectional operation, while the latter is called
bidirectional operation.
The compressor can then adjust the compression level (i.e. what
header format it selects) based on its confidence that the
decompressor has the necessary information to successfully process
the compressed headers that it selects. In other words, the
responsibility of the compressor is to ensure that the decompressor
operates with state information that is sufficient to allow
decompression of the most efficient compressed header(s), and to
allow the decompressor to successfully recover that state information
as soon as possible otherwise.
The compressor thus has the entire responsibility to ensure that the
decompressor has the proper information to decompress the type of
compressed header that it sends. In other words, the choice of
compressed header depends on the following factors:
o the outcome of the encoding method applied to each field;
o the optimistic approach, with respect to the characteristics of
the channel;
o the type of operation (unidirectional or bidirectional), and if in
birectional operation, feedback received from the decompressor
(ACKs, NACKs, STATIC-NACK, and options).
Encoding methods normally use previous value(s) from a history of
packets whose headers it has previously compressed. The optimistic
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approach is meant to ensure that at least one compressed header
containing the information to update the state for a field is
received. Finally, feedback indicates what actions the decompressor
has taken with respect to its assumptions regarding the validity of
its context (Section 5.2.2); it indicates what type of compressed
header the decompressor can or cannot decompress.
The decompressor has the means to detect decompression failures for
any type of compressed (CO) header, using the CRC verification.
Depending on the frequency and/or on the type of the failure, it
might send a negative acknowledgement (NACK) or an explicit request
for a complete context update (STATIC-NACK). However, the
decompressor does not have the means to identify the cause of the
failure, and in particular decompression of what field(s) is
responsible for the failure. The compressor is thus always
responsible to determine what is the most suitable response to a
negative acknowledgement, using the confidence it has in the state of
the decompressor context, when selecting the type of compressed
header it will use when compressing a header.
5.2. Decompressor Concepts
The decompressor normally uses the last received and successfully
validated (IR packets) or verified (CO packets) header as the
reference for future decompression. If the received packet is older
than the current reference packet based on the MSN in the compressed
header, the decompressor may refrain from using this packet as the
new reference packet, even if the correctness of its header was
successfully verified.
The decompressor is responsible to always verify the outcome of the
decompression attempt, to update its context when successful and
finally to request context repairs by making coherent usage of
feedback, once it has started using feedback.
Specifically, the outcome of every decompression attempt is verified
using the CRC present in the compressed header; the decompressor
updates the context information when this outcome is successfully
verified; finally if the decompressor uses feedback once for a
compressed flow then it will continue to do so for as long as the
corresponding context is associated with the same profile.
5.2.1. Decompressor State Machine
The decompressor operation may be represented as a state machine
defining three states: No Context (NC), Repair Context (RC) and Full
Context (FC).
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The decompressor starts without a valid context, the NC state. Upon
receiving an IR packet, the decompressor validates the integrity of
its header using the CRC-8 validation. If the IR header is
successfully validated, the decompressor updates the context and uses
this header as the reference header, and moves to the FC state. The
decompressor state machine normally does not leave the FC state once
it has entered this state; only repeated decompression failures will
force the decompressor to transit downwards to a lower state. When
context damage is detected, the decompressor moves to the repair
context (RC) state, where it stays until it successfully verifies a
decompression attempt for a compressed header with a 7-bit CRC or for
an IR header. When static context damage is detected, the
decompressor moves back to the NC state.
Below is the state machine for the decompressor. Details of the
transitions between states and decompression logic are given in the
sub-sections following the figure.
CRC-8(IR) Validation
+----->----->----->----->----->----->----->----->----->----->----+
| CRC-8(IR) |
| !CRC-8(IR) or CRC-7(CO) or or CRC-7(CO) |
| PT not allowed CRC-8(IR) or CRC-3(CO) |
| +--->---+ +--->----->----->----->---+ +--->---->---+ |
| | | | | | | |
| | v | v | v v
+-----------------+ +----------------------+ +--------------------+
| No Context (NC) | | Repair Context (RC) | | Full Context (FC) |
+-----------------+ +----------------------+ +--------------------+
^ ^ Static Context | ^ !CRC-7(CO) or | ^ Context Damage | |
| | Damage Detected | | PT not allowed | | Detected | |
| +--<-----<-----<--+ +----<------<----+ +--<-----<-----<--+ |
| |
| Static Context Damage Detected |
+--<-----<-----<-----<-----<-----<-----<-----<-----<---------+
where:
CRC-8(IR): successful CRC-8 validation for the IR header.
!CRC-8(IR): Unsuccessful CRC-8 validation for the IR header.
CRC-7(CO) and/or CRC-3(CO): successful CRC verification for the
decompression of a CO header, based on the number of CRC bits
carried in the CO header.
!CRC-7(CO): failure to CRC verify the decompression of a CO header
carrying a 7-bit CRC.
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PT not allowed: the decompressor has received a packet type (PT)
for which the decompressor's current context does not provide
enough valid state information for that packet to be decompressed.
Static Context Damaged Detected: see definition in Section 5.2.2.
Context Damage Detected: see definition in Section 5.2.2.
5.2.1.1. No Context (NC) State
Initially, while working in the No Context (NC) state, the
decompressor has not yet successfully validated an IR header.
Attempting decompression:
In the NC state, only packets carrying sufficient information on
the static fields (i.e. IR packets) can be decompressed.
Upward transition:
The decompressor can move to the Full Context (FC) state when the
CRC validation of an 8-bit CRC in an IR header is successful.
Feedback logic:
In the No Context state, the decompressor should send a STATIC-
NACK if a packet of a type other than IR is received, or if an IR
header has failed the CRC-8 validation, subject to the feedback
rate limitation as described in Section 5.2.3.
5.2.1.2. Repair Context (RC) State
In the Repair Context (RC) state, the decompressor has successfully
decompressed packets for this context, but does not have confidence
that the entire context is valid.
Attempting decompression:
In the RC state, only headers covered by an 8-bit CRC (i.e. IR)
or CO headers carrying a 7-bit CRC can be decompressed.
Upward transition:
The decompressor can move to the Full Context (FC) state when the
CRC verification succeeds for a CO header carrying a 7-bit CRC or
validation of an 8-bit CRC in an IR header.
Downward transition:
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The decompressor moves back to the NC state if it assumes static
context damage.
Feedback logic:
In the RC state, the decompressor should send a STATIC-NACK when
CRC-8 validation of an IR fails, or when a CO header carrying a
7-bit CRC fails and static context damage is assumed, subject to
the feedback rate limitation as described in Section 5.2.3. If
any other packet type is received, the decompressor should treat
it as a CRC verification failure when deciding if a NACK is to be
sent.
5.2.1.3. Full Context (FC) State
In the Full Context (FC) state, the decompressor assumes that its
entire context is valid.
Attempting decompression:
In the FC state, decompression can be attempted regardless of the
type of packet received.
Downward transition:
The decompressor moves back to the RC state if it assumes context
damage. If the decompressor assumes static context damage, it
moves directly to the NC state.
Feedback logic:
In the FC state, the decompressor should send a NACK when CRC-8
validation or CRC verification of any header type fails and if
context damage is assumed, or STATIC-NACK if static context damage
is assumed, subject to the feedback rate limitation as described
in Section 5.2.3.
5.2.2. Decompressor Context Management
All header formats carry a CRC and are context updating. A packet
for which the CRC succeeds updates the reference values of all header
fields, either explicitly (from the information about a field carried
within the compressed header) or implicitly (fields that are inferred
from other fields).
The decompressor may assume that some or the entire context is
invalid, when it fails to validate or to verify one or more headers
using the CRC. Because the decompressor cannot know the exact
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reason(s) for a CRC failure or what field caused it, the validity of
the context hence does not refer to what specific part(s) of the
context is deemed valid or not.
Validity of the context rather relates to the detection of a problem
with the context. The decompressor first assume that the type of
information that most likely caused the failure(s) is the state that
normally changes for each packet, i.e. context damage of the dynamic
part of the context. Upon repeated decompression failures and
unsuccessful repairs, the decompressor then assumes that the entire
context, including the static part, needs to be repaired, i.e. static
context damage. Failure to validate the 3-bit CRC that protects
control fields should be treated as a decompression failure when the
decompressor asserts the validity of its context.
Context Damage Detection
The assumption of context damage means that the decompressor will
not attempt decompression of a CO header that carries only a 3-bit
CRC, and will only attempt decompression of IR headers, or CO
headers protected by a CRC-7.
Static Context Damage Detection
The assumption of static context damage means that the
decompressor refrains from attempting decompression of any type of
header other than the IR header.
How these assumptions are made, i.e. how context damage is detected,
is open to implementations. It can be based on the residual error
rate, where a low error rate makes the decompressor assume damage
more often than on a high rate link.
The decompressor implements these assumptions by selecting the type
of compressed header for which it will attempt decompression. In
other words, validity of the context refers to the ability of a
decompressor to attempt or not decompression of specific packet
types.
When ROHCv2 profiles are used over a channel that cannot guarantee
in-order delivery, the decompressor may refrain from updating its
context with the content of a sequentially late packet that is
successfully decompressed. This is to avoid updating the context
with information that is older than what the decompressor already has
in its context.
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5.2.3. Feedback logic
ROHCv2 profiles may be used in environments with or without feedback
capabilities from decompressor to compressor. ROHCv2 however assumes
that if a ROHC feedback channel is available and if this channel is
used at least once by the decompressor for a specific context, this
channel will be used during the entire compression operation for that
context (i.e. bidirectional operation).
The ROHC framework defines 3 types of feedback messages: ACKs, NACKs
and STATIC-NACKs. The semantics of each message if defined in
section 5.2.3.1. of [RFC4995]. What feedback to send is coupled to
the context management of the decompressor, i.e. to the
implementation of the context damage detection algorithms as
described in Section 5.2.2.
The decompressor should send a NACK when it assumes context damage,
and it should send a STATIC-NACK when it assumes static context
damage. The decompressor is not strictly expected to send ACK
feedback upon successful decompression, other than for the purpose of
improving compression efficiency.
When ROHCv2 profiles are used over a channel that cannot guarantee
in-order delivery, the decompressor may refrain to send ACK feedback
for a sequentially late packet that is successfully decompressed.
The decompressor should limit the rate at which it sends feedback,
for both ACKs and STATIC-NACK/NACKs, and should avoid sending
unnecessary duplicates of the same type of feedback message that may
be associated to the same event.
6. ROHCv2 Profiles (Normative)
6.1. Channel Parameters, Segmentation and Reordering
The compressor MUST NOT use ROHC segmentation (see [RFC4995] section
5.2.5), i.e. MRRU MUST be set to 0), if the configuration of the
ROHC channel contains at least one ROHCv2 profile in the list of
supported profiles (i.e. the PROFILES parameter) and if the channel
cannot guarantee in-order delivery of packets between compression
endpoints.
6.2. Profile Operation, per-context
ROHCv2 profiles operate differently, per context, depending on how
the decompressor makes use of the feedback channel, if any. Once the
decompressor uses the feedback channel for a context, it establishes
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the feedback channel for that CID.
The compressor always start assuming that the decompressor will not
send feedback when it initializes a new context (see also the
definition of a new context insection 5.1.1. of [RFC4995]), i.e.
there is no established feedback channel for the new context. There
will always be a possibility of decompression failure with the
optimistic approach, because the decompressor may not have received
sufficient information for correct decompression. Therefore, until
the decompressor has established a feedback channel, the compressor
SHOULD periodically send IR packets. The periodicity can be based on
timeouts, on the number of compressed packets sent for the flow, or
any other strategy the implementer chooses.
The reception of either positive feedback (ACKs) or negative feedback
(NACKs or STATIC-NACKs) establishes the feedback channel from the
decompressor for the context (CID) for which the feedback was
received. Once there is an established feedback channel for a
specific context, the compressor can make use of this feedback to
estimate the current state of the decompressor. This helps
increasing the compression efficiency by providing the information
needed for the compressor to achieve the necessary confidence level.
When the feedback channel is established, it becomes superfluous for
the compressor to send periodic refreshes, and instead it can rely
entirely on the optimistic approach and feedback from the
decompressor.
The decompressor MAY send positive feedback (ACKs) to initially
establish the feedback channel for a particular flow. Either
positive feedback (ACKs) or negative feedback (NACKs) establishes
this channel. The decompressor is REQUIRED to continue sending
feedback once it has established a feedback channel for a CID, for
the lifetime of the context, i.e. until the CID is associated with a
different profile from the reception of an IR packet, to send error
recovery requests and (optionally) acknowledgments of significant
context updates.
Compression without an established feedback channel will be less
efficient, because of the periodic refreshes and from the lack of
feedback for initiation of error recovery; there will also be a
slightly higher probability of loss propagation compared to the case
where the decompressor uses feedback.
6.3. Control Fields
ROHCv2 defines a number of control fields that are used by the
decompressor in its interpretation of the packet formats received
from the compressor. The control fields listed in the following
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subsections are all defined in Section 6.8.2.4 using ROHC-FN
[RFC4995].
6.3.1. Master Sequence Number (MSN)
The Master Sequence Number (MSN) field is either taken from a field
that already exists in each of the headers of the protocol that the
profile compresses (e.g. RTP SN), or alternatively it is created at
the compressor. There is one MSN space per context (CID).
The MSN field has the following two functions:
o Differentiating between reference headers when receiving feedback
data.
o Inferring the value of incrementing fields (e.g. IPv4
Identifier).
The MSN field is present in every ROHCv2 header sent by the
compressor. The MSN is sent in full in IR packets, while it can be
sent LSB encoded within CO header formats. The decompressor always
includes LSBs of the MSN in the Acknowledgment Number field in
feedback (see Section 6.9). The compressor can later use this field
to infer what packet the decompressor is acknowledging.
For profiles for which the MSN is created by the compressor, the
following applies:
o The compressor should only initialize a new MSN for the initial IR
sent for a CID that corresponds to a context that is not already
associated with this profile;
o When the MSN is initialized, it is initialized to a random value;
o The value of the MSN is incremented by one for each packet that
the compressor sends for a specific CID.
6.3.2. Reordering Ratio
The control field reorder_ratio specifies how much reordering is
handled by the LSB encoding of the MSN. This is useful when header
compression is performed over links with varying reordering
characteristics. The reorder_ratio control field is a means for the
compressor to adjust the robustness characteristics of the LSB
encoding method with respect to reordering and consecutive losses, as
described in Section 5.1.2.
6.3.3. IP-ID behavior
The IP-ID field of the IPv4 header can have different change
patterns: sequential in network byte order, sequential byte-swapped,
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random or constant (a constant value of zero, although not conformant
with [RFC0791], has been observed in practice). There is one IP-ID
behavior control field per IP header. The control field for the
IP-ID behavior of the innermost IP header determines which set of
header formats will be used. The IP-ID behavior control field is
also used to determine the contents of the irregular chain item, for
each IP header.
ROHCv2 profiles can assign a sequential behavior (network byte order
or byte-swapped) only to the IP-ID of innermost IP header, when
compressing more than one level of IP headers. This is because only
the IP-ID of the innermost IP header is likely to have a sufficiently
close correlation with the MSN to compress it as a sequentially
changing field. Therefore, a compressor MUST assign either the
constant zero IP-ID or the random IP-ID behavior to tunneling
headers.
6.3.4. UDP-Lite Coverage Behavior
The control field coverage_behavior specifies how the checksum
coverage field of the UDP-Lite header is compressed with RoHCv2. It
can indicate one of he following encoding methods: irregular, static
or inferred compression.
6.3.5. Timestamp Stride
The ts_stride control field is used in scaled RTP timestamp encoding
(see Section 6.6.8). It defines the expected increase in the RTP
timestamp between consecutive RTP sequence numbers.
6.3.6. Time Stride
The time_stride control field is used in timer-based compression
encoding (see Section 6.6.9). When timer-based compression is used,
time_stride should be set to the expected difference in arrival time
between consecutive RTP packets.
6.3.7. CRC-3 for Control Fields
ROHCv2 profiles define a CRC-3 calculated over a number of control
fields. This 3-bit CRC protecting the control fields is present in
the header format for the co_common and co_repair header types.
Failure to validate the control fields using this CRC should be
considered as a decompression failure by the decompressor, in the
algorithm that assesses the validity of the context. However, if the
decompression attempt can be verified using either the CRC-3 or the
CRC-7 calculated over the uncompressed header, the decompressor may
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still forward the decompressed header to upper layers. This is
because the protected control fields are not always used for
decompression of the specific co_common or the co_repair header that
updates their respective value.
The CRC polynomial and coverage of this CRC-3 is defined in
Section 6.6.11.
6.4. Reconstruction and Verification
Validation of the IR header (8-bit CRC)
The decompressor MUST always validate the integrity of the IR
header using the 8-bit CRC carried within the IR header. When the
header is validated, the decompressor updates the context with the
information in the IR header. Otherwise, if the IR cannot be
validated, the context MUST NOT be updated and the IR header MUST
NOT be delivered to upper layers.
Verification of CO headers (3-bit CRC or 7-bit CRC)
The CRC carried within compressed headers MUST be used to verify
decompression of CO headers. When the decompression is verified
and successful, the decompressor updates the context with the
information received in the CO header; otherwise if the
reconstructed header fails the CRC verification, these updates
MUST NOT be performed.
A packet for which the decompression attempt cannot be verified
using the CRC MUST NOT be delivered to upper layers.
Decompressor implementations may attempt corrective or repair
measures on CO headers prior to performing the above actions, and
the result of any decompression attempt MUST be verified using the
CRC.
6.5. Compressed Header Chains
Some packet types use one or more chains containing sub-header
information. The function of a chain is to group fields based on
similar characteristics, such as static, dynamic or irregular fields.
Chaining is done by appending an item for each header to the chain in
their order of appearance in the uncompressed packet, starting from
the fields in the outermost header.
Static chain:
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The static chain consists of one item for each header of the chain
of protocol headers to be compressed, starting from the outermost
IP header. In the formal description of the packet formats, this
static chain item for each header type is labelled
<protocol_name>_static. The static chain is only used in the IR
header format.
Dynamic chain:
The dynamic chain consists of one item for each header of the
chain of protocol headers to be compressed, starting from the
outermost IP header. In the formal description of the packet
formats, the dynamic chain item for each header type is labelled
<protocol_name>_dynamic. The dynamic chain is only used in the IR
header format.
Irregular chain:
The structure of the irregular chain is analogous to the structure
of the static chain. For each compressed packet, the irregular
chain is appended at the specified location in the general format
of the compressed packets as defined in Section 6.8. The
irregular chain is used in all CO packets.
The format of the irregular chain for the innermost IP header
differs from the format used for the outer IP headers, because
this header is part of the compressed base header. In the
definition of the packet formats using the formal notation, the
argument "is_innermost" passed to the corresponding encoding
method (ipv4 or ipv6) determines what irregular chain items to
use. The format of the irregular chain item for the outer IP
headers is also determined using one flag for TTL/Hop Limit and
one for TOS/TC. These flags are defined in the format of some of
the compressed base headers.
ROHCv2 profiles compresses extension headers as other headers, and
thus extension headers have a static chain, a dynamic chain and an
irregular chain.
ROHCv2 profiles define chains for all headers that can be compressed,
i.e. RTP [RFC3550], UDP [RFC0768], UDP Lite [RFC3828], IPv4
[RFC0791], IPv6 [RFC2460], AH [RFC4302], GRE [RFC2784][RFC2890], MINE
[RFC2004], NULL-encrypted ESP [RFC4303], IPv6 Destination Options
header[RFC2460], IPv6 Hop-by-hop Options header[RFC2460] and IPv6
Routing header [RFC2460].
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6.6. Packet Formats and Encoding Methods
The packet formats are defined using the ROHC formal notation. Some
of the encoding methods used in the packet formats are defined in
[RFC4997], while other methods are defined in this section.
6.6.1. baseheader_extension_headers
The baseheader_extension_headers encoding method skips over all
fields of the extension headers of the innermost IP header, without
encoding any of the them. Fields in these extension headers are
instead encoded in the irregular chain.
This encoding is used in CO headers (see Section 6.8.2). The
innermost IP header is combined with other header(s) (i.e. UDP, UDP
Lite, RTP) to create the compressed base header. In this case, there
may be a number of extension headers between the IP headers and the
other headers.
The base header defines a representation of the extension headers, to
comply with the syntax of the formal notation; this encoding method
provides this representation.
6.6.2. baseheader_outer_headers
The baseheader_outer_headers encoding method skips over all the
fields of the extension header(s) that do not belong to the innermost
IP header, without encoding any of them. Changing fields in outer
headers are instead handled by the irregular chain.
This encoding method, similarly to the baseheader_extension_headers
encoding method above, is necessary to keep the definition of the
packet formats syntactically correct. It describes tunneling IP
headers and their respective extension headers (i.e. all headers
located before the innermost IP header) for CO headers (see
Section 6.8.2).
6.6.3. inferred_udp_length
The decompressor infers the value of the UDP length field as being
the size of the UDP payload. The compressor must therefore ensure
that the UDP length field is consistent with the length field(s) of
preceeding subheaders, i.e., there must not be any padding after the
UDP payload that is covered by the IP Length.
This encoding method is also used for the UDP-Lite Checksum Coverage
field, when it behaves in the same manner as the UDP length field
(i.e. when the checksum always covers the entire UDP-Lite payload).
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6.6.4. inferred_ip_v4_header_checksum
This encoding method compresses the header checksum field of the IPv4
header. This checksum is defined in RFC 791 [RFC0791] as follows:
Header Checksum: 16 bits
A checksum on the header only. Since some header fields change
(e.g., time to live), this is recomputed and verified at each
point that the internet header is processed.
The checksum algorithm is:
The checksum field is the 16 bit one's complement of the one's
complement sum of all 16 bit words in the header. For purposes
of computing the checksum, the value of the checksum field is
zero.
As described above, the header checksum protects individual hops from
processing a corrupted header. There is no reason to transmit this
checksum when almost all IP header information is compressed away,
and when decompression is verified by a CRC computed over the
original header for every compressed packet; instead, the checksum
can be recomputed by the decompressor.
The "inferred_ip_v4_header_checksum" encoding method thus compresses
the header checksum field of the IPv4 header down to a size of zero
bits, i.e. no bits are transmitted in compressed headers for this
field. Using this encoding method, the decompressor infers the value
of this field using the computation above.
The compressor MAY use the header checksum to validate the
correctness of the header before compressing it, to avoid processing
a corrupted header.
6.6.5. inferred_mine_header_checksum
This encoding method compresses the minimal encapsulation header
checksum. This checksum is defined in RFC 2004 [RFC2004] as follows:
Header Checksum
The 16-bit one's complement of the one's complement sum of all
16-bit words in the minimal forwarding header. For purposes of
computing the checksum, the value of the checksum field is 0.
The IP header and IP payload (after the minimal forwarding
header) are not included in this checksum computation.
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The "inferred_mine_header_checksum" encoding method compresses the
minimal encapsulation header checksum down to a size of zero bits,
i.e. no bits are transmitted in compressed headers for this field.
Using this encoding method, the decompressor infers the value of this
field using the above computation.
The motivations for inferring this checksum are similar to the ones
explained above in Section 6.6.4.
The compressor MAY use the minimal encapsulation header checksum to
validate the correctness of the header before compressing it, to
avoid processing a corrupted header.
6.6.6. inferred_ip_v4_length
This encoding method compresses the total length field of the IPv4
header. The total length field of the IPv4 header is defined in RFC
791 [RFC0791] as follows:
Total Length: 16 bits
Total Length is the length of the datagram, measured in octets,
including internet header and data. This field allows the
length of a datagram to be up to 65,535 octets.
The "inferred_ip_v4_length" encoding method compresses the IPv4
header checksum down to a size of zero bits, i.e. no bits are
transmitted in compressed headers for this field. Using this
encoding method, the decompressor infers the value of this field by
counting in octets the length of the entire packet after
decompression.
6.6.7. inferred_ip_v6_length
This encoding method compresses the payload length field in the IPv6
header. This length field is defined in RFC 2460 [RFC2460] as
follows:
Payload Length: 16-bit unsigned integer
Length of the IPv6 payload, i.e., the rest of the packet
following this IPv6 header, in octets. (Note that any
extension headers present are considered part of the payload,
i.e., included in the length count.)
The "inferred_ip_v6_length" encoding method compresses the payload
length field of the IPv6 header down to a size of zero bits, i.e. no
bits are transmitted in compressed headers for this field. Using
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this encoding method, the decompressor infers the value of this field
by counting in octets the length of the entire packet after
decompression.
6.6.8. Scaled RTP Timestamp Encoding
The RTP timestamp (TS) usually increases by a multiple of the RTP
Sequence Number's (SN) increase and is therefore a suitable candidate
for scaled encoding. This scaling factor is labeled ts_stride in the
definition of the profile in ROHC-FN Section 6.8. The compressor
sets the scaling factor based on the change in TS with respect to the
change in the RTP SN.
As defined in Section 6.8.2.4, the initial value of the scaling
factor ts_stride is always set to 160. For the compressor to start
using scaled encoding using a value different than this default
value, it must first explicitly transmit the new value of ts_stride
to the decompressor, using one of the packet types that can carry
this information. If the compressor decides to use the default
value, the stride does not need to be transmit in this step.
Once the value of the scaling factor is established, before using the
new scaling factor, the compressor must have enough confidence that
the decompressor has successfully calculated the residue (ts_offset)
of the scaling function for the timestamp. This is done by sending
unscaled timestamp values to allow the decompressor to establish the
residue based on the current ts_stride. The compressor MAY send the
unscaled timestamp in the same packets as the ones establishing the
new ts_stride value.
Once the compressor has gained enough confidence that both the value
of the scaling factor and the value of the residue have been
established in the decompressor, the compressor can start compressing
packets using the new scaling factor.
If the compressor notices that the residue (ts_offset) value changes,
the compressor cannot use scaled timestamp packet formats until it
has re-established the residue as described above.
If the decompressor receives a packet containing scaled timestamp
bits while the ts_stride equals zero, it MUST NOT deliver the packet
to upper layers.
When the value of the timestamp field wraps around, the value of the
residue of the scaling function is likely to change. When this
occurs, the compressor re-establishes the new residue value as
described above.
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The compressor MAY use the scaled timestamp encoding; what value it
will use as the scaling factor is up to the compressor
implementation, but to achive any gains from the scaling, the
ts_stride should be set to the value of the expected incease in
timestamp between consecutive sequence numbers.
When scaled timestamp encoding is used for packet formats that do not
transmit any LSB-encoded timestamp bits at all, the
inferred_scaled_field encoding of Section 6.6.10 is used for encoding
the timestamp.
6.6.9. timer_based_lsb
The timer-based compression encoding method, "timer_based_lsb",
compresses a field whose change pattern approximates a linear
function of the time of day.
This encoding uses the local clock to obtain an approximation of the
value that it encodes. The approximated value is then used as a
reference value together with the num_lsbs_param least-significant
bits received as the encoded value, where num_lsbs_param represents a
number of bits that is sufficient to uniquely represent the encoded
value in the presence of jitter between compression endpoints.
The clock resolution of the compressor or decompressor can be less
than time_stride; in this case, the difference, i.e., actual
resolution - time_stride, is treated as additional jitter in the
calculation of the number of LSBs that needs to be transmitted.
ts_scaled =:= timer_based_lsb(<time_stride_param>,
<num_lsbs_param>, <offset_param>)
The parameters "num_lsbs_param" and "offset_param" are the parameters
to use for the lsb encoding, i.e. the number of least significant
bits and the interpretation interval offset, respectively. The
parameter "time_stride_param" represents the context value of the
control field time_stride.
This encoding method always uses a scaled version of the field it
compresses.
The value of the field is decoded by calculating an approximation of
the uncompressed value, using:
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tsc_ref_advanced = tsc_ref + (a_n - a_ref) / time_stride.
where:
- tsc_ref is a reference value of the scaled representation
of the field.
- a_n is the arrival time associated to the value to decode.
- a_ref is the arrival time associated to the reference header.
- tsc_ref_advanced is an approximation of the uncompressed value
of the field.
The lsb() encoding is then applied using the num_lsbs_param bits
received in the CO header and tsc_ref_advanced as "ref_value" (as per
Section 4.11.5 of [RFC4997]).
Appendix B.3 provides an example on how the compressor can calculate
jitter.
The control field time_stride controls whether or not the
timer_based_lsb method is used in the CO header. The decompressor
SHOULD send the CLOCK_RESOLUTION option if it receives a non-zero
time_stride value and it has not previously informed the compressor
that it supports timer-based compression using the CLOCK_RESOLUTION
option with a non-zero value. Whether the CLOCK_RESOLUTION is set to
a non-zero value or to a zero value is up to the implementation.
The support and usage of timer-based compression is optional for both
the compressor and the decompressor; the compressor is never required
to set the time_stride control field to a non-zero value when it has
received a non-zero value for the CLOCK_RESOLUTION option.
6.6.10. inferred_scaled_field
The "inferred_scaled_field" encoding method is used to encode a field
that is defined as changing in relation to the MSN but for each
increase is scaled by an established scaling factor. This encoding
method is to be used in the case when a packet format contains MSN
bits, but does not contain any bits for the scaled field. In this
case, the new value for the field being scaled is calculated
according to the following formula:
unscaled_value = delta_msn * stride + reference_unscaled_value
Where "delta_msn" is the difference in MSN between the reference
value of the MSN in the context and the value of the MSN decompressed
from this packet, "reference_unscaled_value" is the value of the
field being scaled in the context, and "stride" is the scaling value
for this field.
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For example, when this encoding method is applied to the RTP
timestamp in the RTP profile, the calculation above becomes:
timestamp = delta_msn * ts_stride + reference_timestamp
6.6.11. control_crc3_encoding
The "control_crc3_encoding" method provides a CRC calculated over a
number of control fields. The definition of this encoding method is
the same as for the "crc" encoding method specified in section 4.11.6
of [RFC4997], with the difference that the data that is covered by
the CRC is given by a concatenated list of control fields.
In other words, the definition of the control_crc3_encoding method is
equivalent to the following definition:
control_crc_encoding(data_value, data_length)
{
UNCOMPRESSED {
}
COMPRESSED {
control_crc3 =:=
crc(3, 0x06, 0x07, ctrl_data_value, ctrl_data_length) [ 3 ];
}
}
where the parameter "ctrl_data_value" binds to the concatenated
values of the following control fields, in the order listed below:
o reorder_ratio, 2 bits padded by 6 MSB of zeroes
o ts_stride, 32 bits (applicable only for profiles 0x0101 and
0x0107)
o time_stride, 32 bits (applicable only for profiles 0x0101 and
0x0107)
o msn, 16 bits (not applicable for profiles 0x0101 and 0x0107, since
the RTP Sequence Number is already verified as part of the
uncompressed header)
o coverage_behavior, 2 bits padded by 6 MSB of zeroes, applicable
only to profiles 0x0107 and 0x0108
o ip_id_behavior, one octet for each IP header in the compressible
header chain starting from the outermost header. Each octet
consists of 2 bits padded by 6 MSBs of zeroes
The "ctrl_data_length" binds to the sum of the length of the control
field(s) that are applicable.
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A 3-bit CRC is used to validate the control fields that are updated
by the co_common and co_repair packet types; it cannot verify the
outcome of a decompression attempt. The definition of this CRC comes
from the fact that the decompression of a header that carries and
updates control fields does not necessarily make use of these control
fields, and the update to the control fields is thus not protected by
the CRC-7 validation.
For example, without a verification of the updates to the control
fields, there would be a possibility that a decompression attempt
succeeds for a co_common or for a co_repair packet for which the
decompressor would send a positive feedback, even in the case where
one of the control fields had been corrupted on the link between the
compression endpoints.
6.6.12. inferred_sequential_ip_id
This encoding method is used when a sequential IP-ID behavior is used
(sequential or sequential byte-swapped) and no coded IP-ID bits are
present in the compressed header. When these packet types are used,
the IP-ID offset from the MSN will be constant, and therefore, the
IP-ID will increase by the same amount as the MSN increases by
(similar to the inferred_scaled_field encoding method).
Therefore, the new value for the IP-ID is calculated according to the
following formula:
IP-ID = delta_msn + reference_IP_ID_value
Where "delta_msn" is the difference is MSN between the reference
value of MSN in the context and the value of the MSN decompressed
from this packet, "previous_IP_ID_value" is the value of the IP-ID in
the context.
If the IP-ID behavior is random or zero, this encoding method does
not update any fields.
6.6.13. list_csrc(cc_value)
This encoding method describes how the list of CSRC identifiers can
be compressed using list compression. This list compression operates
by establishing content for the different CSRC identifiers (items)
and list describing the order that they appear.
The argument to this encoding method (cc_value) is the value of the
CC field from the RTP header which the compressor passes to this
encoding method. The decompressor is required to bind the value of
this argument to the number of items in the list, which will allow
the decompressor to corectly reconstruct the CC field.
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6.6.13.1. List Compression
The CSRC identifiers in the uncompressed packet can be represented as
an ordered list, whose order and presence are usually constant
between packets. The generic structure of such a list is as follows:
+--------+--------+--...--+--------+
list: | item 1 | item 2 | | item n |
+--------+--------+--...--+--------+
When performing list compression on a CSRC list, each item is the
uncompressed value of one CSRC identifier.
The basic principles of list-based compression are the following:
1) When a context is being initialized, a complete representation
of the list of CSRC identifiers is transmitted.
Then, once the context has been initialized:
2) When the structure of the list is unchanged, no information
about the list is sent in compressed headers.
3) When the structure of the list changes, a compressed list is
sent in the compressed header, including a representation of its
structure and order. Previously unknown items are sent
uncompressed in the list, while previously known items are only
represented by an index pointing to the context.
6.6.13.2. Table-based Item Compression
The Table-based item compression compresses individual items sent in
compressed lists. The compressor assigns a unique identifier,
"Index", to each item "Item" of a list.
Compressor Logic
The compressor conceptually maintains an Item Table containing all
items, indexed using "Index". The (Index, Item) pair is sent
together in compressed lists until the compressor gains enough
confidence that the decompressor has observed the mapping between
items and their respective index. Confidence is obtained from the
reception of an acknowledgment from the decompressor, or by
sending (Index, Item) pairs using the optimistic approach. Once
confidence is obtained, the index alone is sent in compressed
lists to indicate the presence of the item corresponding to this
index.
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The compressor may reset its item table upon receiving negative
acknowledgement.
The compressor may reassign an existing index to a new item, by
re-establishing the mapping using the procedure described above.
Decompressor Logic
The decompressor conceptually maintains an Item Table that
contains all (Index, Item) pairs received. The Item Table is
updated whenever an (Index, Item) pair is received and
decompression is successfully verified using the CRC. The
decompressor retrieves the item from the table whenever an Index
without an accompanying Item is received.
If an index without an accompanying item is received and the
decompressor does not have any context for this index, the packet
MUST NOT be delivered to upper layers.
6.6.13.3. Encoding of Compressed Lists
Each item present in a compressed list is represented by:
o an index into the table of items, and
o a presence bit indicating if a compressed representation of the
item is present in the list.
o an item (if the presence bit is set)
If the presence bit is not set, the item must already be known by the
decompressor.
A compressed list of items uses the following encoding:
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| Reserved |PS | m |
+---+---+---+---+---+---+---+---+
| XI_1, ..., XI_m | m octets, or m * 4 bits
/ --- --- --- ---/
| : Padding : if PS = 0 and m is odd
+---+---+---+---+---+---+---+---+
| |
/ item_1, ..., item_n / variable
| |
+---+---+---+---+---+---+---+---+
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Reserved: Must be set to zero.
PS: Indicates size of XI fields:
PS = 0 indicates 4-bit XI fields;
PS = 1 indicates 8-bit XI fields.
m: Number of XI item(s) in the compressed list. Also the value of
the cc_value argument.
XI_1, ..., XI_m: m XI items. Each XI represents one item in the
list of item of the uncompressed header, in the same order as they
appear in the uncompressed header.
The format of an XI item is as follows:
+---+---+---+---+
PS = 0: | X | Index |
+---+---+---+---+
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
PS = 1: | X | Reserved | Index |
+---+---+---+---+---+---+---+---+
X: Indicates whether the item present in the list:
X = 1 indicates that the item corresponding to the Index is
sent in the item_1, ..., item_n list;
X = 0 indicates that the item corresponding to the Index is
not sent.
Reserved: Set to zero when sending, ignored when received.
Index: An index into the item table. See Section 6.6.13.4
When 4-bit XI items are used and, the XI items are placed in
octets in the following manner:
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| XI_k | XI_k + 1 |
+---+---+---+---+---+---+---+---+
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Padding: A 4-bit padding field is present when PS = 0 and the
number of XIs is odd. The Padding field is set to zero when
sending and ignored when receiving.
Item 1, ..., item n: Each item corresponds to an XI with X = 1 in
XI 1, ..., XI m. Each entry in the item list is the uncompressed
representation of one CSRC identifier.
6.6.13.4. Item Table Mappings
The item table for list compression is limited to 16 different items,
since the RTP header can only carry at most 15 simultaneous CSRC
identifiers. The effect of having more than 16 items will only cause
a slight overhead to the compressor when items are swapped in/out of
the item table.
6.6.13.5. Compressed Lists in Dynamic Chain
A compressed list that is part of the dynamic chain (i.e. in IR
packets) must have all its list items present, i.e. all X-bits in the
XI list MUST be set. All items previously established in the item
table that are not present in the list decompressed from this packet
MUST also be retained in the decompressor context.
6.7. Encoding Methods With External Parameters
A number of encoding methods in Section 6.8.2.4 have one or more
arguments for which the derivation of the parameter's value is
outside the scope of the ROHC-FN specification of the header formats.
This section lists the encoding methods together with a definition of
each of their parameters.
o esp_null(next_header_value):
next_header_value: Set to the value of the Next Header field
located in the ESP trailer, usually 12 octets from the end of
the packet. Compression of null-encrypted ESP headers should
only be performed when the compressor has prior knowledge of
the exact location of the next header field.
o ipv6(profile, is_innermost, outer_ip_flag)):
profile: Set to the 16-bit profile number of the profile used
to compress this packet.
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is_innermost: This boolean flag is set to 1 when processing the
innermost IP header; otherwise it is set to 0.
outer_ip_flag: This parameter is set to 1 if one or more of a
number of semi-static fields in outer IP headers have changed
compared to their reference values in the context, otherwise it
is set to 0. The value used for this parameter is also used
for the "outer_ip_flag" argument for a number of encoding
methods defined above, when these are processing the irregular
chain. This flag may only be set to 1 for the "co_common"
packet format in the different profiles.
o ipv4(profile, is_innermost, outer_ip_flag)
See definition of arguments for "ipv6" above.
o udp(profile)
profile: Set to the 16-bit profile number of the profile used
to compress this packet.
o rtp(profile, ts_stride_value, time_stride_value)
profile: Set to the 16-bit profile number of the profile used
to compress this packet.
ts_stride_value: The value of this parameter should be set to
the expected increase in the RTP Timestamp between consecutive
RTP sequence numbers and the selected value is implementation-
specific. See also Section 6.6.8.
time_stride_value: The value of this parameter should be set to
the expected inter-arrival time between consecutive packets for
the flow, and the selected value is implementation-specific.
It MUST NOT be set to a non-zero value, unless the compressor
has received a feedback message with the CLOCK_RESOLUTION
option set to a non-zero value. See also Section 6.6.9.
o esp(profile)
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profile: Set to the 16-bit profile number of the profile used
to compress this packet.
o udp_lite(profile)
profile: Set to the 16-bit profile number of the profile used
to compress this packet.
o rtp_baseheader(profile, ts_stride_value, time_stride_value,
outer_ip_flag):
profile: Set to the 16-bit profile number of the profile used
to compress this packet.
ts_stride_value: The value of this parameter should be set to
the expected increase in the RTP Timestamp between consecutive
RTP sequence numbers and the selected value is implementation-
specific. See also Section 6.6.8.
time_stride_value: The value of this parameter should be set to
the expected inter-arrival time between consecutive packets for
the flow, and the selected value is implementation-specific.
It MUST NOT be set to a non-zero value, unless the compressor
has received a feedback message with the CLOCK_RESOLUTION
option set to a non-zero value. See also Section 6.6.9.
outer_ip_flag: This parameter is set to 1 if one or more of a
number of semi-static fields in outer IP headers have changed
compared to their reference values in the context, otherwise it
is set to 0. The value used for this parameter is also used
for the "outer_ip_flag" argument for a number of encoding
methods defined above, when these are processing the irregular
chain. This flag may only be set to 1 either for the
"co_common" packet format in the different profiles.
o udp_baseheader(profile, outer_ip_flag):
profile: Set to the 16-bit profile number of the profile used
to compress this packet.
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outer_ip_flag: See definition of this argument for
"rtp_baseheader" above.
o esp_baseheader(profile, outer_ip_flag):
See definition of arguments for "udp_baseheader" above.
o iponly_baseheader(profile, outer_ip_flag):
See definition of arguments for "udp_baseheader" above.
o udplite_rtp_baseheader(profile, ts_stride_value,
time_stride_value, outer_ip_flag):
See definition of arguments for "rtp_baseheader" above.
o udplite_baseheader(profile, outer_ip_flag):
See definition of arguments for "udp_baseheader" above.
6.8. Packet Formats
ROHCv2 profiles use two different packet types: the Initialization
and Refresh (IR) packet type, and the Compressed packet type (CO).
Each packet type defines a number of packet formats: An IR packet
format, and two sets base header formats are defined for the CO type
with a few additional formats that are common to both sets.
6.8.1. Initialization and Refresh Packet (IR)
The IR packet format uses the structure of the ROHC IR packet as
defined in [RFC4995], section 5.2.2.1.
Packet type: IR
This packet type communicates the static part and the dynamic part
of the context.
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The ROHCv2 IR packet has the following format:
0 1 2 3 4 5 6 7
--- --- --- --- --- --- --- ---
: Add-CID octet : if for small CIDs and (CID != 0)
+---+---+---+---+---+---+---+---+
| 1 1 1 1 1 1 0 1 | IR type octet
+---+---+---+---+---+---+---+---+
: :
/ 0-2 octets of CID / 1-2 octets if for large CIDs
: :
+---+---+---+---+---+---+---+---+
| Profile | 1 octet
+---+---+---+---+---+---+---+---+
| CRC | 1 octet
+---+---+---+---+---+---+---+---+
| |
/ Static chain / variable length
| |
- - - - - - - - - - - - - - - -
| |
/ Dynamic chain / variable length
| |
- - - - - - - - - - - - - - - -
| |
/ Payload / variable length
| |
- - - - - - - - - - - - - - - -
Static chain: See Section 6.5.
Dynamic chain: See Section 6.5.
Payload: The payload of the corresponding original packet, if any.
The payload consists of all data after the last octet of the last
header compressed by the current profile. The presence of a
payload is inferred from the packet length.
6.8.2. Compressed Packet Formats (CO)
6.8.2.1. Design rationale for compressed base headers
The compressed packet formats are defined as two separate sets for
each profile: one set for the packets where the innermost IP header
contains a sequential IP-ID (either network byte order or byte
swapped), and one set for the packets without sequential IP-ID
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(either random, zero, or no IP-ID). There are also a number of
common packet format shared between both sets. When described below,
the packet formats belonging to the sequential set contain "seq" in
their names, while those belonging to the non-sequential set contain
the "rnd" in their names.
The design of the packet formats is derived from the field behavior
analysis found in Appendix A.
All of the compressed base headers transmit LSB-encoded MSN bits and
a CRC.
The following packet formats exist for all profiles defined in this
document, both for the sequential and random packet format sets:
o co_common: The common packet format is designed so that it can be
used for changes to any dynamic field in the context, but can not
always transmit all such fields uncompressed. It is therefore
useful for when some of the more rarely changing fields in the
headers change. Since this packet format may modify the value of
the control fields that determine how the decompressor interprets
different compressed header format, it carries a 7-bit CRC to
reduce the probability of context corruption. This packet format
uses a large set of flags to provide information about which
fields are present in the packet format and can therefore be of
very varied size. This packet format is similar to the UOR-2-
extension 3 packet format in [RFC3095]
o co_repair: This format is intended to be used when context damage
has been assumed, and therefore changing fields are transmit
uncompressed in this format and contains a complete dynamic chain.
This packet format should be considered a replacement for the IR-
DYN packet format which is not defined for the profiles defined in
this document.
o pt_0_crc3: This packet format only transmits the MSN, and can
therefore only be used to update the MSN and fields that are
derived from the MSN, such as IP-ID and the RTP Timestamp (where
applicable). This packet format is equivalent to the UO-0 packet
format in [RFC3095]
o pt_0_crc7: This packet has the same properties as pt_0_crc3, but
is instead protected by a 7-bit CRC and contains a larger amount
of LSB-encoded MSN bits. This format can for example be used on
ROHC channels that expect a high amount of reordering or link
layers with high residual error rates.
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The following packet format descriptions apply to profiles 0x101 and
0x107.
o pt_1_rnd: This format is a replacement for the UO-1 packet format
in [RFC3095] and can be used to transmit changes in the MSN, RTP
Marker bit and it can update the RTP timestamp using scaled
timestamp encoding.
o pt_1_seq_id: This format is a replacement for the UO-1-ID packet
format in [RFC3095] and can be used to transmit changes in the MSN
and IP-ID.
o pt_1_seq_ts: This format is a replacement for the UO-1-TS packet
format in [RFC3095] and can be used to transmit changes in the
MSN, RTP Marker bit and can update the RTP Timestamp using scaled
timestamp encoding.
o pt_2_rnd: This format is a replacement for the UOR-2 packet format
in [RFC3095] and can be used to transmit changes in the MSN, RTP
Marker bit and the RTP Timestamp, and is protected by a 7-bit CRC.
o pt_2_seq_id: This format is a replacement for the UO-2-ID packet
format in [RFC3095] and can be used to transmit changes in the MSN
and IP-ID. This format is also protected by a 7-bit CRC.
o pt_2_seq_ts: This format is a replacement for the UO-2-TS packet
format in [RFC3095] and can be used to transmit changes in the
MSN, RTP Marker bit and can update the RTP Timestamp using scaled
timestamp encoding. This format is also protected by a 7-bit CRC.
o pt_2_seq_both: This format is replaces the UOR-2-ID extension 1
format in [RFC3095] and can carry changes in both the RTP
Timestamp and IP-ID in addition to the MSN and Marker bit.
The following packet formats descriptions apply to profiles 0x102,
0x103, 0x104 and 0x108.
o pt_1_seq_id: This format is a replacement for the UO-1-ID packet
format in [RFC3095] and can be used to transmit changes in the MSN
and IP-ID.
o pt_2_rnd: This format is a replacement for the UOR-2 packet format
in [RFC3095] and can be used to transmit changes in the MSN and is
protected by a 7-bit CRC.
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o pt_2_seq_id: This format is a replacement for the UO-2-ID packet
format in [RFC3095] and can be used to transmit changes in the MSN
and IP-ID. This format is also protected by a 7-bit CRC.
6.8.2.2. co_repair Header Format
The ROHCv2 co_repair packet has the following format:
0 1 2 3 4 5 6 7
--- --- --- --- --- --- --- ---
: Add-CID octet : if for small CIDs and CID 1-15
+---+---+---+---+---+---+---+---+
| 1 1 1 1 1 0 1 1 | discriminator
+---+---+---+---+---+---+---+---+
: :
/ 0, 1, or 2 octets of CID / 1-2 octets if large CIDs
: :
+---+---+---+---+---+---+---+---+
|r1 | CRC-7 |
+---+---+---+---+---+---+---+---+
| r2 | CRC-3 |
+---+---+---+---+---+---+---+---+
| |
/ Dynamic chain / variable length
| |
- - - - - - - - - - - - - - - -
| |
/ Payload / variable length
| |
- - - - - - - - - - - - - - - -
r1: MUST be set to zero; otherwise, the decompressor MUST discard
the packet.
CRC-7: A 7-bit CRC over the entire uncompressed header, computed
using the crc7(data_value, data_length) encoding method defined in
Section 6.8.2.4, where data_value corresponds to the entire
uncompressed header chain and data_length the length of this
header chain.
r2: MUST be set to zero; otherwise, the decompressor MUST discard
the packet.
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CRC-3: See Section 6.6.11.
Dynamic chain: See Section 6.5.
Payload: The payload of the corresponding original packet, if any.
The payload consists of all data after the last octet of the last
header compressed by the current profile. The presence of a
payload is inferred from the packet length.
6.8.2.3. General CO Header Format
The CO packets communicate irregularities in the packet header. All
CO packets carry a CRC and can update the context. All CO formats
except for co_repair which is defined in Section 6.8.2.2 use the
general format defined in this section.
The general format for a compressed header is as follows:
0 1 2 3 4 5 6 7
--- --- --- --- --- --- --- ---
: Add-CID octet : if for small CIDs and CID 1-15
+---+---+---+---+---+---+---+---+
| first octet of base header | (with type indication)
+---+---+---+---+---+---+---+---+
: :
/ 0, 1, or 2 octets of CID / 1-2 octets if large CIDs
: :
+---+---+---+---+---+---+---+---+
/ remainder of base header / variable number of octets
+---+---+---+---+---+---+---+---+
: :
/ Irregular Chain / variable
: :
--- --- --- --- --- --- --- ---
The base header in the figure above is the compressed representation
of the innermost IP header and other header(s), if any, in the
uncompressed packet.
The entire set of base headers are defined in Section 6.8.2.4 using
the ROHC Formal notation [RFC4997] .
6.8.2.4. Header Formats in ROHC-FN
////////////////////////////////////////////
// Constants
////////////////////////////////////////////
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// IP-ID behavior constants
IP_ID_BEHAVIOR_SEQUENTIAL = 0;
IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED = 1;
IP_ID_BEHAVIOR_RANDOM = 2;
IP_ID_BEHAVIOR_ZERO = 3;
// UDP-lite checksum coverage behavior constants
UDP_LITE_COVERAGE_INFERRED = 0;
UDP_LITE_COVERAGE_STATIC = 1;
UDP_LITE_COVERAGE_IRREGULAR = 2;
UDP_LITE_COVERAGE_RESERVED = 3;
// Variable reordering offset
REORDERING_NONE = 0;
REORDERING_QUARTER = 1;
REORDERING_HALF = 2;
REORDERING_THREEQUARTERS = 3;
// Profile names and versions
PROFILE_RTP_0101 = 0x0101;
PROFILE_UDP_0102 = 0x0102;
PROFILE_ESP_0103 = 0x0103;
PROFILE_IP_0104 = 0x0104;
PROFILE_RTP_0107 = 0x0107; // With UDP-LITE
PROFILE_UDPLITE_0108 = 0x0108; // Without RTP
// Default values for RTP timestamp encoding
TS_STRIDE_DEFAULT = 160;
TIME_STRIDE_DEFAULT = 0;
////////////////////////////////////////////
// Global control fields
////////////////////////////////////////////
CONTROL {
msn [ 16 ];
reorder_ratio [ 2 ];
ip_id_offset [ 16 ]; // Used if innermost IP is IPv4
}
///////////////////////////////////////////////
// Encoding methods not specified in FN syntax:
///////////////////////////////////////////////
baseheader_extension_headers "defined in Section 6.6.1";
baseheader_outer_headers "defined in Section 6.6.2";
control_crc3_encoding "defined in Section 6.6.11";
inferred_ip_v4_header_checksum "defined in Section 6.6.4";
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inferred_ip_v4_length "defined in Section 6.6.6";
inferred_ip_v6_length "defined in Section 6.6.7";
inferred_mine_header_checksum "defined in Section 6.6.5";
inferred_scaled_field "defined in Section 6.6.10";
inferred_sequential_ip_id "defined in Section 6.6.12";
inferred_udp_length "defined in Section 6.6.3";
list_csrc(cc_value) "defined in Section 6.6.13";
timer_based_lsb(time_stride, k, p) "defined in Section 6.6.9";
////////////////////////////////////////////
// General encoding methods
////////////////////////////////////////////
reorder_choice
{
UNCOMPRESSED {
ratio [ 2 ];
}
DEFAULT {
ratio =:= irregular(2);
}
COMPRESSED none {
ENFORCE(ratio.UVALUE == REORDERING_NONE);
ratio [ 2 ];
}
COMPRESSED quarter {
ENFORCE(ratio.UVALUE == REORDERING_QUARTER);
ratio [ 2 ];
}
COMPRESSED half {
ENFORCE(ratio.UVALUE == REORDERING_HALF);
ratio [ 2 ];
}
COMPRESSED three_quarters {
ENFORCE(ratio.UVALUE == REORDERING_THREEQUARTERS);
ratio [ 2 ];
}
}
static_or_irreg(flag, width)
{
UNCOMPRESSED {
field [ width ];
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}
COMPRESSED irreg_enc {
ENFORCE(flag == 1);
field =:= irregular(width) [ width ];
}
COMPRESSED static_enc {
ENFORCE(flag == 0);
field =:= static [ 0 ];
}
}
optional_32(flag)
{
UNCOMPRESSED {
item [ 0, 32 ];
}
COMPRESSED present {
ENFORCE(flag == 1);
item =:= irregular(32) [ 32 ];
}
COMPRESSED not_present {
ENFORCE(flag == 0);
item =:= compressed_value(0, 0) [ 0 ];
}
}
// Send the entire value, or keep previous value
sdvl_or_static(flag)
{
UNCOMPRESSED {
field [ 32 ];
}
COMPRESSED present_7bit {
ENFORCE(flag == 1);
ENFORCE(field.UVALUE < 2^7);
ENFORCE(field.CVALUE == field.UVALUE);
discriminator =:= '0' [ 1 ];
field [ 7 ];
}
COMPRESSED present_14bit {
ENFORCE(flag == 1);
ENFORCE(field.UVALUE < 2^14);
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ENFORCE(field.CVALUE == field.UVALUE);
discriminator =:= '10' [ 2 ];
field [ 14 ];
}
COMPRESSED present_21bit {
ENFORCE(flag == 1);
ENFORCE(field.UVALUE < 2^21);
ENFORCE(field.CVALUE == field.UVALUE);
discriminator =:= '110' [ 3 ];
field [ 21 ];
}
COMPRESSED present_28bit {
ENFORCE(flag == 1);
ENFORCE(field.UVALUE < 2^28);
ENFORCE(field.CVALUE == field.UVALUE);
discriminator =:= '1110' [ 4 ];
field [ 28 ];
}
COMPRESSED present_32bit {
ENFORCE(flag == 1);
ENFORCE(field.CVALUE == field.UVALUE);
discriminator =:= '11111111' [ 8 ];
field [ 32 ];
}
COMPRESSED not_present {
ENFORCE(flag == 0);
field =:= static;
}
}
// Send the entire value, or revert to default value
sdvl_or_default(flag, default_value)
{
UNCOMPRESSED {
field [ 32 ];
}
COMPRESSED present_7bit {
ENFORCE(flag == 1);
ENFORCE(field.UVALUE < 2^7);
ENFORCE(field.CVALUE == field.UVALUE);
discriminator =:= '0' [ 1 ];
field [ 7 ];
}
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COMPRESSED present_14bit {
ENFORCE(flag == 1);
ENFORCE(field.UVALUE < 2^14);
ENFORCE(field.CVALUE == field.UVALUE);
discriminator =:= '10' [ 2 ];
field [ 14 ];
}
COMPRESSED present_21bit {
ENFORCE(flag == 1);
ENFORCE(field.UVALUE < 2^21);
ENFORCE(field.CVALUE == field.UVALUE);
discriminator =:= '110' [ 3 ];
field [ 21 ];
}
COMPRESSED present_28bit {
ENFORCE(flag == 1);
ENFORCE(field.UVALUE < 2^28);
ENFORCE(field.CVALUE == field.UVALUE);
discriminator =:= '1110' [ 4 ];
field [ 28 ];
}
COMPRESSED present_32bit {
ENFORCE(flag == 1);
ENFORCE(field.CVALUE == field.UVALUE);
discriminator =:= '11111111' [ 8 ];
field [ 32 ];
}
COMPRESSED not_present {
ENFORCE(flag == 0);
field =:= uncompressed_value(32, default_value);
}
}
lsb_7_or_31
{
UNCOMPRESSED {
item [ 32 ];
}
COMPRESSED lsb_7 {
discriminator =:= '0' [ 1 ];
item =:= lsb(7, ((2^7) / 4) - 1) [ 7 ];
}
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COMPRESSED lsb_31 {
discriminator =:= '1' [ 1 ];
item =:= lsb(31, ((2^31) / 4) - 1) [ 31 ];
}
}
crc3(data_value, data_length)
{
UNCOMPRESSED {
}
COMPRESSED {
crc_value =:= crc(3, 0x06, 0x07, data_value, data_length) [ 3 ];
}
}
crc7(data_value, data_length)
{
UNCOMPRESSED {
}
COMPRESSED {
crc_value =:= crc(7, 0x79, 0x7f, data_value, data_length) [ 7 ];
}
}
// Encoding method for updating a scaled field and its associated
// control fields. Should be used both when the value is scaled
// or unscaled in a compressed format.
field_scaling(stride_value, scaled_value, unscaled_value)
{
UNCOMPRESSED {
residue_field [ 32 ];
}
COMPRESSED no_scaling {
ENFORCE(stride_value == 0);
ENFORCE(residue_field.UVALUE == unscaled_value);
ENFORCE(scaled_value == 0);
}
COMPRESSED scaling_used {
ENFORCE(stride_value != 0);
ENFORCE(residue_field.UVALUE == (unscaled_value % stride_value));
ENFORCE(unscaled_value ==
scaled_value * stride_value + residue_field.UVALUE);
}
}
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////////////////////////////////////////////
// IPv6 Destination options header
////////////////////////////////////////////
ip_dest_opt
{
UNCOMPRESSED {
next_header [ 8 ];
length [ 8 ];
value [ length.UVALUE * 64 + 48 ];
}
DEFAULT {
length =:= static;
next_header =:= static;
value =:= static;
}
COMPRESSED dest_opt_static {
next_header =:= irregular(8) [ 8 ];
length =:= irregular(8) [ 8 ];
}
COMPRESSED dest_opt_dynamic {
value =:=
irregular(length.UVALUE * 64 + 48) [ length.UVALUE * 64 + 48 ];
}
COMPRESSED dest_opt_irregular {
}
}
////////////////////////////////////////////
// IPv6 Hop-by-Hop options header
////////////////////////////////////////////
ip_hop_opt
{
UNCOMPRESSED {
next_header [ 8 ];
length [ 8 ];
value [ length.UVALUE * 64 + 48 ];
}
DEFAULT {
length =:= static;
next_header =:= static;
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value =:= static;
}
COMPRESSED hop_opt_static {
next_header =:= irregular(8) [ 8 ];
length =:= irregular(8) [ 8 ];
}
COMPRESSED hop_opt_dynamic {
value =:=
irregular(length.UVALUE*64+48) [ length.UVALUE * 64 + 48 ];
}
COMPRESSED hop_opt_irregular {
}
}
////////////////////////////////////////////
// IPv6 Routing header
////////////////////////////////////////////
ip_rout_opt
{
UNCOMPRESSED {
next_header [ 8 ];
length [ 8 ];
value [ length.UVALUE * 64 + 48 ];
}
DEFAULT {
length =:= static;
next_header =:= static;
value =:= static;
}
COMPRESSED rout_opt_static {
next_header =:= irregular(8) [ 8 ];
length =:= irregular(8) [ 8 ];
value =:=
irregular(length.UVALUE*64+48) [ length.UVALUE * 64 + 48 ];
}
COMPRESSED rout_opt_dynamic {
}
COMPRESSED rout_opt_irregular {
}
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}
////////////////////////////////////////////
// GRE Header
////////////////////////////////////////////
optional_lsb_7_or_31(flag)
{
UNCOMPRESSED {
item [ 0, 32 ];
}
COMPRESSED present {
ENFORCE(flag == 1);
item =:= lsb_7_or_31 [ 8, 32 ];
}
COMPRESSED not_present {
ENFORCE(flag == 0);
item =:= compressed_value(0, 0) [ 0 ];
}
}
optional_checksum(flag_value)
{
UNCOMPRESSED {
value [ 0, 16 ];
reserved1 [ 0, 16 ];
}
COMPRESSED cs_present {
ENFORCE(flag_value == 1);
value =:= irregular(16) [ 16 ];
reserved1 =:= uncompressed_value(16, 0) [ 0 ];
}
COMPRESSED not_present {
ENFORCE(flag_value == 0);
value =:= compressed_value(0, 0) [ 0 ];
reserved1 =:= compressed_value(0, 0) [ 0 ];
}
}
gre_proto
{
UNCOMPRESSED {
protocol [ 16 ];
}
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COMPRESSED ether_v4 {
discriminator =:= compressed_value(1, 0) [ 1 ];
protocol =:= uncompressed_value(16, 0x0800) [ 0 ];
}
COMPRESSED ether_v6 {
discriminator =:= compressed_value(1, 1) [ 1 ];
protocol =:= uncompressed_value(16, 0x86DD) [ 0 ];
}
}
gre
{
UNCOMPRESSED {
c_flag [ 1 ];
r_flag =:= uncompressed_value(1, 0) [ 1 ];
k_flag [ 1 ];
s_flag [ 1 ];
reserved0 =:= uncompressed_value(9, 0) [ 9 ];
version =:= uncompressed_value(3, 0) [ 3 ];
protocol [ 16 ];
checksum_and_res [ 0, 32 ];
key [ 0, 32 ];
sequence_number [ 0, 32 ];
}
DEFAULT {
c_flag =:= static;
k_flag =:= static;
s_flag =:= static;
protocol =:= static;
key =:= static;
sequence_number =:= static;
}
COMPRESSED gre_static {
protocol =:= gre_proto [ 1 ];
c_flag =:= irregular(1) [ 1 ];
k_flag =:= irregular(1) [ 1 ];
s_flag =:= irregular(1) [ 1 ];
padding =:= compressed_value(4, 0) [ 4 ];
key =:= optional_32(k_flag.UVALUE) [ 0, 32 ];
}
COMPRESSED gre_dynamic {
checksum_and_res =:=
optional_checksum(c_flag.UVALUE) [ 0, 16 ];
sequence_number =:= optional_32(s_flag.UVALUE) [ 0, 32 ];
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}
COMPRESSED gre_irregular {
checksum_and_res =:= optional_checksum(c_flag.UVALUE) [ 0, 16 ];
sequence_number =:=
optional_lsb_7_or_31(s_flag.UVALUE) [ 0, 8, 32 ];
}
}
/////////////////////////////////////////////
// MINE header
/////////////////////////////////////////////
mine
{
UNCOMPRESSED {
next_header [ 8 ];
s_bit [ 1 ];
res_bits [ 7 ];
checksum [ 16 ];
orig_dest [ 32 ];
orig_src [ 0, 32 ];
}
DEFAULT {
next_header =:= static;
s_bit =:= static;
res_bits =:= static;
checksum =:= inferred_mine_header_checksum;
orig_dest =:= static;
orig_src =:= static;
}
COMPRESSED mine_static {
next_header =:= irregular(8) [ 8 ];
s_bit =:= irregular(1) [ 1 ];
// Reserved bits are included to achieve byte-alignment
res_bits =:= irregular(7) [ 7 ];
orig_dest =:= irregular(32) [ 32 ];
orig_src =:= optional_32(s_bit.UVALUE) [ 0, 32 ];
}
COMPRESSED mine_dynamic {
}
COMPRESSED mine_irregular {
}
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}
/////////////////////////////////////////////
// Authentication Header (AH)
/////////////////////////////////////////////
ah
{
UNCOMPRESSED {
next_header [ 8 ];
length [ 8 ];
res_bits =:= uncompressed_value(16, 0) [ 16 ];
spi [ 32 ];
sequence_number [ 32 ];
icv [ length.UVALUE*32-32 ];
}
DEFAULT {
next_header =:= static;
length =:= static;
spi =:= static;
sequence_number =:= static;
}
COMPRESSED ah_static {
next_header =:= irregular(8) [ 8 ];
length =:= irregular(8) [ 8 ];
spi =:= irregular(32) [ 32 ];
}
COMPRESSED ah_dynamic {
sequence_number =:= irregular(32) [ 32 ];
icv =:=
irregular(length.UVALUE*32-32) [ length.UVALUE*32-32 ];
}
COMPRESSED ah_irregular {
sequence_number =:= lsb_7_or_31 [ 8, 32 ];
icv =:=
irregular(length.UVALUE*32-32) [ length.UVALUE*32-32 ];
}
}
/////////////////////////////////////////////
// ESP header (NULL encrypted)
/////////////////////////////////////////////
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// The value of the next header field from the trailer
// part of the packet is passed as a parameter.
esp_null(next_header_value)
{
UNCOMPRESSED {
spi [ 32 ];
sequence_number [ 32 ];
}
CONTROL {
nh_field [ 8 ];
}
DEFAULT {
spi =:= static;
sequence_number =:= static;
nh_field =:= static;
}
COMPRESSED esp_static {
nh_field =:= compressed_value(8, next_header_value) [ 8 ];
spi =:= irregular(32) [ 32 ];
}
COMPRESSED esp_dynamic {
sequence_number =:= irregular(32) [ 32 ];
}
COMPRESSED esp_irregular {
sequence_number =:= lsb_7_or_31 [ 8, 32 ];
}
}
/////////////////////////////////////////////
// IPv6 Header
/////////////////////////////////////////////
fl_enc
{
UNCOMPRESSED {
flow_label [ 20 ];
}
COMPRESSED fl_zero {
discriminator =:= '0' [ 1 ];
flow_label =:= uncompressed_value(20, 0) [ 0 ];
reserved =:= '0000' [ 4 ];
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}
COMPRESSED fl_non_zero {
discriminator =:= '1' [ 1 ];
flow_label =:= irregular(20) [ 20 ];
}
}
ipv6(profile, is_innermost, outer_ip_flag)
{
UNCOMPRESSED {
version =:= uncompressed_value(4, 6) [ 4 ];
tos_tc [ 8 ];
flow_label [ 20 ];
payload_length [ 16 ];
next_header [ 8 ];
ttl_hopl [ 8 ];
src_addr [ 128 ];
dst_addr [ 128 ];
}
DEFAULT {
tos_tc =:= static;
flow_label =:= static;
payload_length =:= inferred_ip_v6_length;
next_header =:= static;
ttl_hopl =:= static;
src_addr =:= static;
dst_addr =:= static;
}
COMPRESSED ipv6_static {
version_flag =:= '1' [ 1 ];
reserved =:= '00' [ 2 ];
flow_label =:= fl_enc [ 5, 21 ];
next_header =:= irregular(8) [ 8 ];
src_addr =:= irregular(128) [ 128 ];
dst_addr =:= irregular(128) [ 128 ];
}
COMPRESSED ipv6_endpoint_static {
ENFORCE((is_innermost == 1) &&
(profile == PROFILE_IP_0104));
version_flag =:= '1' [ 1 ];
innermost_indicator =:= compressed_value(1, 1) [ 1 ];
reserved =:= '0' [ 1 ];
flow_label =:= fl_enc [ 5, 21 ];
next_header =:= irregular(8) [ 8 ];
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src_addr =:= irregular(128) [ 128 ];
dst_addr =:= irregular(128) [ 128 ];
}
COMPRESSED ipv6_endpoint_dynamic {
ENFORCE((is_innermost == 1) &&
(profile == PROFILE_IP_0104));
tos_tc =:= irregular(8) [ 8 ];
ttl_hopl =:= irregular(8) [ 8 ];
reserved =:= compressed_value(6, 0) [ 6 ];
reorder_ratio =:= reorder_choice [ 2 ];
msn =:= irregular(16) [ 16 ];
}
COMPRESSED ipv6_regular_dynamic {
ENFORCE((is_innermost == 0) ||
(profile != PROFILE_IP_0104));
tos_tc =:= irregular(8) [ 8 ];
ttl_hopl =:= irregular(8) [ 8 ];
}
COMPRESSED ipv6_outer_irregular {
ENFORCE(is_innermost == 0);
tos_tc =:=
static_or_irreg(outer_ip_flag, 8) [ 0, 8 ];
ttl_hopl =:=
static_or_irreg(outer_ip_flag, 8) [ 0, 8 ];
}
COMPRESSED ipv6_innermost_irregular {
ENFORCE(is_innermost == 1);
}
}
/////////////////////////////////////////////
// IPv4 Header
/////////////////////////////////////////////
ip_id_enc_dyn(behavior)
{
UNCOMPRESSED {
ip_id [ 16 ];
}
COMPRESSED ip_id_seq {
ENFORCE((behavior == IP_ID_BEHAVIOR_SEQUENTIAL) ||
(behavior == IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED));
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ENFORCE(ip_id_offset.UVALUE == ip_id.UVALUE - msn.UVALUE);
ip_id =:= irregular(16) [ 16 ];
}
COMPRESSED ip_id_random {
ENFORCE(behavior == IP_ID_BEHAVIOR_RANDOM);
ip_id =:= irregular(16) [ 16 ];
}
COMPRESSED ip_id_zero {
ENFORCE(behavior == IP_ID_BEHAVIOR_ZERO);
ip_id =:= uncompressed_value(16, 0) [ 0 ];
}
}
ip_id_enc_irreg(behavior)
{
UNCOMPRESSED {
ip_id [ 16 ];
}
COMPRESSED ip_id_seq {
ENFORCE(behavior == IP_ID_BEHAVIOR_SEQUENTIAL);
}
COMPRESSED ip_id_seq_swapped {
ENFORCE(behavior == IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED);
}
COMPRESSED ip_id_rand {
ENFORCE(behavior == IP_ID_BEHAVIOR_RANDOM);
ip_id =:= irregular(16) [ 16 ];
}
COMPRESSED ip_id_zero {
ENFORCE(behavior == IP_ID_BEHAVIOR_ZERO);
ip_id =:= uncompressed_value(16, 0) [ 0 ];
}
}
ip_id_behavior_choice(is_inner)
{
UNCOMPRESSED {
behavior [ 2 ];
}
DEFAULT {
behavior =:= irregular(2);
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}
COMPRESSED sequential {
ENFORCE(is_inner == 1);
ENFORCE(behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL);
behavior [ 2 ];
}
COMPRESSED sequential_swapped {
ENFORCE(is_inner == 1);
ENFORCE(behavior.UVALUE ==
IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED);
behavior [ 2 ];
}
COMPRESSED random {
ENFORCE(behavior.UVALUE == IP_ID_BEHAVIOR_RANDOM);
behavior [ 2 ];
}
COMPRESSED zero {
ENFORCE(behavior.UVALUE == IP_ID_BEHAVIOR_ZERO);
behavior [ 2 ];
}
}
ipv4(profile, is_innermost, outer_ip_flag)
{
UNCOMPRESSED {
version =:= uncompressed_value(4, 4) [ 4 ];
hdr_length =:= uncompressed_value(4, 5) [ 4 ];
tos_tc [ 8 ];
length =:= inferred_ip_v4_length [ 16 ];
ip_id [ 16 ];
rf =:= uncompressed_value(1, 0) [ 1 ];
df [ 1 ];
mf =:= uncompressed_value(1, 0) [ 1 ];
frag_offset =:= uncompressed_value(13, 0) [ 13 ];
ttl_hopl [ 8 ];
protocol [ 8 ];
checksum =:= inferred_ip_v4_header_checksum [ 16 ];
src_addr [ 32 ];
dst_addr [ 32 ];
}
CONTROL {
ip_id_behavior [ 2 ];
}
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DEFAULT {
tos_tc =:= static;
df =:= static;
ttl_hopl =:= static;
protocol =:= static;
src_addr =:= static;
dst_addr =:= static;
ip_id_behavior =:= static;
}
COMPRESSED ipv4_static {
version_flag =:= '0' [ 1 ];
reserved =:= '0000000' [ 7 ];
protocol =:= irregular(8) [ 8 ];
src_addr =:= irregular(32) [ 32 ];
dst_addr =:= irregular(32) [ 32 ];
}
COMPRESSED ipv4_endpoint_static {
ENFORCE((is_innermost == 1) &&
(profile == PROFILE_IP_0104));
version_flag =:= '0' [ 1 ];
innermost_indicator =:= compressed_value(1, 1) [ 1 ];
reserved =:= '000000' [ 6 ];
protocol =:= irregular(8) [ 8 ];
src_addr =:= irregular(32) [ 32 ];
dst_addr =:= irregular(32) [ 32 ];
}
COMPRESSED ipv4_endpoint_dynamic {
ENFORCE((is_innermost == 1) &&
(profile == PROFILE_IP_0104));
reserved =:= '000' [ 3 ];
reorder_ratio =:= reorder_choice [ 2 ];
df =:= irregular(1) [ 1 ];
ip_id_behavior =:= ip_id_behavior_choice(is_innermost) [ 2 ];
tos_tc =:= irregular(8) [ 8 ];
ttl_hopl =:= irregular(8) [ 8 ];
ip_id =:= ip_id_enc_dyn(ip_id_behavior.UVALUE) [ 0, 16 ];
msn =:= irregular(16) [ 16 ];
}
COMPRESSED ipv4_regular_dynamic {
ENFORCE((is_innermost == 0) ||
(profile != PROFILE_IP_0104));
reserved =:= '00000' [ 5 ];
df =:= irregular(1) [ 1 ];
ip_id_behavior =:= ip_id_behavior_choice(is_innermost) [ 2 ];
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tos_tc =:= irregular(8) [ 8 ];
ttl_hopl =:= irregular(8) [ 8 ];
ip_id =:= ip_id_enc_dyn(ip_id_behavior.UVALUE) [ 0, 16 ];
}
COMPRESSED ipv4_outer_irregular {
ENFORCE(is_innermost == 0);
ip_id =:= ip_id_enc_irreg(ip_id_behavior.UVALUE) [ 0, 16 ];
tos_tc =:= static_or_irreg(outer_ip_flag, 8) [ 0, 8 ];
ttl_hopl =:= static_or_irreg(outer_ip_flag, 8) [ 0, 8 ];
}
COMPRESSED ipv4_innermost_irregular {
ip_id =:= ip_id_enc_irreg(ip_id_behavior.UVALUE) [ 0, 16 ];
ENFORCE(is_innermost == 1);
}
}
/////////////////////////////////////////////
// UDP Header
/////////////////////////////////////////////
udp(profile)
{
UNCOMPRESSED {
ENFORCE((profile == PROFILE_RTP_0101) ||
(profile == PROFILE_UDP_0102));
src_port [ 16 ];
dst_port [ 16 ];
udp_length =:= inferred_udp_length [ 16 ];
checksum [ 16 ];
}
CONTROL {
checksum_used [ 1 ];
}
DEFAULT {
src_port =:= static;
dst_port =:= static;
}
COMPRESSED udp_static {
src_port =:= irregular(16) [ 16 ];
dst_port =:= irregular(16) [ 16 ];
}
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COMPRESSED udp_endpoint_dynamic {
ENFORCE(profile == PROFILE_UDP_0102);
ENFORCE(checksum_used.UVALUE == (checksum.UVALUE != 0));
checksum =:= irregular(16) [ 16 ];
msn =:= irregular(16) [ 16 ];
reserved =:= compressed_value(6, 0) [ 6 ];
reorder_ratio =:= reorder_choice [ 2 ];
}
COMPRESSED udp_regular_dynamic {
ENFORCE(profile == PROFILE_RTP_0101);
ENFORCE(checksum_used == (checksum.UVALUE != 0));
checksum =:= irregular(16) [ 16 ];
}
COMPRESSED udp_zero_checksum_irregular {
ENFORCE(checksum_used.UVALUE == 0);
checksum =:= uncompressed_value(16, 0) [ 0 ];
}
COMPRESSED udp_with_checksum_irregular {
ENFORCE(checksum_used.UVALUE == 1);
checksum =:= irregular(16) [ 16 ];
}
}
/////////////////////////////////////////////
// RTP Header
/////////////////////////////////////////////
csrc_list_dynchain(presence, cc_value)
{
UNCOMPRESSED {
csrc_list;
}
COMPRESSED no_list {
ENFORCE(cc_value == 0);
ENFORCE(presence == 0);
csrc_list =:= uncompressed_value(0, 0) [ 0 ];
}
COMPRESSED list_present {
ENFORCE(presence == 1);
csrc_list =:= list_csrc(cc_value) [ VARIABLE ];
}
}
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rtp(profile, ts_stride_value, time_stride_value)
{
UNCOMPRESSED {
ENFORCE((profile == PROFILE_RTP_0101) ||
(profile == PROFILE_RTP_0107));
rtp_version =:= uncompressed_value(2, 0) [ 2 ];
pad_bit [ 1 ];
extension [ 1 ];
cc [ 4 ];
marker [ 1 ];
payload_type [ 7 ];
sequence_number [ 16 ];
timestamp [ 32 ];
ssrc [ 32 ];
csrc_list [ cc.UVALUE * 32 ];
}
CONTROL {
ENFORCE(time_stride_value == time_stride.UVALUE);
ENFORCE(ts_stride_value == ts_stride.UVALUE);
ts_stride [ 32 ];
time_stride [ 32 ];
ts_scaled [ 32 ];
ts_offset =:=
field_scaling(ts_stride.UVALUE, ts_scaled.UVALUE,
timestamp.UVALUE) [ 32 ];
}
INITIAL {
ts_stride =:= uncompressed_value(32, TS_STRIDE_DEFAULT);
time_stride =:= uncompressed_value(32, TIME_STRIDE_DEFAULT);
}
DEFAULT {
ENFORCE(msn.UVALUE == sequence_number.UVALUE);
pad_bit =:= static;
extension =:= static;
cc =:= static;
marker =:= static;
payload_type =:= static;
sequence_number =:= static;
timestamp =:= static;
ssrc =:= static;
csrc_list =:= static;
}
COMPRESSED rtp_static {
ssrc =:= irregular(32) [ 32 ];
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}
COMPRESSED rtp_dynamic {
reserved =:= compressed_value(1, 0) [ 1 ];
reorder_ratio =:= reorder_choice [ 2 ];
list_present =:= irregular(1) [ 1 ];
tss_indicator =:= irregular(1) [ 1 ];
tis_indicator =:= irregular(1) [ 1 ];
pad_bit =:= irregular(1) [ 1 ];
extension =:= irregular(1) [ 1 ];
marker =:= irregular(1) [ 1 ];
payload_type =:= irregular(7) [ 7 ];
sequence_number =:= irregular(16) [ 16 ];
timestamp =:= irregular(32) [ 32 ];
ts_stride =:= sdvl_or_default(tss_indicator,
TS_STRIDE_DEFAULT) [ VARIABLE ];
time_stride =:= sdvl_or_default(tis_indicator,
TIME_STRIDE_DEFAULT) [ VARIABLE ];
csrc_list =:=
csrc_list_dynchain(list_present, cc.UVALUE) [ VARIABLE ];
}
COMPRESSED rtp_irregular {
}
}
/////////////////////////////////////////////
// UDP-Lite Header
/////////////////////////////////////////////
checksum_coverage_dynchain(behavior)
{
UNCOMPRESSED {
checksum_coverage [ 16 ];
}
COMPRESSED inferred_coverage {
ENFORCE(behavior == UDP_LITE_COVERAGE_INFERRED);
checksum_coverage =:= inferred_udp_length [ 0 ];
}
COMPRESSED static_coverage {
ENFORCE(behavior == UDP_LITE_COVERAGE_STATIC);
checksum_coverage =:= irregular(16) [ 16 ];
}
COMPRESSED irregular_coverage {
ENFORCE(behavior == UDP_LITE_COVERAGE_IRREGULAR);
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checksum_coverage =:= irregular(16) [ 16 ];
}
}
checksum_coverage_irregular(behavior)
{
UNCOMPRESSED {
checksum_coverage [ 16 ];
}
COMPRESSED inferred_coverage {
ENFORCE(behavior == UDP_LITE_COVERAGE_INFERRED);
checksum_coverage =:= inferred_udp_length [ 0 ];
}
COMPRESSED static_coverage {
ENFORCE(behavior == UDP_LITE_COVERAGE_STATIC);
checksum_coverage =:= static [ 0 ];
}
COMPRESSED irregular_coverage {
ENFORCE(behavior == UDP_LITE_COVERAGE_IRREGULAR);
checksum_coverage =:= irregular(16) [ 16 ];
}
}
udp_lite(profile)
{
UNCOMPRESSED {
ENFORCE((profile == PROFILE_RTP_0107) ||
(profile == PROFILE_UDPLITE_0108));
src_port [ 16 ];
dst_port [ 16 ];
checksum_coverage [ 16 ];
checksum [ 16 ];
}
CONTROL {
coverage_behavior [ 2 ];
}
DEFAULT {
src_port =:= static;
dst_port =:= static;
}
COMPRESSED udp_lite_static {
src_port =:= irregular(16) [ 16 ];
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dst_port =:= irregular(16) [ 16 ];
}
COMPRESSED udp_lite_endpoint_dynamic {
ENFORCE(profile == PROFILE_UDPLITE_0108);
reserved =:= compressed_value(4, 0) [ 4 ];
coverage_behavior =:= irregular(2) [ 2 ];
reorder_ratio =:= reorder_choice [ 2 ];
checksum_coverage =:=
checksum_coverage_dynchain(coverage_behavior.UVALUE) [ 16 ];
checksum =:= irregular(16) [ 16 ];
msn =:= irregular(16) [ 16 ];
}
COMPRESSED udp_lite_regular_dynamic {
coverage_behavior =:= irregular(2) [ 2 ];
reserved =:= compressed_value(6, 0) [ 6 ];
checksum_coverage =:=
checksum_coverage_dynchain(coverage_behavior.UVALUE) [ 16 ];
checksum =:= irregular(16) [ 16 ];
}
COMPRESSED udp_lite_irregular {
checksum_coverage =:=
checksum_coverage_irregular(coverage_behavior.UVALUE) [ 0, 16 ];
checksum =:= irregular(16) [ 16 ];
}
}
/////////////////////////////////////////////
// ESP Header (Non-NULL encrypted
// i.e. only used for the ESP profile)
/////////////////////////////////////////////
esp(profile)
{
UNCOMPRESSED {
ENFORCE(profile == PROFILE_ESP_0103);
ENFORCE(msn.UVALUE == sequence_number.UVALUE % 65536);
spi [ 32 ];
sequence_number [ 32 ];
}
DEFAULT {
spi =:= static;
sequence_number =:= static;
}
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COMPRESSED esp_static {
// Needs to be discriminated from ESP NULL headers,
// and therefore we have a dummy protocol field here.
discriminator =:= uncompressed_value(8, 255) [ 8 ];
spi =:= irregular(32) [ 32 ];
}
COMPRESSED esp_dynamic {
sequence_number =:= irregular(32) [ 32 ];
reserved =:= compressed_value(6, 0) [ 6 ];
reorder_ratio =:= reorder_choice [ 2 ];
}
COMPRESSED esp_irregular {
}
}
///////////////////////////////////////////////////
// Encoding methods used in the profiles' CO packets
///////////////////////////////////////////////////
// Variable reordering offset used for MSN
msn_lsb(k)
{
UNCOMPRESSED {
master [ VARIABLE ];
}
COMPRESSED none {
ENFORCE(reorder_ratio.UVALUE == REORDERING_NONE);
master =:= lsb(k, 1);
}
COMPRESSED quarter {
ENFORCE(reorder_ratio.UVALUE == REORDERING_QUARTER);
master =:= lsb(k, ((2^k) / 4) - 1);
}
COMPRESSED half {
ENFORCE(reorder_ratio.UVALUE == REORDERING_HALF);
master =:= lsb(k, ((2^k) / 2) - 1);
}
COMPRESSED threequarters {
ENFORCE(reorder_ratio.UVALUE == REORDERING_THREEQUARTERS);
master =:= lsb(k, (((2^k) * 3) / 4) - 1);
}
}
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ip_id_lsb(behavior, k)
{
UNCOMPRESSED {
ip_id [ 16 ];
}
CONTROL {
ip_id_nbo [ 16 ];
}
COMPRESSED nbo {
ENFORCE(behavior == IP_ID_BEHAVIOR_SEQUENTIAL);
ENFORCE(ip_id_offset.UVALUE == ip_id.UVALUE - msn.UVALUE);
ip_id_offset =:= lsb(k, ((2^k) / 4) - 1) [ k ];
}
COMPRESSED non_nbo {
ENFORCE(behavior == IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED);
ENFORCE(ip_id_nbo.UVALUE ==
(ip_id.UVALUE / 256) + (ip_id.UVALUE % 256) * 256);
ENFORCE(ip_id_nbo.ULENGTH == 16);
ENFORCE(ip_id_offset.UVALUE == ip_id_nbo.UVALUE - msn.UVALUE);
ip_id_offset =:= lsb(k, ((2^k) / 4) - 1) [ k ];
}
}
ip_id_sequential_variable(behavior, indicator)
{
UNCOMPRESSED {
ip_id [ 16 ];
}
COMPRESSED short {
ENFORCE((behavior == IP_ID_BEHAVIOR_SEQUENTIAL) ||
(behavior == IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED));
ENFORCE(indicator == 0);
ip_id =:= ip_id_lsb(behavior, 8) [ 8 ];
}
COMPRESSED long {
ENFORCE((behavior == IP_ID_BEHAVIOR_SEQUENTIAL) ||
(behavior == IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED));
ENFORCE(indicator == 1);
ENFORCE(ip_id_offset.UVALUE == ip_id.UVALUE - msn.UVALUE);
ip_id =:= irregular(16) [ 16 ];
}
COMPRESSED not_present {
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ENFORCE((behavior == IP_ID_BEHAVIOR_RANDOM) ||
(behavior == IP_ID_BEHAVIOR_ZERO));
}
}
dont_fragment(version)
{
UNCOMPRESSED {
df [ 1 ];
}
COMPRESSED v4 {
ENFORCE(version == 4);
df =:= irregular(1) [ 1 ];
}
COMPRESSED v6 {
ENFORCE(version == 6);
unused =:= compressed_value(1, 0) [ 1 ];
}
}
pt_irr_or_static(flag)
{
UNCOMPRESSED {
payload_type [ 7 ];
}
COMPRESSED not_present {
ENFORCE(flag == 0);
payload_type =:= static [ 0 ];
}
COMPRESSED present {
ENFORCE(flag == 1);
reserved =:= compressed_value(1, 0) [ 1 ];
payload_type =:= irregular(7) [ 7 ];
}
}
csrc_list_presence(presence, cc_value)
{
UNCOMPRESSED {
csrc_list;
}
COMPRESSED no_list {
ENFORCE(presence == 0);
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csrc_list =:= static [ 0 ];
}
COMPRESSED list_present {
ENFORCE(presence == 1);
csrc_list =:= list_csrc(cc_value) [ VARIABLE ];
}
}
scaled_ts_lsb(time_stride_value, k)
{
UNCOMPRESSED {
timestamp [ 32 ];
}
COMPRESSED timerbased {
ENFORCE(time_stride_value != 0);
timestamp =:= timer_based_lsb(time_stride_value, k,
((2^k) / 4) - 1);
}
COMPRESSED regular {
ENFORCE(time_stride_value == 0);
timestamp =:= lsb(k, ((2^k) / 4) - 1);
}
}
// Self-describing variable length encoding with reordering offset
sdvl_sn_lsb(field_width) {
UNCOMPRESSED {
field [ field_width ];
}
COMPRESSED lsb7 {
discriminator =:= '0' [ 1 ];
field =:= msn_lsb(7) [ 7 ];
}
COMPRESSED lsb14 {
discriminator =:= '10' [ 2 ];
field =:= msn_lsb(14) [ 14 ];
}
COMPRESSED lsb21 {
discriminator =:= '110' [ 3 ];
field =:= msn_lsb(21) [ 21 ];
}
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COMPRESSED lsb28 {
discriminator =:= '1110' [ 4 ];
field =:= msn_lsb(28) [ 28 ];
}
COMPRESSED lsb32 {
discriminator =:= '11111111' [ 8 ];
field =:= irregular(field_width) [ field_width ];
}
}
// Self-describing variable length encoding
sdvl_lsb(field_width)
{
UNCOMPRESSED {
field [ field_width ];
}
COMPRESSED lsb7 {
discriminator =:= '0' [ 1 ];
field =:= lsb(7, ((2^7) / 4) - 1) [ 7 ];
}
COMPRESSED lsb14 {
discriminator =:= '10' [ 2 ];
field =:= lsb(14, ((2^14) / 4) - 1) [ 14 ];
}
COMPRESSED lsb21 {
discriminator =:= '110' [ 3 ];
field =:= lsb(21, ((2^21) / 4) - 1) [ 21 ];
}
COMPRESSED lsb28 {
discriminator =:= '1110' [ 4 ];
field =:= lsb(28, ((2^28) / 4) - 1) [ 28 ];
}
COMPRESSED lsb32 {
discriminator =:= '11111111' [ 8 ];
field =:= irregular(field_width) [ field_width ];
}
}
variable_scaled_timestamp(tss_flag, tsc_flag, ts_stride)
{
UNCOMPRESSED {
timestamp [ 32 ];
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}
COMPRESSED present {
ENFORCE((tss_flag == 0) && (tsc_flag == 1));
ENFORCE(ts_stride != 0);
timestamp =:= sdvl_lsb(32) [ VARIABLE ];
}
COMPRESSED not_present {
ENFORCE(((tss_flag == 1) && (tsc_flag == 0)) ||
((tss_flag == 0) && (tsc_flag == 0)));
}
}
variable_unscaled_timestamp(tss_flag, tsc_flag)
{
UNCOMPRESSED {
timestamp [ 32 ];
}
COMPRESSED present {
ENFORCE(((tss_flag == 1) && (tsc_flag == 0)) ||
((tss_flag == 0) && (tsc_flag == 0)));
timestamp =:= sdvl_lsb(32);
}
COMPRESSED not_present {
ENFORCE((tss_flag == 0) && (tsc_flag == 1));
}
}
profile_1_7_flags1_enc(flag)
{
UNCOMPRESSED {
ip_outer_indicator [ 1 ];
ttl_hopl_indicator [ 1 ];
tos_tc_indicator [ 1 ];
df [ 1 ];
ip_id_behavior [ 2 ];
reorder_ratio [ 2 ];
}
COMPRESSED not_present {
ENFORCE(flag == 0);
ENFORCE(ip_outer_indicator.CVALUE == 0);
ENFORCE(ttl_hopl_indicator.CVALUE == 0);
ENFORCE(tos_tc_indicator.CVALUE == 0);
df =:= static;
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ip_id_behavior =:= static;
reorder_ratio =:= static;
}
COMPRESSED present {
ENFORCE(flag == 1);
ip_outer_indicator =:= irregular(1) [ 1 ];
ttl_hopl_indicator =:= irregular(1) [ 1 ];
tos_tc_indicator =:= irregular(1) [ 1 ];
df =:= dont_fragment(ip_version) [ 1 ];
ip_id_behavior =:= ip_id_behavior_choice(1) [ 2 ];
reorder_ratio =:= reorder_choice [ 2 ];
}
}
profile_1_flags2_enc(flag, ip_version)
{
UNCOMPRESSED {
list_indicator [ 1 ];
pt_indicator [ 1 ];
pad_bit [ 1 ];
extension [ 1 ];
time_stride_indicator [ 1 ];
}
COMPRESSED not_present{
ENFORCE(flag == 0);
ENFORCE(list_indicator.UVALUE == 0);
ENFORCE(pt_indicator.UVALUE == 0);
ENFORCE(time_stride_indicator.UVALUE == 0);
pad_bit =:= static;
extension =:= static;
}
COMPRESSED present {
ENFORCE(flag == 1);
list_indicator =:= irregular(1) [ 1 ];
pt_indicator =:= irregular(1) [ 1 ];
time_stride_indicator =:= irregular(1) [ 1 ];
pad_bit =:= irregular(1) [ 1 ];
extension =:= irregular(1) [ 1 ];
reserved =:= compressed_value(3, 0) [ 3 ];
}
}
profile_2_3_4_flags_enc(flag, ip_version)
{
UNCOMPRESSED {
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ip_outer_indicator [ 1 ];
df [ 1 ];
ip_id_behavior [ 2 ];
}
COMPRESSED not_present {
ENFORCE(flag == 0);
ENFORCE(ip_outer_indicator.CVALUE == 0);
df =:= static;
ip_id_behavior =:= static;
}
COMPRESSED present {
ENFORCE(flag == 1);
ip_outer_indicator =:= irregular(1) [ 1 ];
df =:= dont_fragment(ip_version) [ 1 ];
ip_id_behavior =:= ip_id_behavior_choice(1) [ 2 ];
reserved =:= compressed_value(4, 0) [ 4 ];
}
}
profile_8_flags_enc(flag, ip_version)
{
UNCOMPRESSED {
ip_outer_indicator [ 1 ];
df [ 1 ];
ip_id_behavior [ 2 ];
coverage_behavior [ 2 ];
}
COMPRESSED not_present {
ENFORCE(flag == 0);
ENFORCE(ip_outer_indicator.CVALUE == 0);
df =:= static;
ip_id_behavior =:= static;
coverage_behavior =:= static;
}
COMPRESSED present {
ENFORCE(flag == 1);
reserved =:= compressed_value(2, 0) [ 2 ];
ip_outer_indicator =:= irregular(1) [ 1 ];
df =:= dont_fragment(ip_version) [ 1 ];
ip_id_behavior =:= ip_id_behavior_choice(1) [ 2 ];
coverage_behavior =:= irregular(2) [ 2 ];
}
}
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profile_7_flags2_enc(flag, ip_version)
{
UNCOMPRESSED {
list_indicator [ 1 ];
pt_indicator [ 1 ];
time_stride_indicator [ 1 ];
pad_bit [ 1 ];
extension [ 1 ];
coverage_behavior [ 2 ];
}
COMPRESSED not_present{
ENFORCE(flag == 0);
ENFORCE(list_indicator.CVALUE == 0);
ENFORCE(pt_indicator.CVALUE == 0);
ENFORCE(time_stride_indicator.CVALUE == 0);
pad_bit =:= static;
extension =:= static;
coverage_behavior =:= static;
}
COMPRESSED present {
ENFORCE(flag == 1);
reserved =:= compressed_value(1, 0) [ 1 ];
list_indicator =:= irregular(1) [ 1 ];
pt_indicator =:= irregular(1) [ 1 ];
time_stride_indicator =:= irregular(1) [ 1 ];
pad_bit =:= irregular(1) [ 1 ];
extension =:= irregular(1) [ 1 ];
coverage_behavior =:= irregular(2) [ 2 ];
}
}
////////////////////////////////////////////
// RTP profile
////////////////////////////////////////////
rtp_baseheader(profile, ts_stride_value, time_stride_value,
outer_ip_flag)
{
UNCOMPRESSED v4 {
ENFORCE(msn.UVALUE == sequence_number.UVALUE);
outer_headers =:= baseheader_outer_headers [ VARIABLE ];
ip_version =:= uncompressed_value(4, 4) [ 4 ];
header_length =:= uncompressed_value(4, 5) [ 4 ];
tos_tc [ 8 ];
length =:= inferred_ip_v4_length [ 16 ];
ip_id [ 16 ];
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rf =:= uncompressed_value(1, 0) [ 1 ];
df [ 1 ];
mf =:= uncompressed_value(1, 0) [ 1 ];
frag_offset =:= uncompressed_value(13, 0) [ 13 ];
ttl_hopl [ 8 ];
next_header [ 8 ];
ip_checksum =:= inferred_ip_v4_header_checksum [ 16 ];
src_addr [ 32 ];
dest_addr [ 32 ];
extension_headers =:= baseheader_extension_headers [ VARIABLE ];
src_port [ 16 ];
dst_port [ 16 ];
udp_length =:= inferred_udp_length [ 16 ];
udp_checksum [ 16 ];
rtp_version =:= uncompressed_value(2, 2) [ 2 ];
pad_bit [ 1 ];
extension [ 1 ];
cc [ 4 ];
marker [ 1 ];
payload_type [ 7 ];
sequence_number [ 16 ];
timestamp [ 32 ];
ssrc [ 32 ];
csrc_list [ VARIABLE ];
}
UNCOMPRESSED v6 {
ENFORCE(ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_RANDOM);
ENFORCE(msn.UVALUE == sequence_number.UVALUE);
outer_headers =:= baseheader_outer_headers [ VARIABLE ];
ip_version =:= uncompressed_value(4, 6) [ 4 ];
tos_tc [ 8 ];
flow_label [ 20 ];
payload_length =:= inferred_ip_v6_length [ 16 ];
next_header [ 8 ];
ttl_hopl [ 8 ];
src_addr [ 128 ];
dest_addr [ 128 ];
extension_headers =:= baseheader_extension_headers [ VARIABLE ];
src_port [ 16 ];
dst_port [ 16 ];
udp_length =:= inferred_udp_length [ 16 ];
udp_checksum [ 16 ];
rtp_version =:= uncompressed_value(2, 2) [ 2 ];
pad_bit [ 1 ];
extension [ 1 ];
cc [ 4 ];
marker [ 1 ];
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payload_type [ 7 ];
sequence_number [ 16 ];
timestamp [ 32 ];
ssrc [ 32 ];
csrc_list [ VARIABLE ];
df =:= uncompressed_value(0,0) [ 0 ];
ip_id =:= uncompressed_value(0,0) [ 0 ];
}
CONTROL {
ENFORCE(time_stride.UVALUE == time_stride_value);
ENFORCE(ts_stride.UVALUE == ts_stride_value);
ENFORCE(profile == PROFILE_RTP_0101);
ts_stride [ 32 ];
time_stride [ 32 ];
ts_scaled [ 32 ];
ts_offset =:= field_scaling(ts_stride.UVALUE, ts_scaled.UVALUE,
timestamp.UVALUE) [ 32 ];
ip_id_behavior [ 2 ];
}
INITIAL {
ts_stride =:= uncompressed_value(32, TS_STRIDE_DEFAULT);
time_stride =:= uncompressed_value(32, TIME_STRIDE_DEFAULT);
}
DEFAULT {
ENFORCE(outer_ip_flag == 0);
tos_tc =:= static;
dest_addr =:= static;
ttl_hopl =:= static;
src_addr =:= static;
df =:= static;
ip_id_behavior =:= static;
flow_label =:= static;
next_header =:= static;
src_port =:= static;
dst_port =:= static;
pad_bit =:= static;
extension =:= static;
cc =:= static;
// When marker not present in packets, it is assumed 0
marker =:= uncompressed_value(1, 0);
payload_type =:= static;
sequence_number =:= static;
timestamp =:= static;
ssrc =:= static;
csrc_list =:= static;
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}
// Replacement for UOR-2-ext3
COMPRESSED co_common {
ENFORCE(outer_ip_flag == outer_ip_indicator.CVALUE);
discriminator =:= '11111010' [ 8 ];
marker =:= irregular(1) [ 1 ];
header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ];
flags1_indicator =:= irregular(1) [ 1 ];
flags2_indicator =:= irregular(1) [ 1 ];
tsc_indicator =:= irregular(1) [ 1 ];
tss_indicator =:= irregular(1) [ 1 ];
ip_id_indicator =:= irregular(1) [ 1 ];
control_crc3 =:= control_crc3_encoding [ 3 ];
outer_ip_indicator : ttl_hopl_indicator :
tos_tc_indicator : ip_id_behavior : reorder_ratio =:=
profile_1_7_flags1_enc(flags1_indicator.CVALUE) [ 0, 8 ];
list_indicator : pt_indicator : tis_indicator :pad_bit :
extension : df =:= profile_1_flags2_enc(flags2_indicator.CVALUE,
ip_version.UVALUE) [ 0, 8 ];
tos_tc =:= static_or_irreg(tos_tc_indicator.CVALUE, 8) [ 0, 8 ];
ttl_hopl =:= static_or_irreg(ttl_hopl_indicator.CVALUE,
ttl_hopl.ULENGTH) [ 0, 8 ];
payload_type =:= pt_irr_or_static(pt_indicator) [ 0, 8 ];
sequence_number =:=
sdvl_sn_lsb(sequence_number.ULENGTH) [ VARIABLE ];
ip_id =:= ip_id_sequential_variable(ip_id_behavior.UVALUE,
ip_id_indicator.CVALUE) [ 0, 8, 16 ];
ts_scaled =:= variable_scaled_timestamp(tss_indicator.CVALUE,
tsc_indicator, ts_stride.UVALUE) [ VARIABLE ];
timestamp =:= variable_unscaled_timestamp(tss_indicator.CVALUE,
tsc_indicator) [ VARIABLE ];
ts_stride =:= sdvl_or_static(tss_indicator.CVALUE) [ VARIABLE ];
time_stride =:= sdvl_or_static(tis_indicator.CVALUE) [ VARIABLE ];
csrc_list =:= csrc_list_presence(list_indicator.CVALUE,
cc.UVALUE) [ VARIABLE ];
}
// UO-0
COMPRESSED pt_0_crc3 {
discriminator =:= '0' [ 1 ];
msn =:= msn_lsb(4) [ 4 ];
header_crc =:= crc3(THIS.UVALUE, THIS.ULENGTH) [ 3 ];
timestamp =:= inferred_scaled_field [ 0 ];
ip_id =:= inferred_sequential_ip_id [ 0 ];
}
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// New format, Type 0 with strong CRC and more SN bits
COMPRESSED pt_0_crc7 {
discriminator =:= '1000' [ 4 ];
msn =:= msn_lsb(5) [ 5 ];
header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ];
timestamp =:= inferred_scaled_field [ 0 ];
ip_id =:= inferred_sequential_ip_id [ 0 ];
}
// UO-1 replacement
COMPRESSED pt_1_rnd {
ENFORCE(ts_stride.UVALUE != 0);
ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_RANDOM) ||
(ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_ZERO));
discriminator =:= '101' [ 3 ];
msn =:= msn_lsb(4) [ 4 ];
marker =:= irregular(1) [ 1 ];
ts_scaled =:= scaled_ts_lsb(time_stride.UVALUE, 5) [ 5 ];
header_crc =:= crc3(THIS.UVALUE, THIS.ULENGTH) [ 3 ];
}
// UO-1-ID replacement
COMPRESSED pt_1_seq_id {
ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL) ||
(ip_id_behavior.UVALUE ==
IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED));
discriminator =:= '1001' [ 4 ];
ip_id =:= ip_id_lsb(ip_id_behavior.UVALUE, 4) [ 4 ];
msn =:= msn_lsb(5) [ 5 ];
header_crc =:= crc3(THIS.UVALUE, THIS.ULENGTH) [ 3 ];
timestamp =:= inferred_scaled_field [ 0 ];
}
// UO-1-TS replacement
COMPRESSED pt_1_seq_ts {
ENFORCE(ts_stride.UVALUE != 0);
ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL) ||
(ip_id_behavior.UVALUE ==
IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED));
discriminator =:= '101' [ 3 ];
marker =:= irregular(1) [ 1 ];
msn =:= msn_lsb(4) [ 4 ];
ts_scaled =:= scaled_ts_lsb(time_stride.UVALUE, 5) [ 5 ];
header_crc =:= crc3(THIS.UVALUE, THIS.ULENGTH) [ 3 ];
}
// UOR-2 replacement
COMPRESSED pt_2_rnd {
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ENFORCE(ts_stride.UVALUE != 0);
ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_RANDOM) ||
(ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_ZERO));
discriminator =:= '110' [ 3 ];
msn =:= msn_lsb(7) [ 7 ];
ts_scaled =:= scaled_ts_lsb(time_stride.UVALUE, 6) [ 6 ];
marker =:= irregular(1) [ 1 ];
header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ];
}
// UOR-2-ID replacement
COMPRESSED pt_2_seq_id {
ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL) ||
(ip_id_behavior.UVALUE ==
IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED));
discriminator =:= '11000' [ 5 ];
msn =:= msn_lsb(7) [ 7 ];
ip_id =:= ip_id_lsb(ip_id_behavior.UVALUE, 5) [ 5 ];
header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ];
timestamp =:= inferred_scaled_field [ 0 ];
}
// UOR-2-ID-ext1 replacement (both TS and IP-ID)
COMPRESSED pt_2_seq_both {
ENFORCE(ts_stride.UVALUE != 0);
ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL) ||
(ip_id_behavior.UVALUE ==
IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED));
discriminator =:= '11001' [ 5 ];
msn =:= msn_lsb(7) [ 7 ];
ip_id =:= ip_id_lsb(ip_id_behavior.UVALUE, 5) [ 5 ];
header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ];
ts_scaled =:= scaled_ts_lsb(time_stride.UVALUE, 8) [ 8 ];
}
// UOR-2-TS replacement
COMPRESSED pt_2_seq_ts {
ENFORCE(ts_stride.UVALUE != 0);
ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL) ||
(ip_id_behavior.UVALUE ==
IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED));
discriminator =:= '1101' [ 4 ];
msn =:= msn_lsb(7) [ 7 ];
ts_scaled =:= scaled_ts_lsb(time_stride.UVALUE, 5) [ 5 ];
marker =:= irregular(1) [ 1 ];
header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ];
}
}
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////////////////////////////////////////////
// UDP profile
////////////////////////////////////////////
udp_baseheader(profile, outer_ip_flag)
{
UNCOMPRESSED v4 {
outer_headers =:= baseheader_outer_headers [ VARIABLE ];
ip_version =:= uncompressed_value(4, 4) [ 4 ];
header_length =:= uncompressed_value(4, 5) [ 4 ];
tos_tc [ 8 ];
length =:= inferred_ip_v4_length [ 16 ];
ip_id [ 16 ];
rf =:= uncompressed_value(1, 0) [ 1 ];
df [ 1 ];
mf =:= uncompressed_value(1, 0) [ 1 ];
frag_offset =:= uncompressed_value(13, 0) [ 13 ];
ttl_hopl [ 8 ];
next_header [ 8 ];
ip_checksum =:= inferred_ip_v4_header_checksum [ 16 ];
src_addr [ 32 ];
dest_addr [ 32 ];
extension_headers =:= baseheader_extension_headers [ VARIABLE ];
src_port [ 16 ];
dst_port [ 16 ];
udp_length =:= inferred_udp_length [ 16 ];
udp_checksum [ 16 ];
}
UNCOMPRESSED v6 {
ENFORCE(ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_RANDOM);
outer_headers =:= baseheader_outer_headers [ VARIABLE ];
ip_version =:= uncompressed_value(4, 6) [ 4 ];
tos_tc [ 8 ];
flow_label [ 20 ];
payload_length =:= inferred_ip_v6_length [ 16 ];
next_header [ 8 ];
ttl_hopl [ 8 ];
src_addr [ 128 ];
dest_addr [ 128 ];
extension_headers =:= baseheader_extension_headers [ VARIABLE ];
src_port [ 16 ];
dst_port [ 16 ];
udp_length =:= inferred_udp_length [ 16 ];
udp_checksum [ 16 ];
df =:= uncompressed_value(0,0) [ 0 ];
ip_id =:= uncompressed_value(0,0) [ 0 ];
}
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CONTROL {
ENFORCE(profile == PROFILE_UDP_0102);
ip_id_behavior [ 2 ];
}
DEFAULT {
ENFORCE(outer_ip_flag == 0);
tos_tc =:= static;
dest_addr =:= static;
ip_version =:= static;
ttl_hopl =:= static;
src_addr =:= static;
df =:= static;
ip_id_behavior =:= static;
flow_label =:= static;
next_header =:= static;
src_port =:= static;
dst_port =:= static;
}
// Replacement for UOR-2-ext3
COMPRESSED co_common {
ENFORCE(outer_ip_flag == outer_ip_indicator.CVALUE);
discriminator =:= '11111010' [ 8 ];
ip_id_indicator =:= irregular(1) [ 1 ];
header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ];
flags_indicator =:= irregular(1) [ 1 ];
ttl_hopl_indicator =:= irregular(1) [ 1 ];
tos_tc_indicator =:= irregular(1) [ 1 ];
reorder_ratio =:= reorder_choice [ 2 ];
control_crc3 =:= control_crc3_encoding [ 3 ];
outer_ip_indicator : df : ip_id_behavior =:=
profile_2_3_4_flags_enc(
flags_indicator.CVALUE, ip_version.UVALUE) [ 0, 8 ];
tos_tc =:= static_or_irreg(tos_tc_indicator.CVALUE, 8) [ 0, 8 ];
ttl_hopl =:= static_or_irreg(ttl_hopl_indicator.CVALUE,
ttl_hopl.ULENGTH) [ 0, 8 ];
msn =:= msn_lsb(8) [ 8 ];
ip_id =:= ip_id_sequential_variable(ip_id_behavior.UVALUE,
ip_id_indicator.CVALUE) [ 0, 8, 16 ];
}
// UO-0
COMPRESSED pt_0_crc3 {
discriminator =:= '0' [ 1 ];
msn =:= msn_lsb(4) [ 4 ];
header_crc =:= crc3(THIS.UVALUE, THIS.ULENGTH) [ 3 ];
ip_id =:= inferred_sequential_ip_id [ 0 ];
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}
// New format, Type 0 with strong CRC and more SN bits
COMPRESSED pt_0_crc7 {
discriminator =:= '100' [ 3 ];
msn =:= msn_lsb(6) [ 6 ];
header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ];
ip_id =:= inferred_sequential_ip_id [ 0 ];
}
// UO-1-ID replacement (PT-1 only used for sequential)
COMPRESSED pt_1_seq_id {
ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL) ||
(ip_id_behavior.UVALUE ==
IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED));
discriminator =:= '101' [ 3 ];
header_crc =:= crc3(THIS.UVALUE, THIS.ULENGTH) [ 3 ];
msn =:= msn_lsb(6) [ 6 ];
ip_id =:= ip_id_lsb(ip_id_behavior.UVALUE, 4) [ 4 ];
}
// UOR-2 replacement
COMPRESSED pt_2_rnd {
ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_RANDOM) ||
(ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_ZERO));
discriminator =:= '110' [ 3 ];
msn =:= msn_lsb(6) [ 6 ];
header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ];
}
// UOR-2-ID replacement
COMPRESSED pt_2_seq_id {
ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL) ||
(ip_id_behavior.UVALUE ==
IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED));
discriminator =:= '1100' [ 4 ];
ip_id =:= ip_id_lsb(ip_id_behavior.UVALUE, 5) [ 5 ];
header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ];
msn =:= msn_lsb(8) [ 8 ];
}
}
////////////////////////////////////////////
// ESP profile
////////////////////////////////////////////
esp_baseheader(profile, outer_ip_flag)
{
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UNCOMPRESSED v4 {
ENFORCE(msn.UVALUE == sequence_number.UVALUE % 65536);
outer_headers =:= baseheader_outer_headers [ VARIABLE ];
ip_version =:= uncompressed_value(4, 4) [ 4 ];
header_length =:= uncompressed_value(4, 5) [ 4 ];
tos_tc [ 8 ];
length =:= inferred_ip_v4_length [ 16 ];
ip_id [ 16 ];
rf =:= uncompressed_value(1, 0) [ 1 ];
df [ 1 ];
mf =:= uncompressed_value(1, 0) [ 1 ];
frag_offset =:= uncompressed_value(13, 0) [ 13 ];
ttl_hopl [ 8 ];
next_header [ 8 ];
ip_checksum =:= inferred_ip_v4_header_checksum [ 16 ];
src_addr [ 32 ];
dest_addr [ 32 ];
extension_headers =:= baseheader_extension_headers [ VARIABLE ];
spi [ 32 ];
sequence_number [ 32 ];
}
UNCOMPRESSED v6 {
ENFORCE(msn.UVALUE == (sequence_number.UVALUE % 65536));
ENFORCE(ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_RANDOM);
outer_headers =:= baseheader_outer_headers [ VARIABLE ];
ip_version =:= uncompressed_value(4, 6) [ 4 ];
tos_tc [ 8 ];
flow_label [ 20 ];
payload_length =:= inferred_ip_v6_length [ 16 ];
next_header [ 8 ];
ttl_hopl [ 8 ];
src_addr [ 128 ];
dest_addr [ 128 ];
extension_headers =:= baseheader_extension_headers [ VARIABLE ];
spi [ 32 ];
sequence_number [ 32 ];
df =:= uncompressed_value(0,0) [ 0 ];
ip_id =:= uncompressed_value(0,0) [ 0 ];
}
CONTROL {
ENFORCE(profile == PROFILE_ESP_0103);
ip_id_behavior [ 2 ];
}
DEFAULT {
ENFORCE(outer_ip_indicator == 0);
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tos_tc =:= static;
dest_addr =:= static;
ttl_hopl =:= static;
src_addr =:= static;
df =:= static;
ip_id_behavior =:= static;
flow_label =:= static;
next_header =:= static;
spi =:= static;
sequence_number =:= static;
}
// Replacement for UOR-2-ext3
COMPRESSED co_common {
ENFORCE(outer_ip_flag == outer_ip_indicator.CVALUE);
discriminator =:= '11111010' [ 8 ];
ip_id_indicator =:= irregular(1) [ 1 ];
header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ];
flags_indicator =:= irregular(1) [ 1 ];
ttl_hopl_indicator =:= irregular(1) [ 1 ];
tos_tc_indicator =:= irregular(1) [ 1 ];
reorder_ratio =:= reorder_choice [ 2 ];
control_crc3 =:= control_crc3_encoding [ 3 ];
outer_ip_indicator : df : ip_id_behavior =:=
profile_2_3_4_flags_enc(
flags_indicator.CVALUE, ip_version.UVALUE) [ 0, 8 ];
tos_tc =:= static_or_irreg(tos_tc_indicator.CVALUE, 8) [ 0, 8 ];
ttl_hopl =:= static_or_irreg(ttl_hopl_indicator.CVALUE,
ttl_hopl.ULENGTH) [ 0, 8 ];
sequence_number =:=
sdvl_sn_lsb(sequence_number.ULENGTH) [ VARIABLE ];
ip_id =:= ip_id_sequential_variable(ip_id_behavior.UVALUE,
ip_id_indicator.CVALUE) [ 0, 8, 16 ];
}
// Sequence number sent instead of MSN due to field length
// UO-0
COMPRESSED pt_0_crc3 {
discriminator =:= '0' [ 1 ];
sequence_number =:= msn_lsb(4) [ 4 ];
header_crc =:= crc3(THIS.UVALUE, THIS.ULENGTH) [ 3 ];
ip_id =:= inferred_sequential_ip_id [ 0 ];
}
// New format, Type 0 with strong CRC and more SN bits
COMPRESSED pt_0_crc7 {
discriminator =:= '100' [ 3 ];
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sequence_number =:= msn_lsb(6) [ 6 ];
header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ];
ip_id =:= inferred_sequential_ip_id [ 0 ];
}
// UO-1-ID replacement (PT-1 only used for sequential)
COMPRESSED pt_1_seq_id {
ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL) ||
(ip_id_behavior.UVALUE ==
IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED));
discriminato =:= '101' [ 3 ];
header_crc =:= crc3(THIS.UVALUE, THIS.ULENGTH) [ 3 ];
sequence_number =:= msn_lsb(6) [ 6 ];
ip_id =:= ip_id_lsb(ip_id_behavior.UVALUE, 4) [ 4 ];
}
// UOR-2 replacement
COMPRESSED pt_2_rnd {
ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_RANDOM) ||
(ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_ZERO));
discriminator =:= '110' [ 3 ];
sequence_number =:= msn_lsb(6) [ 6 ];
header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ];
}
// UOR-2-ID replacement
COMPRESSED pt_2_seq_id {
ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL) ||
(ip_id_behavior.UVALUE ==
IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED));
discriminator =:= '1100' [ 4 ];
ip_id =:= ip_id_lsb(ip_id_behavior.UVALUE, 5) [ 5 ];
header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ];
sequence_number =:= msn_lsb(8) [ 8 ];
}
}
////////////////////////////////////////////
// IP-only profile
////////////////////////////////////////////
iponly_baseheader(profile, outer_ip_flag)
{
UNCOMPRESSED v4 {
outer_headers =:= baseheader_outer_headers [ VARIABLE ];
ip_version =:= uncompressed_value(4, 4) [ 4 ];
header_length =:= uncompressed_value(4, 5) [ 4 ];
tos_tc [ 8 ];
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length =:= inferred_ip_v4_length [ 16 ];
ip_id [ 16 ];
rf =:= uncompressed_value(1, 0) [ 1 ];
df [ 1 ];
mf =:= uncompressed_value(1, 0) [ 1 ];
frag_offset =:= uncompressed_value(13, 0) [ 13 ];
ttl_hopl [ 8 ];
next_header [ 8 ];
ip_checksum =:= inferred_ip_v4_header_checksum [ 16 ];
src_addr [ 32 ];
dest_addr [ 32 ];
extension_headers =:= baseheader_extension_headers [ VARIABLE ];
}
UNCOMPRESSED v6 {
ENFORCE(ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_RANDOM);
outer_headers =:= baseheader_outer_headers [ VARIABLE ];
ip_version =:= uncompressed_value(4, 6) [ 4 ];
tos_tc [ 8 ];
flow_label [ 20 ];
payload_length =:= inferred_ip_v6_length [ 16 ];
next_header [ 8 ];
ttl_hopl [ 8 ];
src_addr [ 128 ];
dest_addr [ 128 ];
extension_headers =:= baseheader_extension_headers [ VARIABLE ];
df =:= uncompressed_value(0,0) [ 0 ];
ip_id =:= uncompressed_value(0,0) [ 0 ];
}
CONTROL {
ENFORCE(profile == PROFILE_IP_0104);
ip_id_behavior [ 2 ];
}
DEFAULT {
ENFORCE(outer_ip_indicator == 0);
tos_tc =:= static;
dest_addr =:= static;
ttl_hopl =:= static;
src_addr =:= static;
df =:= static;
ip_id_behavior =:= static;
flow_label =:= static;
next_header =:= static;
}
// Replacement for UOR-2-ext3
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COMPRESSED co_common {
ENFORCE(outer_ip_flag == outer_ip_indicator.CVALUE);
discriminator =:= '11111010' [ 8 ];
ip_id_indicator =:= irregular(1) [ 1 ];
header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ];
flags_indicator =:= irregular(1) [ 1 ];
ttl_hopl_indicator =:= irregular(1) [ 1 ];
tos_tc_indicator =:= irregular(1) [ 1 ];
reorder_ratio =:= reorder_choice [ 2 ];
control_crc3 =:= control_crc3_encoding [ 3 ];
outer_ip_indicator : df : ip_id_behavior =:=
profile_2_3_4_flags_enc(
flags_indicator.CVALUE, ip_version.UVALUE) [ 0, 8 ];
tos_tc =:= static_or_irreg(tos_tc_indicator.CVALUE, 8) [ 0, 8 ];
ttl_hopl =:= static_or_irreg(ttl_hopl_indicator.CVALUE,
ttl_hopl.ULENGTH) [ 0, 8 ];
msn =:= msn_lsb(8) [ 8 ];
ip_id =:= ip_id_sequential_variable(ip_id_behavior.UVALUE,
ip_id_indicator.CVALUE) [ 0, 8, 16 ];
}
// UO-0
COMPRESSED pt_0_crc3 {
discriminator =:= '0' [ 1 ];
msn =:= msn_lsb(4) [ 4 ];
header_crc =:= crc3(THIS.UVALUE, THIS.ULENGTH) [ 3 ];
ip_id =:= inferred_sequential_ip_id [ 0 ];
}
// New format, Type 0 with strong CRC and more SN bits
COMPRESSED pt_0_crc7 {
discriminator =:= '100' [ 3 ];
msn =:= msn_lsb(6) [ 6 ];
header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ];
ip_id =:= inferred_sequential_ip_id [ 0 ];
}
// UO-1-ID replacement (PT-1 only used for sequential)
COMPRESSED pt_1_seq_id {
ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL) ||
(ip_id_behavior.UVALUE ==
IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED));
discriminator =:= '101' [ 3 ];
header_crc =:= crc3(THIS.UVALUE, THIS.ULENGTH) [ 3 ];
msn =:= msn_lsb(6) [ 6 ];
ip_id =:= ip_id_lsb(ip_id_behavior.UVALUE, 4) [ 4 ];
}
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// UOR-2 replacement
COMPRESSED pt_2_rnd {
ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_RANDOM) ||
(ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_ZERO));
discriminator =:= '110' [ 3 ];
msn =:= msn_lsb(6) [ 6 ];
header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ];
}
// UOR-2-ID replacement
COMPRESSED pt_2_seq_id {
ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL) ||
(ip_id_behavior.UVALUE ==
IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED));
discriminator =:= '1100' [ 4 ];
ip_id =:= ip_id_lsb(ip_id_behavior.UVALUE, 5) [ 5 ];
header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ];
msn =:= msn_lsb(8) [ 8 ];
}
}
////////////////////////////////////////////
// UDP-lite/RTP profile
////////////////////////////////////////////
udplite_rtp_baseheader(profile, ts_stride_value, time_stride_value,
outer_ip_flag)
{
UNCOMPRESSED v4 {
ENFORCE(msn.UVALUE == sequence_number.UVALUE);
outer_headers =:= baseheader_outer_headers [ VARIABLE ];
ip_version =:= uncompressed_value(4, 4) [ 4 ];
header_length =:= uncompressed_value(4, 5) [ 4 ];
tos_tc [ 8 ];
length =:= inferred_ip_v4_length [ 16 ];
ip_id [ 16 ];
rf =:= uncompressed_value(1, 0) [ 1 ];
df [ 1 ];
mf =:= uncompressed_value(1, 0) [ 1 ];
frag_offset =:= uncompressed_value(13, 0) [ 13 ];
ttl_hopl [ 8 ];
next_header [ 8 ];
ip_checksum =:= inferred_ip_v4_header_checksum [ 16 ];
src_addr [ 32 ];
dest_addr [ 32 ];
extension_headers =:= baseheader_extension_headers [ VARIABLE ];
src_port [ 16 ];
dst_port [ 16 ];
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checksum_coverage [ 16 ];
udp_checksum [ 16 ];
rtp_version =:= uncompressed_value(2, 2) [ 2 ];
pad_bit [ 1 ];
extension [ 1 ];
cc [ 4 ];
marker [ 1 ];
payload_type [ 7 ];
sequence_number [ 16 ];
timestamp [ 32 ];
ssrc [ 32 ];
csrc_list [ VARIABLE ];
}
UNCOMPRESSED v6 {
ENFORCE(ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_RANDOM);
outer_headers =:= baseheader_outer_headers [ VARIABLE ];
ip_version =:= uncompressed_value(4, 6) [ 4 ];
tos_tc [ 8 ];
flow_label [ 20 ];
payload_length =:= inferred_ip_v6_length [ 16 ];
next_header [ 8 ];
ttl_hopl [ 8 ];
src_addr [ 128 ];
dest_addr [ 128 ];
extension_headers =:= baseheader_extension_headers [ VARIABLE ];
src_port [ 16 ];
dst_port [ 16 ];
checksum_coverage [ 16 ];
udp_checksum [ 16 ];
rtp_version =:= uncompressed_value(2, 2) [ 2 ];
pad_bit [ 1 ];
extension [ 1 ];
cc [ 4 ];
marker [ 1 ];
payload_type [ 7 ];
sequence_number [ 16 ];
timestamp [ 32 ];
ssrc [ 32 ];
csrc_list [ VARIABLE ];
df =:= uncompressed_value(0,0) [ 0 ];
ip_id =:= uncompressed_value(0,0) [ 0 ];
}
CONTROL {
ENFORCE(time_stride.UVALUE == time_stride_value);
ENFORCE(ts_stride.UVALUE == ts_stride_value);
ENFORCE(profile == PROFILE_RTP_0107);
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ip_id_behavior [ 2 ];
coverage_behavior [ 2 ];
ts_stride [ 32 ];
time_stride [ 32 ];
ts_scaled [ 32 ];
ts_offset =:= field_scaling(ts_stride.UVALUE, ts_scaled.UVALUE,
timestamp.UVALUE) [ 32 ];
}
DEFAULT {
ENFORCE(outer_ip_indicator == 0);
tos_tc =:= static;
dest_addr =:= static;
ttl_hopl =:= static;
src_addr =:= static;
df =:= static;
ip_id_behavior =:= static;
flow_label =:= static;
next_header =:= static;
src_port =:= static;
dst_port =:= static;
pad_bit =:= static;
extension =:= static;
cc =:= static;
// When marker not present in packets, it is assumed 0
marker =:= uncompressed_value(1, 0);
payload_type =:= static;
sequence_number =:= static;
timestamp =:= static;
ssrc =:= static;
csrc_list =:= static;
}
// Replacement for UOR-2-ext3
COMPRESSED co_common {
ENFORCE(outer_ip_flag == outer_ip_indicator.CVALUE);
discriminator =:= '11111010' [ 8 ];
marker =:= irregular(1) [ 1 ];
header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ];
flags1_indicator =:= irregular(1) [ 1 ];
flags2_indicator =:= irregular(1) [ 1 ];
tsc_indicator =:= irregular(1) [ 1 ];
tss_indicator =:= irregular(1) [ 1 ];
ip_id_indicator =:= irregular(1) [ 1 ];
control_crc3 =:= control_crc3_encoding [ 3 ];
outer_ip_indicator : ttl_hopl_indicator :
tos_tc_indicator : ip_id_behavior : reorder_ratio =:=
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profile_1_7_flags1_enc(flags1_indicator.CVALUE) [ 0, 8 ];
list_indicator : tis_indicator : pt_indicator : pad_bit :
extension : df : coverage_behavior =:=
profile_7_flags2_enc(flags2_indicator.CVALUE,
ip_version.UVALUE) [ 0, 8 ];
tos_tc =:= static_or_irreg(tos_tc_indicator.CVALUE, 8) [ 0, 8 ];
ttl_hopl =:= static_or_irreg(ttl_hopl_indicator.CVALUE,
ttl_hopl.ULENGTH) [ 0, 8 ];
payload_type =:= pt_irr_or_static(pt_indicator.CVALUE) [ 0, 8 ];
sequence_number =:=
sdvl_sn_lsb(sequence_number.ULENGTH) [ VARIABLE ];
ip_id =:= ip_id_sequential_variable(ip_id_behavior.UVALUE,
ip_id_indicator.CVALUE) [ 0, 8, 16 ];
ts_scaled =:= variable_scaled_timestamp(tss_indicator.CVALUE,
tsc_indicator.CVALUE, ts_stride.UVALUE) [ VARIABLE ];
timestamp =:= variable_unscaled_timestamp(tss_indicator.CVALUE,
tsc_indicator.CVALUE) [ VARIABLE ];
ts_stride =:= sdvl_or_static(tss_indicator.CVALUE) [ VARIABLE ];
time_stride =:= sdvl_or_static(tis_indicator.CVALUE) [ VARIABLE ];
csrc_list =:=
csrc_list_presence(list_indicator.CVALUE,
cc.UVALUE) [ VARIABLE ];
}
// UO-0
COMPRESSED pt_0_crc3 {
discriminator =:= '0' [ 1 ];
msn =:= msn_lsb(4) [ 4 ];
header_crc =:= crc3(THIS.UVALUE, THIS.ULENGTH) [ 3 ];
timestamp =:= inferred_scaled_field [ 0 ];
ip_id =:= inferred_sequential_ip_id [ 0 ];
}
// New format, Type 0 with strong CRC and more SN bits
COMPRESSED pt_0_crc7 {
discriminator =:= '1000' [ 4 ];
msn =:= msn_lsb(5) [ 5 ];
header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ];
timestamp =:= inferred_scaled_field [ 0 ];
ip_id =:= inferred_sequential_ip_id [ 0 ];
}
// UO-1 replacement
COMPRESSED pt_1_rnd {
ENFORCE(ts_stride.UVALUE != 0);
ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_RANDOM) ||
(ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_ZERO));
discriminator =:= '101' [ 3 ];
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msn =:= msn_lsb(4) [ 4 ];
marker =:= irregular(1) [ 1 ];
ts_scaled =:= scaled_ts_lsb(time_stride.UVALUE, 5) [ 5 ];
header_crc =:= crc3(THIS.UVALUE, THIS.ULENGTH) [ 3 ];
}
// UO-1-ID replacement
COMPRESSED pt_1_seq_id {
ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL) ||
(ip_id_behavior.UVALUE ==
IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED));
discriminator =:= '1001' [ 4 ];
ip_id =:= ip_id_lsb(ip_id_behavior.UVALUE, 4) [ 4 ];
msn =:= msn_lsb(5) [ 5 ];
header_crc =:= crc3(THIS.UVALUE, THIS.ULENGTH) [ 3 ];
timestamp =:= inferred_scaled_field [ 0 ];
}
// UO-1-TS replacement
COMPRESSED pt_1_seq_ts {
ENFORCE(ts_stride.UVALUE != 0);
ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL) ||
(ip_id_behavior.UVALUE ==
IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED));
discriminator =:= '101' [ 3 ];
marker =:= irregular(1) [ 1 ];
msn =:= msn_lsb(4) [ 4 ];
ts_scaled =:= scaled_ts_lsb(time_stride.UVALUE, 5) [ 5 ];
header_crc =:= crc3(THIS.UVALUE, THIS.ULENGTH) [ 3 ];
}
// UOR-2 replacement
COMPRESSED pt_2_rnd {
ENFORCE(ts_stride.UVALUE != 0);
ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_RANDOM) ||
(ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_ZERO));
discriminator =:= '110' [ 3 ];
msn =:= msn_lsb(7) [ 7 ];
ts_scaled =:= scaled_ts_lsb(time_stride.UVALUE, 6) [ 6 ];
marker =:= irregular(1) [ 1 ];
header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ];
}
// UOR-2-ID replacement
COMPRESSED pt_2_seq_id {
ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL) ||
(ip_id_behavior.UVALUE ==
IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED));
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discriminator =:= '11000' [ 5 ];
msn =:= msn_lsb(7) [ 7 ];
ip_id =:= ip_id_lsb(ip_id_behavior.UVALUE, 5) [ 5 ];
header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ];
timestamp =:= inferred_scaled_field [ 0 ];
}
// UOR-2-ID-ext1 replacement (both TS and IP-ID)
COMPRESSED pt_2_seq_both {
ENFORCE(ts_stride.UVALUE != 0);
ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL) ||
(ip_id_behavior.UVALUE ==
IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED));
discriminator =:= '11001' [ 5 ];
msn =:= msn_lsb(7) [ 7 ];
ip_id =:= ip_id_lsb(ip_id_behavior.UVALUE, 5) [ 5 ];
header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ];
ts_scaled =:= scaled_ts_lsb(time_stride.UVALUE, 8) [ 8 ];
}
// UOR-2-TS replacement
COMPRESSED pt_2_seq_ts {
ENFORCE(ts_stride.UVALUE != 0);
ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL) ||
(ip_id_behavior.UVALUE ==
IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED));
discriminator =:= '1101' [ 4 ];
msn =:= msn_lsb(7) [ 7 ];
ts_scaled =:= scaled_ts_lsb(time_stride.UVALUE, 5) [ 5 ];
marker =:= irregular(1) [ 1 ];
header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ];
}
}
////////////////////////////////////////////
// UDP-lite profile
////////////////////////////////////////////
udplite_baseheader(profile, outer_ip_flag)
{
UNCOMPRESSED v4 {
outer_headers =:= baseheader_outer_headers [ VARIABLE ];
ip_version =:= uncompressed_value(4, 4) [ 4 ];
header_length =:= uncompressed_value(4, 5) [ 4 ];
tos_tc [ 8 ];
length =:= inferred_ip_v4_length [ 16 ];
ip_id [ 16 ];
rf =:= uncompressed_value(1, 0) [ 1 ];
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df [ 1 ];
mf =:= uncompressed_value(1, 0) [ 1 ];
frag_offset =:= uncompressed_value(13, 0) [ 13 ];
ttl_hopl [ 8 ];
next_header [ 8 ];
ip_checksum =:= inferred_ip_v4_header_checksum [ 16 ];
src_addr [ 32 ];
dest_addr [ 32 ];
extension_headers =:= baseheader_extension_headers [ VARIABLE ];
src_port [ 16 ];
dst_port [ 16 ];
checksum_coverage [ 16 ];
udp_checksum [ 16 ];
}
UNCOMPRESSED v6 {
ENFORCE(ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_RANDOM);
outer_headers =:= baseheader_outer_headers [ VARIABLE ];
ip_version =:= uncompressed_value(4, 6) [ 4 ];
tos_tc [ 8 ];
flow_label [ 20 ];
payload_length =:= inferred_ip_v6_length [ 16 ];
next_header [ 8 ];
ttl_hopl [ 8 ];
src_addr [ 128 ];
dest_addr [ 128 ];
extension_headers =:= baseheader_extension_headers [ VARIABLE ];
src_port [ 16 ];
dst_port [ 16 ];
checksum_coverage [ 16 ];
udp_checksum [ 16 ];
df =:= uncompressed_value(0,0) [ 0 ];
ip_id =:= uncompressed_value(0,0) [ 0 ];
}
CONTROL {
ENFORCE(profile == PROFILE_UDPLITE_0108);
ip_id_behavior [ 2 ];
coverage_behavior [ 2 ];
}
DEFAULT {
ENFORCE(outer_ip_indicator == 0);
tos_tc =:= static;
dest_addr =:= static;
ttl_hopl =:= static;
src_addr =:= static;
df =:= static;
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ip_id_behavior =:= static;
flow_label =:= static;
next_header =:= static;
src_port =:= static;
dst_port =:= static;
}
// Replacement for UOR-2-ext3
COMPRESSED co_common {
ENFORCE(outer_ip_flag == outer_ip_indicator.CVALUE);
discriminator =:= '11111010' [ 8 ];
ip_id_indicator =:= irregular(1) [ 1 ];
header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ];
flags_indicator =:= irregular(1) [ 1 ];
ttl_hopl_indicator =:= irregular(1) [ 1 ];
tos_tc_indicator =:= irregular(1) [ 1 ];
reorder_ratio =:= reorder_choice [ 2 ];
control_crc3 =:= control_crc3_encoding [ 3 ];
outer_ip_indicator : df : ip_id_behavior :
coverage_behavior =:=
profile_8_flags_enc(flags_indicator.CVALUE,
ip_version.UVALUE) [ 0, 8 ];
tos_tc =:= static_or_irreg(tos_tc_indicator.CVALUE, 8) [ 0, 8 ];
ttl_hopl =:= static_or_irreg(ttl_hopl_indicator.CVALUE,
ttl_hopl.ULENGTH) [ 0, 8 ];
msn =:= msn_lsb(8) [ 8 ];
ip_id =:= ip_id_sequential_variable(ip_id_behavior.UVALUE,
ip_id_indicator.CVALUE) [ 0, 8, 16 ];
}
// UO-0
COMPRESSED pt_0_crc3 {
discriminator =:= '0' [ 1 ];
msn =:= msn_lsb(4) [ 4 ];
header_crc =:= crc3(THIS.UVALUE, THIS.ULENGTH) [ 3 ];
ip_id =:= inferred_sequential_ip_id [ 0 ];
}
// New format, Type 0 with strong CRC and more SN bits
COMPRESSED pt_0_crc7 {
discriminator =:= '100' [ 3 ];
msn =:= msn_lsb(6) [ 6 ];
header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ];
ip_id =:= inferred_sequential_ip_id [ 0 ];
}
// UO-1-ID replacement (PT-1 only used for sequential)
COMPRESSED pt_1_seq_id {
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ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL) ||
(ip_id_behavior.UVALUE ==
IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED));
discriminator =:= '101' [ 3 ];
header_crc =:= crc3(THIS.UVALUE, THIS.ULENGTH) [ 3 ];
msn =:= msn_lsb(6) [ 6 ];
ip_id =:= ip_id_lsb(ip_id_behavior.UVALUE, 4) [ 4 ];
}
// UOR-2 replacement
COMPRESSED pt_2_rnd {
ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_RANDOM) ||
(ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_ZERO));
discriminator =:= '110' [ 3 ];
msn =:= msn_lsb(6) [ 6 ];
header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ];
}
// UOR-2-ID replacement
COMPRESSED pt_2_seq_id {
ENFORCE((ip_id_behavior.UVALUE == IP_ID_BEHAVIOR_SEQUENTIAL) ||
(ip_id_behavior.UVALUE ==
IP_ID_BEHAVIOR_SEQUENTIAL_SWAPPED));
discriminator =:= '1100' [ 4 ];
ip_id =:= ip_id_lsb(ip_id_behavior.UVALUE, 5) [ 5 ];
header_crc =:= crc7(THIS.UVALUE, THIS.ULENGTH) [ 7 ];
msn =:= msn_lsb(8) [ 8 ];
}
}
6.9. Feedback Formats and Options
6.9.1. Feedback Formats
This section describes the feedback format for ROHCv2 profiles, using
the formats described in section 5.2.3 of [RFC4995].
The Acknowledgment Number field of the feedback formats contains the
least significant bits of the MSN (see Section 6.3.1) that
corresponds to the reference header that is being acknowledged. A
reference header is a header that has been successfully CRC-8
validated or CRC verified. If there is no reference header
available, the feedback MUST carry an ACKNUMBER-NOT-VALID option.
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FEEDBACK-1
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| Acknowledgment Number |
+---+---+---+---+---+---+---+---+
Acknowledgment Number: The eight least significant bits of the
MSN.
A FEEDBACK-1 is an ACK. In order to send a NACK or a STATIC-NACK,
FEEDBACK-2 must be used.
FEEDBACK-2
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
|Acktype| Acknowledgment Number |
+---+---+---+---+---+---+---+---+
| Acknowledgment Number |
+---+---+---+---+---+---+---+---+
| CRC |
+---+---+---+---+---+---+---+---+
/ Feedback options /
+---+---+---+---+---+---+---+---+
Acktype:
0 = ACK
1 = NACK
2 = STATIC-NACK
3 is reserved (MUST NOT be used for parsability)
Acknowledgment Number: The least significant bits of the MSN.
CRC: 8-bit CRC computed over the entire feedback payload including
any CID fields but excluding the packet type, the 'Size' field and
the 'Code' octet, using the polynomial defined in [RFC4995],
Section 5.3.1.1. If the CID is given with an Add-CID octet, the
Add-CID octet immediately precedes the FEEDBACK-1 or FEEDBACK-2
format. For purposes of computing the CRC, the CRC field is zero.
Feedback options: A variable number of feedback options, see
Section 6.9.2. Options may appear in any order.
A FEEDBACK-2 of type NACK or STATIC-NACK is always implicitely an
acknowlegement for a successfully decompressed packet, which
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corresponds to a packet whose LSBs match the Acknowledgment Number of
the feedback element, unless the ACKNUMBER-NOT-VALID option
Section 6.9.2.2 appears in the feedback element.
The FEEDBACK-2 format always carry a CRC and is thus more robust than
the FEEDBACK-1 format. When receiving FEEDBACK-2, the compressor
MUST verify the information by computing the CRC and comparing the
result with the CRC carried in the feedback format. If the two are
not identical, the feedback element MUST be discarded.
6.9.2. Feedback Options
A feedback option has variable length and the following general
format:
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| Opt Type | Opt Len |
+---+---+---+---+---+---+---+---+
/ option data / Opt Length (octets)
+---+---+---+---+---+---+---+---+
6.9.2.1. The REJECT option
The REJECT option informs the compressor that the decompressor does
not have sufficient resources to handle the flow.
+---+---+---+---+---+---+---+---+
| Opt Type = 2 | Opt Len = 0 |
+---+---+---+---+---+---+---+---+
When receiving a REJECT option, the compressor MUST stop compressing
the packet flow, and SHOULD refrain from attempting to increase the
number of compressed packet flows for some time. The REJECT option
MUST NOT appear more than once in the FEEDBACK-2 format, otherwise
the compressor MUST discard the entire feedback element.
6.9.2.2. The ACKNUMBER-NOT-VALID option
The ACKNUMBER-NOT-VALID option indicates that the Acknowledgment
Number field of the feedback is not valid.
+---+---+---+---+---+---+---+---+
| Opt Type = 3 | Opt Len = 0 |
+---+---+---+---+---+---+---+---+
A compressor MUST NOT use the Acknowledgment Number of the feedback
to find the corresponding sent header when this option is present.
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When this option is used, the Acknowledgment Number field of the
FEEDBACK-2 format is set to zero. Consequently, a NACK or a STATIC-
NACK feedback type sent with the ACKNUMBER-NOT-VALID option is
equivalent to a STATIC-NACK with respect to the type of context
repair requested by the decompressor.
The ACKNUMBER-NOT-VALID option MUST NOT appear more than once in the
FEEDBACK-2 format and MUST NOT appear in the same feedback element as
the MSN option, otherwise the compressor MUST discard the entire
feedback element.
6.9.2.3. The CONTEXT_MEMORY Feedback Option
The CONTEXT_MEMORY option informs the compressor that the
decompressor does not have sufficient memory resources to handle the
context of the packet flow, as the flow is currently compressed.
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| Opt Type = 9 | Opt Len = 0 |
+---+---+---+---+---+---+---+---+
When receiving a CONTEXT_MEMORY option, the compressor SHOULD take
actions to compress the packet flow in a way that requires less
decompressor memory resources, or stop compressing the packet flow.
The CONTEXT_MEMORY option MUST NOT appear more than once in the
FEEDBACK-2 format, otherwise the compressor MUST discard the entire
feedback element.
6.9.2.4. The CLOCK_RESOLUTION Feedback Option
The CLOCK_RESOLUTION option informs the compressor of the clock
resolution of the decompressor. It also informs whether the
decompressor supports timer-based compression of the RTP TS timestamp
(see Section 6.6.9) or not. The CLOCK_RESOLUTION option is
applicable per channel, i.e. it applies to any context associated
with a profile for which the option is relevant between one
compressor and decompressor pair.
+---+---+---+---+---+---+---+---+
| Opt Type = 10 | Opt Len = 1 |
+---+---+---+---+---+---+---+---+
| clock resolution (ms) |
+---+---+---+---+---+---+---+---+
The smallest clock resolution which can be indicated is 1
millisecond. The value zero has a special meaning: it indicates that
the decompressor cannot do timer-based compression of the RTP
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Timestamp. The CLOCK_RESOLUTION option MUST NOT appear more than
once in the FEEDBACK-2 format, otherwise the compressor MUST discard
the entire feedback element.
6.9.2.5. Unknown option types
If an option type other than those defined in this document is
encountered, the compressor MUST discard the entire feedback element.
7. Security Considerations
A malfunctioning or malicious header compressor could cause the
header decompressor to reconstitute packets that do not match the
original packets but still have valid IP, UDP and RTP headers and
possibly also valid UDP checksums. Such corruption may be detected
with end-to-end authentication and integrity mechanisms which will
not be affected by the compression. Moreover, this header
compression scheme uses an internal checksum for verification of
reconstructed headers. This reduces the probability of producing
decompressed headers not matching the original ones without this
being noticed.
Denial-of-service attacks are possible if an intruder can introduce
(for example) bogus IR or FEEDBACK packets onto the link and thereby
cause compression efficiency to be reduced. However, an intruder
having the ability to inject arbitrary packets at the link layer in
this manner raises additional security issues that dwarf those
related to the use of header compression.
8. IANA Considerations
The following ROHC profile identifiers have been reserved by the IANA
for the profiles defined in this document:
Identifier Profile
---------- -------
0x0101 ROHCv2 RTP
0x0102 ROHCv2 UDP
0x0103 ROHCv2 ESP
0x0104 ROHCv2 IP
0x0107 ROHCv2 RTP/UDP-Lite
0x0108 ROHCv2 UDP-Lite
<# Editor's Note: To be removed before publication #>
ROHC profile identifiers must be reserved by the IANA for the updated
profiles defined in this document. A suggested registration in the
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"RObust Header Compression (ROHC) Profile Identifiers" name space
would then be:
Profile Identifier Usage Reference
------------------ ---------------------- ---------
0x0000 ROHC uncompressed RFC 3095
0xnn00 Reserved
0x0001 ROHC RTP RFC 3095
0x0101 ROHCv2 RTP [RFCXXXX (this)]
0xnn01 Reserved
0x0002 ROHC UDP RFC 3095
0x0102 ROHCv2 UDP [RFCXXXX (this)]
0xnn02 Reserved
0x0003 ROHC ESP RFC 3095
0x0103 ROHCv2 ESP [RFCXXXX (this)]
0xnn03 Reserved
0x0004 ROHC IP RFC 3843
0x0104 ROHCv2 IP [RFCXXXX (this)]
0xnn04 Reserved
0x0005 ROHC LLA RFC 4362
0x0105 ROHC LLA with R-mode RFC 3408
0xnn05 Reserved
0x0006 ROHC TCP RFC4996
0xnn06 Reserved
0x0007 ROHC RTP/UDP-Lite RFC 4019
0x0107 ROHCv2 RTP/UDP-Lite [RFCXXXX (this)]
0xnn07 Reserved
0x0008 ROHC UDP-Lite RFC 4019
0x0108 ROHCv2 UDP-Lite [RFCXXXX (this)]
0xnn08 Reserved
0x0009-0xnn7F To be Assigned by IANA
0xnn80-0xnnFE To be Assigned by IANA
0xnnFF Reserved
9. Acknowledgements
The authors would like to thank Carl Knutsson, Haipeng Jin and Rohit
Kapoor for comments and discussions about these profiles. Also
thanks to the many people who have contributed to previous ROHC
specifications.
10. References
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10.1. Normative References
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
August 1980.
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
September 1981.
[RFC2004] Perkins, C., "Minimal Encapsulation within IP", RFC 2004,
October 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, December 1998.
[RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
March 2000.
[RFC2890] Dommety, G., "Key and Sequence Number Extensions to GRE",
RFC 2890, September 2000.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003.
[RFC3828] Larzon, L-A., Degermark, M., Pink, S., Jonsson, L-E., and
G. Fairhurst, "The Lightweight User Datagram Protocol
(UDP-Lite)", RFC 3828, July 2004.
[RFC4019] Pelletier, G., "RObust Header Compression (ROHC): Profiles
for User Datagram Protocol (UDP) Lite", RFC 4019,
April 2005.
[RFC4302] Kent, S., "IP Authentication Header", RFC 4302,
December 2005.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, December 2005.
[RFC4995] Jonsson, L-E., Pelletier, G., and K. Sandlund, "The RObust
Header Compression (ROHC) Framework", RFC 4995, July 2007.
[RFC4997] Finking, R. and G. Pelletier, "Formal Notation for RObust
Header Compression (ROHC-FN)", RFC 4997, July 2007.
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10.2. Informative References
[RFC3095] Bormann, C., Burmeister, C., Degermark, M., Fukushima, H.,
Hannu, H., Jonsson, L-E., Hakenberg, R., Koren, T., Le,
K., Liu, Z., Martensson, A., Miyazaki, A., Svanbro, K.,
Wiebke, T., Yoshimura, T., and H. Zheng, "RObust Header
Compression (ROHC): Framework and four profiles: RTP, UDP,
ESP, and uncompressed", RFC 3095, July 2001.
[RFC3843] Jonsson, L-E. and G. Pelletier, "RObust Header Compression
(ROHC): A Compression Profile for IP", RFC 3843,
June 2004.
[RFC4224] Pelletier, G., Jonsson, L-E., and K. Sandlund, "RObust
Header Compression (ROHC): ROHC over Channels That Can
Reorder Packets", RFC 4224, January 2006.
Appendix A. Detailed classification of header fields
Header compression is possible due to the fact that most header
fields do not vary randomly from packet to packet. Many of the
fields exhibit static behavior or change in a more or less
predictable way. When designing a header compression scheme, it is
of fundamental importance to understand the behavior of the fields in
detail.
In this appendix, all fields in the headers compressible by these
profiles are classified and analyzed. The analysis is based on
behavior for the types of traffic that are expected to be the most
frequently compressed (e.g. RTP field behavior is based on voice
and/or video traffic behavior).
Fields are classified as belonging to one of the following classes:
INFERRED - These fields contain values that can be inferred from
other values, for example the size of the frame carrying the packet,
and thus do not have to be included in compressed packets.
STATIC These fields are expected to be constant throughout the
lifetime of the flow and any change to them only has to be possible
to convey in IR packets.
STATIC-DEF - These fields are expected to be constant throughout the
lifetime of the flow and whose values can be used to define a flow.
They are only sent in IR packets.
STATIC-KNOWN - These fields are expected to have well-known values
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and therefore do not need to be communicated at all.
SEMISTATIC These fields are unchanged most of the time. However,
occasionally the value changes but will revert to its original value.
For ROHCv2, the values of such fields do not need to be possible to
change with the smallest compressed packet formats, but should be
possible to change via slightly larger compressed packets.
RARELY CHANGING (RC) These are fields that change their values
occasionally and then keep their new values. For ROHCv2, the values
of such fields do not need to be possible to change with the smallest
compressed packet formats, but should be possible to change via
slightly larger compressed packets.
IRREGULAR These are the fields for which no useful change pattern can
be identified and should be transmitted uncompressed in all
compressed packets.
PATTERN These field that change between each packet, but change in a
predictable pattern.
Appendix A.1. IPv4 Header Fields
+------------------------+----------------+
| Field | Class |
+------------------------+----------------+
| Version | STATIC-KNOWN |
| Header Length | STATIC-KNOWN |
| Type Of Service | RC |
| Packet Length | INFERRED |
| Identification | |
| Sequential | PATTERN |
| Seq. swap | PATTERN |
| Random | IRREGULAR |
| Zero | STATIC |
| Reserved flag | STATIC-KNOWN |
| Don't Fragment flag | RC |
| More Fragments flag | STATIC-KNOWN |
| Fragment Offset | STATIC-KNOWN |
| Time To Live | RC |
| Protocol | STATIC-DEF |
| Header Checksum | INFERRED |
| Source Address | STATIC-DEF |
| Destination Address | STATIC-DEF |
+------------------------+----------------+
Version
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The version field states which IP version is used, and is set to
the value four.
Header Length
As long no options are present in the IP header, the header length
is constant with the value five. If there are options, the field
could be RC or STATIC-DEF, but only option-less headers are
compressed by ROHCv2 profiles. The field is therefore classified
as STATIC-KNOWN.
Type Of Service
The Type Of Service field is expected to be constant during the
lifetime of a flow or to change relatively seldom.
Packet Length
Information about packet length is expected to be provided by the
link layer. The field is therefore classified as INFERRED.
IPv4 Identification
The Identification field (IP ID) is used to identify what
fragments constitute a datagram when reassembling fragmented
datagrams. The IPv4 specification does not specify exactly how
this field is to be assigned values, only that each packet should
get an IP ID that is unique for the source-destination pair and
protocol for the time the datagram (or any of its fragments) could
be alive in the network. This means that assignment of IP ID
values can be done in various ways, but the expected behaviors
have been separated into four classes.
Sequential
In this behavior, the IP-ID is expected to increment by one for
most packets, but may increment by a value larger than one,
depending on the behavior of the transmitting IPv4 stack.
Sequential Swapped
When using this behavior, the IP-ID behaves as in the
Sequential behavior, but the two bytes of IP-ID are byte
swapped. Therefore, the IP-ID can be swapped before
compression to make it behave exactly as the Sequential
behavior.
Random
Some IP stacks assign IP ID values using a pseudo-random number
generator. There is thus no correlation between the ID values
of subsequent datagrams, and therefore there is no way to
predict the IP ID value for the next datagram. For header
compression purposes, this means that the IP ID field needs to
be sent uncompressed with each datagram, resulting in two extra
octets of header.
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Zero
This behavior, although not a legal implementation of IPv4 is
sometimes seen in existing IPv4 stacks. When this behavior is
used, all IP packets have the IP-ID value set to zero.
Flags
The Reserved flag must be set to zero and is therefore classified
as STATIC-KNOWN. The Don't Fragment (DF) flag will changes rarely
and is therefore classified as RC. Finally, the More Fragments
(MF) flag is expected to be zero because IP fragments will not be
compressed by ROHC and is therefore classified as STATIC-KNOWN.
Fragment Offset
Under the assumption that no fragmentation occurs, the fragment
offset is always zero and is therefore classified as STATIC-KNOWN.
Time To Live
Time To Live field is expected to be constant during the lifetime
of a flow or to alternate between a limited number of values due
to route changes.
Protocol
This field will have the same value in all packets of a flow and
is therefore classified as STATIC-DEF.
Header Checksum
The header checksum protects individual hops from processing a
corrupted header. When almost all IP header information is
compressed away, there is no point in having this additional
checksum; instead it can be regenerated at the decompressor side.
The field is therefore classified as INFERRED.
Source and Destination addresses
These fields are part of the definition of a flow and must thus be
constant for all packets in the flow.
Appendix A.2. IPv6 Header Fields
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+----------------------+----------------+
| Field | Class |
+----------------------+----------------+
| Version | STATIC-KNOWN |
| Traffic Class | RC |
| Flow Label | STATIC-DEF |
| Payload Length | INFERRED |
| Next Header | STATIC-DEF |
| Hop Limit | RC |
| Source Address | STATIC-DEF |
| Destination Address | STATIC-DEF |
+----------------------+----------------+
Version
The version field states which IP version is used, and is set to
the value six.
Traffic Class
The Traffic Class field is expected to be constant during the
lifetime of a flow or to change relatively seldom.
Flow Label
This field may be used to identify packets belonging to a specific
flow. If not used, the value should be set to zero. Otherwise,
all packets belonging to the same flow must have the same value in
this field. The field is therefore classified as STATIC-DEF.
Payload Length
Information about packet length (and, consequently, payload
length) is expected to be provided by the link layer. The field
is therefore classified as INFERRED.
Next Header
This field will have the same value in all packets of a flow and
is therefore classified as STATIC-DEF.
Hop Limit
The Hop Limit field is expected to be constant during the lifetime
of a flow or to alternate between a limited number of values due
to route changes.
Source and Destination addresses
These fields are part of the definition of a flow and must thus be
constant for all packets in the flow. The fields are therefore
classified as STATIC-DEF.
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Appendix A.3. UDP Header Fields
+------------------+-------------+
| Field | Class |
+------------------+-------------+
| Source Port | STATIC-DEF |
| Destination Port | STATIC-DEF |
| Length | INFERRED |
| Checksum | |
| Disabled | STATIC |
| Enabled | IRREGULAR |
+------------------+-------------+
Source and Destination ports
These fields are part of the definition of a flow and must thus be
constant for all packets in the flow.
Length
Information about packet length is expected to be provided by the
link layer. The field is therefore classified as INFERRED.
Checksum
The checksum can be optional. If disabled, its value is
constantly zero and can be compressed away. If enabled, its value
depends on the payload, which for compression purposes is
equivalent to it changing randomly with every packet.
Appendix A.4. UDP-Lite Header Fields
+--------------------+-------------+
| Field | Class |
+--------------------+-------------+
| Source Port | STATIC-DEF |
| Destination Port | STATIC-DEF |
| Checksum Coverage | |
| Zero | STATIC-DEF |
| Constant | INFERRED |
| Variable | IRREGULAR |
| Checksum | IRREGULAR |
+--------------------+-------------+
Source and Destination Port
These fields are part of the definition of a flow and must thus be
constant for all packets in the flow.
Checksum Coverage
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The Checksum Coverage field may behave in different ways: it may
have a value of zero, it may be equal to the datagram length, or
it may have any value between eight octets and the length of the
datagram. From a compression perspective, this field is expected
to either be entirely predictable (for the cases where it follows
the same behavior as the UDP Length field or where it takes on a
constant value) or either to change randomly for each packet
(making the value unpredictable from a header-compression
perspective). For all cases, the behavior itself is not expected
to change for this field during the lifetime of a packet flow, or
to change relatively seldom.
Checksum
The information used for the calculation of the UDP-Lite checksum
is governed by the value of the checksum coverage and minimally
includes the UDP-Lite header. The checksum is a changing field
that must always be sent as-is.
Appendix A.5. RTP Header Fields
+----------------+----------------+
| Field | Class |
+----------------+----------------+
| Version | STATIC-KNOWN |
| Padding | RC |
| Extension | RC |
| CSRC Counter | RC |
| Marker | SEMISTATIC |
| Payload Type | RC |
| Sequence Number| PATTERN |
| Timestamp | PATTERN |
| SSRC | STATIC-DEF |
| CSRC | RC |
+----------------+----------------+
Version
This field is expected to have the value two and the field is
therefore classified as STATIC-KNOWN.
Padding
The use of this field is application-dependent, but when payload
padding is used it is likely to be present in most or all packets.
The field is classified as RC to allow for the case where the
value of this field is changes.
Extension
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If RTP extensions are used by the application, these extensions
are often present in all packets, although the use of extensions
is infrequent. To allow efficient compression of a flow using
extensions in only a few packets, this field is classified as RC.
CSRC Count
This field indicates the number of CSRC items present in the CSRC
list. This number is expected to be mostly constant on a packet-
to-packet basis and when it changes, change by small amounts. As
long as no RTP mixer is used, the value of this field will be
zero.
Marker
For audio, the marker bit should be set only in the first packet
of a talkspurt, while for video it should be set in the last
packet of every picture. This means that in both cases the RTP
marker is classified as SEMISTATIC.
Payload Type
Applications could adapt to congestion by changing payload type
and/or frame sizes, but that is not expected to happen frequently,
so this field is classified as RC.
RTP Sequence Number
The RTP Sequence Number will be incremented by one for each packet
sent.
Timestamp
In the audio case:
As long as there are no pauses in the audio stream, the RTP
Timestamp will be incremented by a constant value,
corresponding to the number of samples in the speech frame. It
will thus mostly follow the RTP Sequence Number. When there
has been a silent period and a new talkspurt begins, the
timestamp will jump in proportion to the length of the silent
period. However, the increment will probably be within a
relatively limited range.
In the video case:
Between two consecutive packets, the timestamp will either be
unchanged or increase by a multiple of a fixed value
corresponding to the picture clock frequency. The timestamp
can also decrease by a multiple of the fixed value for certain
coding schemes. This increase, expressed as a multiple of the
picture clock frequency, is in most cases very limited.
SSRC
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This field is part of the definition of a flow and must thus be
constant for all packets in the flow. The field is therefore
classified as STATIC-DEF.
Contributing Sources (CSRC)
The participants in a session, who are identified by the CSRC
fields, are usually expected to be unchanged on a packet-to-packet
basis, but will infrequently change by a few additions and/or
removals.
Appendix A.6. ESP Header Fields
This classification applies both to the encrypted ESP header used in
profile 0x0103 and the NULL-encrypted ESP header used in all the
profiles of this document.
+------------------+-------------+
| Field | Class |
+------------------+-------------+
| SPI | STATIC-DEF |
| Sequence Number | PATTERN |
+------------------+-------------+
SPI
This field is used to identify a specific flow and only changes
when the sequence number wraps around, and is therefore classified
as STATIC-DEF.
ESP Sequence Number
The ESP Sequence Number will be incremented by one for each packet
sent.
Appendix A.7. IPv6 Extension Header Fields
+-----------------------+---------------+
| Field | Class |
+-----------------------+---------------+
| Next Header | STATIC-DEF |
| Ext Hdr Len | |
| Routing | STATIC-DEF |
| Hop-by-hop | STATIC |
| Destination | STATIC |
| Options | |
| Routing | STATIC-DEF |
| Hop-by-hop | RC |
| Destination | RC |
+-----------------------+---------------+
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Next Header
This field will have the same value in all packets of a flow and
is therefore classified as STATIC-DEF.
Ext Hdr Len
For the Routing header, it is expected that the length remains
constant for the duration of the flow, and a change in the length
should be classified as a new flow by the ROHC compressor. For
Hop-by-hop and Destination options headers, the length is expected
to remain static, but can be updated by an IR packet.
Options
For the Routing header, it is expected that the option content
remains constant for the duration of the flow, and a change in the
routing information should be classified as a new flow by the ROHC
compressor. For Hop-by-hop and Destination options headers, the
options are expected to remain static, but can be updated by an IR
packet.
Appendix A.8. GRE Header Fields
+--------------------+---------------+
| Field | Class |
+--------------------+---------------+
| C flag | STATIC |
| K flag | STATIC |
| S flag | STATIC |
| R flag | STATIC-KNOWN |
| Reserved0, Version | STATIC-KNOWN |
| Protocol | STATIC-DEF |
| Checksum | IRREGULAR |
| Reserved | STATIC-KNOWN |
| Sequence Number | PATTERN |
| Key | STATIC-DEF |
+--------------------+---------------+
Flags
The four flag bits are not expected to change for the duration of
the flow, and the R flag is expected to always be set to zero.
Reserved0, Version
Both these fields are expected to be set to zero for the duration
of any flow.
Protocol
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This field will have the same value in all packets of a flow and
is therefore classified as STATIC-DEF.
Checksum
When the checksum field is present, it is expected to behave
unpredictably.
Reserved
When present, this field is expected to be set to zero.
Sequence Number
When present, the Sequence Number increases by one for each
packet.
Key
When present, the Key field is used to define the flow and does
not change.
Appendix A.9. MINE Header Fields
+---------------------+----------------+
| Field | Class |
+---------------------+----------------+
| Protocol | STATIC-DEF |
| S bit | STATIC-DEF |
| Reserved | STATIC-KNOWN |
| Checksum | INFERRED |
| Source Address | STATIC-DEF |
| Destination Address | STATIC-DEF |
+---------------------+----------------+
Protocol
This field will have the same value in all packets of a flow and
is therefore classified as STATIC-DEF.
S bit
The S bit is not expected to change during a flow.
Reserved
The reserved field is expected to be set to zero.
Checksum
The header checksum protects individual routing hops from
processing a corrupted header. Since all fields of this header
are compressed away, there is no need to include this checksum in
compressed packets and it can be regenerated at the decompressor
side.
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Source and Destination Addresses
These fields can be used to define the flow are not expected to
change.
Appendix A.10. AH Header Fields
+---------------------+----------------+
| Field | Class |
+---------------------+----------------+
| Next Header | STATIC-DEF |
| Payload Length | STATIC |
| Reserved | STATIC-KNOWN |
| SPI | STATIC-DEF |
| Sequence Number | PATTERN |
| ICV | IRREGULAR |
+---------------------+----------------+
Next Header
This field will have the same value in all packets of a flow and
is therefore classified as STATIC-DEF.
Payload Length
It is expected that the length of the header is constant for the
duration of the flow.
Reserved
The value of this field will be set to zero.
SPI
This field is used to identify a specific flow and only changes
when the sequence number wraps around, and is therefore classified
as STATIC-DEF.
Sequence Number
The Sequence Number will be incremented by one for each packet
sent.
ICV
The ICV is expected behave unpredictably and is therefore
classified as IRREGULAR.
Appendix B. Compressor Implementation Guidelines
This section describes some guiding principles for implementing a
ROHCv2 compressor with focus on how to efficiently select appropriate
packet formats. All the text in this appendix should be considered
guidelines and they have no normative impact on how a ROHCv2
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implementation must be realized.
Appendix B.1. Reference Management
The compressor usually maintains a sliding window of reference
headers which contains as many references as needed for the
optimistic approach. Each reference contains a description of which
changes occured in the flow between two consecutive headers in the
flow, and a new reference is inserted into the window each time a
packet is compressed by this context. A reference may for example be
implemented as a stored copy of the uncompressed header being
represented. When the compressor is confident that a specific
reference is no longer used by the decompressor (for example by using
the optimistic approach or feedback received), the reference is
removed from the sliding window.
Appendix B.2. Window-based LSB Encoding (W-LSB)
Section 5.1.1 describes how the optimistic approach impacts the
packet format selection for the compressor. Exactly how the
compressor selects packet format is up to the implementation to
decide, but the following is an example of how this process can be
performed for LSB-encoded fields, though the use of Window-based LSB
encoding (W-LSB).
When using W-LSB encoding, the compressor uses a number of references
from its context decided by its optimistic approach and extracts the
value of the field to be encoded from each reference and finds the
maximum and minimum values. When having obtained these limits, the
compressor assumes that the decompressor is currently using a value
in the range from the minimum to the maximum value (inclusive) as its
reference. The compressor should then select a number of LSBs of the
new value so that these can be decompressed both if the decompressor
has the minimum value or the maximum value as its current reference.
Appendix B.3. W-LSB Encoding and Timer-based Compression
Section 6.6.9 defines decompressor behavior for timer-based RTP
timestamp compression. This section gives guidelines on how the
compressor should select how many bits of timestamp LSBs need to
transmitted. When using timer-based compression, the number of bits
to transmit depend on the amount of jitter both before the compressor
and the jitter between compressor and decompressor. The jitter
before the compressor can be estimated using the following
computation:
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Max_Jitter_BC =
max {|(T_n - T_j) - ((a_n - a_j) / time_stride)|,
for all headers j in the sliding window}
Where (T_n - T_j) is the difference in timestamp between the
currently compressed header and a reference header and (a_n - a_j) is
the difference in arrival time between those same two headers.
In addition to this, the compressor needs to estimate an upper bound
for the jitter between compressor and decompressor (Max_Jitter_CD).
This information may for example come from lower layers, but if such
information is not available, the compressor should use an upper
bound which is significantly higher than the link roundtrip time.
After obtaining estimates for the jitters, the number of bits needed
to transmit is obtained using the following calculation:
ceiling(log2(2 * (Max_Jitter_BC + Max_Jitter_CD + 2) + 1)
This number is then used to select a packet format which contains at
least this many scaled timestamp bits.
Authors' Addresses
Ghyslain Pelletier
Ericsson
Box 920
Lulea SE-971 28
Sweden
Phone: +46 (0) 8 404 29 43
Email: ghyslain.pelletier@ericsson.com
Kristofer Sandlund
Ericsson
Box 920
Lulea SE-971 28
Sweden
Phone: +46 (0) 8 404 41 58
Email: kristofer.sandlund@ericsson.com
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