One document matched: draft-ietf-xrblock-rtcp-xr-discard-rle-metrics-07.xml
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<rfc ipr="trust200902"
docName="draft-ietf-xrblock-rtcp-xr-discard-rle-metrics-07" category="std">
<!-- What is the category field value-->
<front>
<title abbrev="RTCP XR Discard RLE">
RTP Control Protocol (RTCP) Extended Report (XR) for Run Length Encoding (RLE) of Discarded Packets
</title>
<author initials="J." surname="Ott" fullname="Joerg Ott">
<organization>Aalto University</organization>
<address>
<postal>
<street>School of Electrical Engineering</street>
<street>Otakaari 5 A</street>
<city>Espoo</city>
<region>FIN</region><code>02150</code>
<country>Finland</country>
</postal>
<email>jo@comnet.tkk.fi</email>
</address>
</author>
<author fullname="Varun Singh" initials="V" surname="Singh" role="editor">
<organization>Aalto University</organization>
<address>
<postal>
<street>School of Electrical Engineering</street>
<street>Otakaari 5 A</street>
<city>Espoo</city>
<region>FIN</region>
<code>02150</code>
<country>Finland</country>
</postal>
<email>varun@comnet.tkk.fi</email>
<uri>http://www.netlab.tkk.fi/~varun/</uri>
</address>
</author>
<author initials="I." surname="Curcio" fullname="Igor D.D. Curcio">
<organization>Nokia Research Center</organization>
<address>
<postal>
<street>P.O. Box 1000 (Visiokatu 3)</street>
<city>Tampere</city> <region>FIN</region><code>33721</code>
<country>Finland</country>
</postal>
<email>igor.curcio@nokia.com</email>
</address>
</author>
<date year="2013" />
<area>RAI</area>
<workgroup>XR Block Working Group</workgroup>
<keyword>RTP</keyword>
<keyword>RTCP</keyword>
<keyword>discard metrics</keyword>
<abstract>
<t>
The RTP Control Protocol (RTCP) is used in conjunction with the Real-
time Transport Protocol (RTP) in to provide a variety of short-term and
long-term reception statistics. The available reporting may include
aggregate information across longer periods of time as well as
individual packet reporting. This document specifies a per-packet report
metric capturing individual packets discarded from the de-jitter buffer
after successful reception.
</t>
</abstract>
</front>
<middle>
<section title="Introduction">
<t>
<xref target="RFC3550">RTP</xref> provides a transport for real-time
media flows such as audio and video together with the RTP control
protocol (RTCP) which provides periodic feedback about the media streams
received in a specific duration. In addition, RTCP can be used for
timely feedback about individual events to report (e.g., packet loss)
<xref target="RFC4585"/>. Both long-term and short-term feedback enable
a media sender to adapt its media transmission and/or encoding
dynamically to the observed path characteristics.
</t>
<t>
<xref target="RFC3611">RFC3611</xref> defines RTCP Extended Reports as a
detailed reporting framework to provide more than just the coarse
Receiver Report (RR) statistics. The detailed reporting may enable a
media sender to react more appropriately to the observed networking
conditions as these can be characterized better, although at the expense
of extra overhead.
</t>
<t>
Among many other report blocks, RFC3611 specifies the Loss Run Length
Encoding (RLE) block which reports runs of packets received and lost
with the granularity of individual packets. This can help both error
recovery and path loss characterization. In addition to lost packets,
RFC3611 defines the notion of "discarded" packets: packets that were
received but dropped from the de-jitter buffer because they were either
too early (for buffering) or too late (for playout). The "discard rate"
metric is part of the VoIP metrics report block even though it is not
just applicable to audio: it is specified as the fraction of discarded
packets since the beginning of the session. See section 4.7.1 of <xref
target="RFC3611">RFC3611</xref>. The discard metric is believed to be
applicable to a large class of RTP applications which use a de-jitter
buffer <xref target="RFC5481">RFC5481</xref>.
</t>
<t>
Recently proposed extensions to the Extended Reports (XR) reporting
suggest enhancing this discard metric:
<list style="symbols">
<t>
Reporting the number of discarded packets in a measurement interval,
i.e., during either the last reporting interval or since the beginning
of the session, as indicated by a flag in the suggested XR report <xref
target="I-D.ietf-xrblock-rtcp-xr-discard"/>. If an endpoint needs to
report packet discard due to other reasons than early- and late-arrival
(for example, discard due to duplication, redundancy, etc.) then it
should consider using the Discarded Packets Report Block <xref
target="I-D.ietf-xrblock-rtcp-xr-discard"/>.
</t>
<t>
Reporting gaps and bursts of discarded packets during a measurement
interval, i.e., the last reporting interval or the duration of the
session <xref target="I-D.ietf-xrblock-rtcp-xr-burst-gap-discard"/>.
</t>
<t>
Reporting the sum of payload bytes discarded during a measurement
interval, i.e., the last reporting interval or the duration of the
session
<xref target="I-D.singh-xrblock-rtcp-xr-bytes-discarded-metric"/>.
</t>
</list>
</t>
<t>
However, none of these metrics allow a receiver to report precisely
which packets were discarded. While this information could in theory be
derived from high-frequency reporting on the number of discarded packets
<xref target="I-D.ietf-xrblock-rtcp-xr-discard"/> or from the gap/burst
report <xref target="I-D.ietf-xrblock-rtcp-xr-burst-gap-discard"/>,
these two mechanisms do not appear feasible: The former would require an
unduly high amount of reporting which still might not be sufficient due
to the non-deterministic scheduling of RTCP packets. The latter incur
significant complexity and reporting overhead and might still not
deliver the desired accuracy.
</t>
<t>
This document defines a discard report block following the idea of the
run-length encoding applied for lost and received packets in
<xref target="RFC3611" />.
</t>
<!-- <t>
Alternatively, if the sender keeps a history of the size of the packets reported
in the measurement interval then the sender can calculate the number of
bytes discarded from the information in the discard RLE block.
</t> -->
</section>
<section title="Terminology" anchor="sec-terminology">
<t>
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 BCP 14,
<xref target="RFC2119">RFC 2119</xref>.
</t>
<t>
The terminology defined in <xref target="RFC3550">RTP</xref> and
in the extensions for XR reporting <xref target="RFC3611"/> applies.
</t>
</section>
<section title="XR Discard RLE Report Block" anchor="spec">
<t>
The XR Discard RLE report block uses the same format as specified for the
loss and duplicate report blocks in <xref target="RFC3611" />. <xref
target="packet-format-rle"/> describes the packet format. The fields "BT",
"T", "block length", "SSRC of source", "begin_seq", and "end_seq" have the
same semantics and representation as defined in <xref target="RFC3611" />,
with the addition of the "E" flag to indicate the reason for discard. The
"chunks" encoding the run length have the same representation as in
RFC3611, but encode discarded packets. A definition of a discarded packet
is given in <xref target="I-D.ietf-xrblock-rtcp-xr-discard"/>. </t>
<!--
<t>The XR Discard RLE report block uses exactly the same format, parameter
and chunk definitions as the Loss RLE Report Block defined in RFC3611
Section 4.1 with the sole change that Chunks represent counts of discarded
packets rather than lost packets. A definition of a discarded packet is
given in draft-ietf-xrblock-xr-discard.</t>
-->
<t>
<vspace blankLines="5" />
<figure anchor="packet-format-rle" title="XR Discard RLE Report Block">
<artwork><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BT=DRLE |rsvd |E| T | block length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SSRC of source |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| begin_seq | end_seq |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| chunk 1 | chunk 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: ... :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| chunk n-1 | chunk n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork>
</figure>
</t>
<t>
Block Type (BT, 8 bits): A Run-length encoded Discarded Packets Report
Block is identified by the constant DRLE.
</t>
<t>
[Note to RFC Editor: please replace DRLE with the IANA provided RTCP XR
block type for this block. Please remove this note prior to publication as
an RFC.]
</t>
<t>
rsvd (3 bits): This field is reserved for future definition. In the
absence of such definition, the bits in this field MUST be set to zero and
MUST be ignored by the receiver.
<!-- These reserved bits MUST be set to zero by media receivers and MUST
be ignored by media senders. -->
</t>
<t>
The 'E' bit is introduced to distinguish between packets discarded due
to early arrival and those discarded due to late arrival. The 'E' bit
is set to '1' if the chunks represent packets discarded due to
too early arrival and is set to '0' otherwise.
</t>
<t>
In case both early and late discarded packets shall be reported, two
Discard RLE report blocks MUST be included; their sequence number range
MAY overlap, but individual packets MUST only be reported as either early
or late and not appear marked in both. If packets appear in both report
blocks, the conflicting packets are ignored. Packets reported in neither
are considered to be properly received and not discarded.
</t>
<t>
Discard RLE Report Blocks SHOULD be sent in conjunction with an RTCP RR
as a compound RTCP packet.
</t>
<!-- <t>
Editor's node: is it acceptable to use one of the 'reserved' bits for this
purpose or should two block types be used?
</t> -->
</section>
<section title="Protocol Operation" anchor="protocol">
<t>
This section describes the behavior of the reporting node (= media
receiver) and the media sender.
</t>
<section title="Reporting Node (Receiver)">
<t>
Transmission of RTCP XR Discard RLE Reports is up to the discretion of
the media receiver, as is the reporting granularity. However, it is
RECOMMENDED that the media receiver signals all discarded packets using
the method defined in this document. If all packets over a reporting
period were discarded, the media receiver MAY use the Discard Report
Block <xref target="I-D.ietf-xrblock-rtcp-xr-discard"/> instead. In case
of limited available reporting bandwidth, it is up to the receiver
whether or not to include RTCP XR Discard RLE reports.
</t>
<t>
The media receiver MAY send the Discard RLE Reports as part of the
regularly scheduled RTCP packets as per RFC3550. It MAY also include
Discard RLE Reports in immediate or early feedback packets as per
RFC4585.
</t>
</section>
<section title="Media Sender">
<t>
The media sender MUST be prepared to operate without receiving any
Discard RLE reports. If Discard RLE reports are generated by the
media receiver, the media sender cannot rely on all these reports being
received, nor can the media sender rely on a regular generation
pattern from the media receiver.
</t>
<t>
However, if the media sender receives any RTCP reports but no
Discard RLE report blocks and is aware that the media receiver supports
Discard RLE report blocks, it MAY assume that no packets were discarded
at the media receiver.
</t>
</section>
</section>
<section title="SDP signaling" anchor="sdp">
<!-- <t>
The report blocks specified in this document define extensions to RTCP XR
reporting. Whether or not this specific extended report is sent is left to
the discretion of the receiver. Its presence may enable better operation
of the sender since more detailed information is available. Not providing
this information will make the sender rely on other RTCP reports.
</t> -->
<t>
A participant of a media session MAY use SDP to signal its support for the
report block specified in this document or use them without any prior
signaling (see section 5 of <xref target="RFC3611" />).
</t>
<t>
For signaling in SDP, the RTCP XR attribute as defined in <xref
target="RFC3611" /> MUST be used. The SDP <xref target="RFC4566" />
attribute 'xr-format' defined in RFC3611 is augmented as described in the
following to indicate the the discard RLE metric.
</t>
<t>
<figure>
<artwork><![CDATA[
rtcp-xr-attrib = "a=" "rtcp-xr" ":" [xr-format *(SP xr-format)]
CRLF ; defined in [RFC3611]
xr-format =/ xr-discard-rle
xr-discard-rle = "discard-rle"
]]></artwork>
</figure>
</t>
<t>
The parameter 'discard-rle' is used to indicate support for the
Discard RLE Report Block defined in <xref target="spec"/>.
</t>
<!-- <t>
For signaling support of the RLE discard metric and bytes discarded
metric, the rules defined in RFC3611 apply. Generally, senders and
receivers SHOULD indicate this capability if they support these metrics
and would like to use it in the specific media session being signaled. The
receiver MAY decide not to send discard information unless it knows about
the sender's support to save on RTCP reporting bandwidth.
</t> -->
<t>
When SDP is used in Offer/Answer context, the mechanism defined in <xref
target="RFC3611" /> for unilateral "rtcp-xr" attribute parameters applies
(see section 5.2 of <xref target="RFC3611" />).
</t>
</section>
<section title="Security Considerations" anchor="security">
<t>
The Discard RLE block provides per-packet statistics so the risk to
confidentiality documented in Section 7, paragraph 3 of <xref
target="RFC3611" /> applies. In some situations, returning very detailed
error information (e.g., over-range measurement or measurement
unavailable) using this report block can provide an attacker with insight
into the security processing. Implementers should consider the guidance in
<xref target="I-D.ietf-avt-srtp-not-mandatory" /> for using appropriate
security mechanisms, i.e., where security is a concern, the implementation
should apply encryption and authentication to the report block. For
example this can be achieved by using the AVPF profile together with the
Secure RTP profile as defined in <xref target="RFC3711" />; an appropriate
combination of the two profiles (an "SAVPF") is specified in <xref
target="RFC5124" />. However, other mechanisms also exist (documented in
<xref target="I-D.ietf-avtcore-rtp-security-options" />) and might be more
suitable.
</t>
<t>
Additionally, The security considerations of <xref target="RFC3550" />,
<xref target="RFC3611" />, and <xref target="RFC4585" /> apply.
<!-- Since this document offers only a more precise reporting for an
already existing metric, no further security implications are foreseen.
-->
</t>
</section>
<section title="IANA Considerations" anchor="iana">
<t>
New block types for RTCP XR are subject to IANA registration. For
general guidelines on IANA considerations for RTCP XR, refer to
<xref target="RFC3611" />.
</t>
<section title="XR Report Block Registration">
<t>
This document extends the IANA "RTP Control Protocol Extended Reports
(RTCP XR) Block Type Registry" by a new value: DRLE (Discard RLE
Report).
</t>
<t>
[Note to RFC Editor: please replace DRLE with the IANA provided RTCP XR
block type for this block here and in the diagrams above. Please remove
this note prior to publication as an RFC.]
</t>
</section>
<section title="SDP Parameter Registration">
<t>
This document registers a new parameters for the Session Description
Protocol (SDP), "discard-rle" in the "RTP Control Protocol Extended
Reports (RTCP XR) Session Description Protocol (SDP) Parameters
Registry".
</t>
</section>
<section title="Contact information for IANA registrations">
<t>
Joerg Ott (jo@comnet.tkk.fi)
</t>
<t>
Aalto University Comnet, Otakaari 5A, 02150 Espoo, Finland.
</t>
</section>
</section>
<section title="Acknowledgments">
<t>
The authors would like to thank
Alan Clark,
Roni Even,
Sam Hartman,
Colin Perkins,
Dan Romascanu,
Dan Wing, and
Qin Wu
for providing valuable feedback on earlier versions of this draft.
</t>
</section>
</middle>
<back>
<references title="Normative References">
&rfc2119;
&rfc3550;
&rfc3611;
&rfc4585;
&rfc4566;
&I-D.ietf-xrblock-rtcp-xr-discard;
</references>
<references title="Informative References">
&I-D.ietf-xrblock-rtcp-xr-burst-gap-discard;
&rfc5481;
&rfc3711;
&rfc5124;
&I-D.ietf-avt-srtp-not-mandatory;
&I-D.ietf-avtcore-rtp-security-options;
&I-D.singh-xrblock-rtcp-xr-bytes-discarded-metric;
</references>
<section title="Metrics represented using RFC6390 Template">
<t> RFC EDITOR NOTE: please change XXXX in [RFCXXXX] by the new RFC
number, when assigned. </t>
<t> <list style="letters">
<t> Run-length encoding (RLE) of Discarded Packets Metric
<list style="symbols">
<t> Metric Name: Discard Run-length encoding Metric </t>
<t> Metric Description: Instances of packets discarded over the
period covered by this report. </t>
<t> Method of Measurement or Calculation: See section 3, for the
definition of Discard RLE [RFCXXXX] and section 4.1 of RFC3611 for
Run-length encoding.</t>
<t> Units of Measurement: Every packet in the interval is reported as
discarded or not. See section 3 for the definition of Discard RLE
[RFCXXXX].</t>
<t> Measurement Point(s) with Potential Measurement Domain: The
measurement of these metrics is made at the receiving end of the RTP
stream. </t>
<t> Measurement Timing: Each packet between a beginning sequence
number (begin_seq) and ending sequence number (end_seq) are reported
as discarded or not. See section 3 for the definition of Discard RLE
[RFCXXXX].</t>
<t>Use and applications: See section 1, paragraph 1 of [RFCXXXX].</t>
<t> Reporting model: See RFC3611. </t>
</list> </t>
</list> </t>
</section>
<section anchor="App-a" title="Change Log">
<t>Note to the RFC-Editor: please remove this section prior to
publication as an RFC.</t>
<section title="changes in draft-ietf-xrblock-rtcp-xr-discard-rle-metrics-00">
<t><list style="symbols">
<t>Changed the interval flag from 1 to 2 bits in the discarded
bytes report. Also added the measurement identification
tag to the block.</t>
<t>Added this section.</t>
</list></t>
</section>
<section title="changes in draft-ietf-xrblock-rtcp-xr-discard-rle-metrics-01">
<t><list style="symbols">
<t>Removed the measurement identification tag in the bytes
discarded block.</t>
</list></t>
</section>
<section title="changes in draft-ietf-xrblock-rtcp-xr-discard-rle-metrics-02">
<t><list style="symbols">
<t>Removed the extra Tag bits from the Discarded bytes XR block.</t>
<t>Clarified use of measurement identity block in Section
4 and 5.2</t>
</list></t>
</section>
<section title="changes in draft-ietf-xrblock-rtcp-xr-discard-rle-metrics-03">
<t><list style="symbols">
<t>Added explanation for block length in bytes discarded block.</t>
<t>Added an acknowledgement section.</t>
</list></t>
</section>
<section title="changes in draft-ietf-xrblock-rtcp-xr-discard-rle-metrics-04">
<t><list style="symbols">
<t>Added Block Type definition to each XRBlock.</t>
<t>Made changes requested in WGLC.</t>
</list></t>
</section>
<section title="changes in draft-ietf-xrblock-rtcp-xr-discard-rle-metrics-05">
<t><list style="symbols">
<t>Made changes requested by SDP directorate.</t>
</list></t>
</section>
<section title="changes in draft-ietf-xrblock-rtcp-xr-discard-rle-metrics-06">
<t><list style="symbols">
<t>Editorial fixes based on review from Gen-art and IESG
review.</t>
</list></t>
</section>
<section title="changes in draft-ietf-xrblock-rtcp-xr-discard-rle-metrics-07">
<t><list style="symbols">
<t>Editorial fixes based on review from IESG.</t>
<t>Editorial fixes based on Security and PM directorate.</t>
<t>Split bytes discarded from this draft to another.</t>
<t>Updated Security Considerations Section.</t>
<t>This draft now normatively cites the definition of discards
in 'packets discarded' draft.</t>
</list></t>
</section>
</section>
</back>
</rfc>
<!-- LocalWords: xref CDATA -->
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