One document matched: draft-wing-avt-rtp-noop-00.txt
Internet Engineering Task Force Flemming Andreasen
MMUSIC Working Group David Oran
INTERNET-DRAFT Dan Wing
Expires: August 2004 Cisco Systems
February, 2004
RTP No-Op Payload Format
<draft-wing-avt-rtp-noop-00.txt>
Status of this memo
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Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
This document defines an no-op payload format for the Real-time
Transport Protocol (RTP), and a mechanism to request an immediate
RTCP report. This can be used to verify RTP connectivity and to
keep Network Address Translator (NAT) bindings and Firewall pinholes
open.
INTERNET-DRAFT RTP No-Op Payload February 2004
TABLE OF CONTENTS
1. Introduction.....................................................2
1.1 Notational Conventions............................................2
2. RTP Payload Format for No-Op.......................................3
2.2 Registration......................................................3
2.3 Use of RTP Header Fields..........................................3
2.4 Payload Format....................................................3
2.5 Sender Operation..................................................4
2.6 Mixer, Translator Operation.......................................4
2.7 Receiver Operation................................................4
2.8 Indication of No-OP Capability using SDP..........................5
3. MIME Registration..................................................5
3.1. audio/no-op......................................................5
4. Security Considerations............................................6
5. Acknowledgements...................................................6
6. Authors' Addresses.................................................6
7. Normative References...............................................6
8. Informative References.............................................6
Intellectual Property Statement.......................................7
Full Copyright Statement..............................................7
Acknowledgement.......................................................8
1. Introduction
This memo defines a new RTP payload format called "no-op". This
payload behaves like a normal RTP payload, except that it isn't
played by the receiver.
This new payload format is useful for:
* bearer continuity testing, such as at the beginning of a call;
* keepalives to keep NAT bindings open when RTP media traffic is
not otherwise being transmitted;
For testing the RTP path, an RTP sender may transmit several No-Op
payload packets with the Request Immediate RTCP bit set to 0,
followed by one No-Op payload packet with the Request Immediate RTCP
bit set to 1. This would cause the RTP receiver to send an RTCP
report indicating the quality of the RTP path. The RTP sender could
then decide to continue with call setup, abort the session, or
perform some other action.
1.1 Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "MUST", "MUST NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
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2. RTP Payload Format for No-Op
The no-op payload format is carried as part of the RTP stream, and
MUST use the same sequence number space, SSRC, and timestamp base as
the regular media.
2.2 Registration
The RTP payload format is designated as "no-op" and the MIME type as
"audio/no-op". The default clock rate is 8000 Hz, but other rates
MAY be used. In accordance with current practice, this payload
format does not have a static payload type number, but uses a RTP
payload type number established dynamically and out-of-band.
2.3 Use of RTP Header Fields
Timestamp: The RTP timestamp reflects the measurement point
for the current packet. The receiver calculates
jitter for RTCP receiver reports based on all
packets with a given timestamp. Note: The jitter
value should primarily be used as a means for
comparing the reception quality between two users
or two time-periods, not as an absolute measure.
Marker bit: The RTP marker bit has no special significance for
this payload type.
2.4 Payload Format
The payload format is shown in Figure 1.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R| reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| padding (OPTIONAL) |
| .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The payload contains at least 4 bytes. The first 32 bits are
defined as follows:
bit 0: "R", "Request immediate RTCP", is used to request
transmission of an immediate RTCP report (see section
2.7).
bits 1-31: Reserved, and all bits MUST be 0.
Additional padding bytes MAY be appended up to the negotiated ptime
value in SDP (see section 2.6). These bytes MUST contain all 0
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bits. Padding may be useful to generate RTP packets that are the
same size as another payload (such as a normal voice payload).
2.5 Sender Operation
A source MAY send normal RTP audio and the no-op payload format for
the same time instants (but with different sequence numbers of
course). This might be done in conjunction with this payload
format's "Request Immediate RTCP" opcode.
2.6 Mixer, Translator Operation
An RTP mixer or unicast-to-unicast RTP translator SHOULD forward RTP
No-Op payload packets normally. A unicast-to-multicast RTP
translator SHOULD replicate RTP No-Op payload packets normally.
A multicast-to-unicast RTP translator SHOULD NOT replicate an RTP
No-Op packet with the Request Immediate RTCP bit set, because the
receivers won't be able to prevent flooding of the multicast RTP
sender.
2.7 Receiver Operation
Upon receipt of an RTP packet with the No-Op payload format and the
Send Immediate RTCP Report bit set to 0, the receiver performs
normal RTP receive operations on it -- incrementing the RTP receive
counter, calculating jitter, and so on. The receiver then discards
the packet -- it is not used to play out data.
Upon receipt of an RTP packet with the No-Op payload format and the
Send Immediate RTCP Report bit set to 1, the receiver performs the
steps above and:
* if listening on a multicast IP address, the receiver MUST not
send an immediate RTCP report, and the receiver MUST follow the
normal RTCP transmission rules [RFC3550, sections 6.2 and 6.3].
* if listening on a unicast IP address and sending RTP traffic,
the receiver prepares to send an RTCP sender report, and
* if listening on a unicast IP address and receiving RTP traffic,
the receiver prepares to send an RTCP receiver report.
In all cases, before actually sending its RTCP report, the RTCP
bandwidth limits and randomization interval MUST be observed
[RFC3550, sections 6.2 and 6.3], most especially when multiple SSRCs
are in the same session.
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2.8 Indication of No-OP Capability using SDP
Senders and receivers may indicate support for the No-Op payload
format, for example, by using the Session Description Protocol
([SDP]).
If successful completion of RTP No-Op is required before completing
call establishment -- such as to verify the existence or quality of
the bearer path -- No-Op preconditions can be used [Andreasen].
The default packetization interval for this payload type is 20ms
(ptime:20) but alternate values can be advertised in SDP using the
ptime attribute value [SDP].
3. MIME Registration
3.1. audio/no-op
MIME media type name: audio
MIME subtype name: no-op
Required parameters: none
Optional parameters: none
Encoding considerations: This type is only defined for
transfer via RTP [1].
Security considerations: See the "Security Considerations"
section in this document.
Interoperability considerations: none
Published specification: This document.
Applications which use this media: The "no-op" audio subtype
is used to maintain network state or verify network
connectivity, when a more traditional RTP payload type
cannot be used.
Additional information:
1. Magic number(s): N/A
2. File extension(s): N/A
3. Macintosh file type code: N/A
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4. Security Considerations
Without security of the RTP stream (via SRTP [SRTP], IPsec, or other
means), it is possible for an attacker to spoof RTP packets,
including this new packet type. As this new RTP payload type
includes a method to request immediate transmission of RTCP, this
could be used to cause endpoints to flood the network with RTCP
reports. Thus, the RTCP transmissions MUST NOT exceed the bandwidth
recommendations described in section 6.3 of [RFC3550].
5. Acknowledgements
Thanks to Henning Schulzrinne for suggesting using RTCP as a
feedback mechanism.
6. Authors' Addresses
Flemming Andreasen
Cisco Systems, Inc.
499 Thornall Street, 8th Floor
Edison, NJ 08837 USA
EMail: fandreas@cisco.com
David Oran
Cisco Systems, Inc.
7 Ladyslipper Lane
Acton, MA 01720 USA
EMail: oran@cisco.com
Dan Wing
Cisco Systems, Inc.
170 West Tasman Drive
San Jose, CA 95134 USA
EMail: dwing@cisco.com
7. Normative References
[RFC3550] H. Schulzrinne, S. Casner, R. Frederick, V. Jacobson,
"RTP: A Transport Protocol for Real-Time Applications",
http://www.ietf.org/rfc/rfc3550.txt.
8. Informative References
[Andreasen] F. Andreasen, "No-Op Preconditions", Work In Progress.
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[RFC3407] F. Andreasen, "Session Description Protocol (SDP) Simple
Capability Declaration", October 2002,
http://www.ietf.org/rfc/rfc3407.txt
[SDP] M. Handley and V. Jacobson, "SDP: Session Description
Protocol", April 1998, http://www.ietf.org/rfc/rfc2327.txt.
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