AVT F. Andreasen Internet-Draft D. Oran Intended status: Standards Track D. Wing Expires: August 27, 2007 Cisco Systems, Inc. February 23, 2007 A No-Op Payload Format for RTP draft-ietf-avt-rtp-no-op-01 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on August 27, 2007. Copyright Notice Copyright (C) The IETF Trust (2007). Abstract This document defines an no-op payload format for the Real-time Transport Protocol (RTP). This packet is not played out by receivers. It can be useful as a way to keep Network Address Translator (NAT) bindings and Firewall pinholes open. Other uses are discussed in the document. Andreasen, et al. Expires August 27, 2007 [Page 1] Internet-Draft RTP No-Op Payload Format February 2007 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions Used in this Document . . . . . . . . . . . . . . 4 3. RTP Payload Format for No-Op . . . . . . . . . . . . . . . . . 4 3.1. Registration . . . . . . . . . . . . . . . . . . . . . . . 4 3.2. Use of RTP Header Fields . . . . . . . . . . . . . . . . . 4 3.3. Payload Format . . . . . . . . . . . . . . . . . . . . . . 4 3.4. Sender Operation . . . . . . . . . . . . . . . . . . . . . 5 3.5. Mixer, Translator Operation . . . . . . . . . . . . . . . 5 3.6. Receiver Operation . . . . . . . . . . . . . . . . . . . . 5 3.7. Indication of No-OP Capability using SDP . . . . . . . . . 5 4. Example SDP Offer/Answer . . . . . . . . . . . . . . . . . . . 6 5. MIME Registration . . . . . . . . . . . . . . . . . . . . . . 6 5.1. audio/no-op . . . . . . . . . . . . . . . . . . . . . . . 6 5.2. video/no-op . . . . . . . . . . . . . . . . . . . . . . . 7 5.3. text/no-op . . . . . . . . . . . . . . . . . . . . . . . . 8 6. Security Considerations . . . . . . . . . . . . . . . . . . . 8 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 9.1. Normative References . . . . . . . . . . . . . . . . . . . 9 9.2. Informational References . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9 Intellectual Property and Copyright Statements . . . . . . . . . . 11 Andreasen, et al. Expires August 27, 2007 [Page 2] Internet-Draft RTP No-Op Payload Format February 2007 1. Introduction This memo defines a new RTP payload format called "no-op". This payload behaves like a normal RTP payload, except the RTP packet is not used to play out media. This new payload format is useful for: o facilitating media session reception quality assessment, such as at the beginning of a session; o keepalives to keep NAT bindings and/or firewall pinholes open when RTP media traffic is not otherwise being transmitted. o measurement-based admission control by probing available bandwidth, and o synthetic load generation for performance testing and other minimally-intrusive instrumentation. When an endpoint has a media stream marked as 'recvonly' or 'inactive' the endpoint is not supposed to send any media (i.e., RTP packets). However, to keep a NAT binding alive, the endpoint will need to periodically send packets over the RTP and RTCP ports. RTP No-Op is ideally suited to this. In comparison, if one participant in an audio multicast conference has a 'recvonly' or 'inactive' media stream yet occasionally sends comfort noise packets in order to keep its NAT binding open, these comfort noise packets are interpreted as audio packets by receivers and mixers which can cause undesirable behavior -- such as selection of the primary speaker or the playout of comfort noise when no audio should be played. Unlike Comfort noise [RFC3389], which is specific to voice RTP streams, RTP No-Op is applicable to any kind of RTP stream including video, audio, realtime text, or any other media types that would benefit from the capabilities listed above. This gives RTP No-Op an advantage as a NAT keepalive mechanism. Certain functions and RTP payload types can use RTP No-Op without re-inventing their own payload-specific NAT keepalive mechanism -- such as video muting, Clearmode [RFC4040], and text [RFC4103]. Some audio codecs have their own 'silence' packets. However, some codecs only send such silence packets if the noise floor changes; G.729b [G729B] is an example of such a codec. RTP No-Op allows the RTP stack itself, rather than the codec, to send periodic packets as a keepalive mechanism. Andreasen, et al. Expires August 27, 2007 [Page 3] Internet-Draft RTP No-Op Payload Format February 2007 2. Conventions Used in this Document 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 [RFC2119]. 3. RTP Payload Format for No-Op 3.1. Registration The RTP payload format is designated as "no-op" and the MIME types are "audio/no-op", "video/no-op", and "text/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 out-of-band, e.g. through SDP [RFC4566]. 3.2. Use of RTP Header Fields Timestamp: The RTP timestamp reflects the measurement point for the current packet. The receiver uses this timestamp to calculate jitter for RTCP sender and receiver reports per normal RTP procedures. 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. 3.3. Payload Format The payload format is shown below. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | padding (OPTIONAL) | | .... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: Payload Format The payload contains at least 4 bytes, the first 32 bits are reserved for future use. These bits SHOULD be set to 0. Receivers MUST ignore the value of these bits. Andreasen, et al. Expires August 27, 2007 [Page 4] Internet-Draft RTP No-Op Payload Format February 2007 Additional padding bytes MAY be appended up to the ptime or maxptime value in SDP (see Section 3.7). These bytes MUST be ignored. Padding may be useful to generate RTP packets that are the same size as a normal media payload. 3.4. Sender Operation As discussed in the introduction, endpoints must occasionally send a packet to their RTP and RTCP peer to keep NAT and firewall bindings active, even if the media stream is marked 'recvonly' or 'inactive'. No matter if the media stream is marked 'recvonly', 'sendrecv', 'sendonly', or 'inactive', if approximately 20 seconds elapse with no packets transmitted from the RTP port (either RTP packets or non-RTP packets (e.g., STUN [I-D.ietf-behave-rfc3489bis] packets), then an RTP No-Op packet SHOULD be sent. 3.5. Mixer, Translator Operation An RTP mixer or unicast-to-unicast RTP translator SHOULD forward RTP No-Op payload packets normally; if the input stream is made up of RTP No-Op packets only, a corresponding RTP No-Op packet SHOULD be generated. If the input stream consists of other packets than No-Op, then the No-Op packets SHOULD simply be discarded. A unicast-to- multicast RTP translator SHOULD replicate RTP No-Op payload packets normally. 3.6. Receiver Operation Upon receipt of an RTP packet with the No-Op payload format 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 media. 3.7. 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 [RFC4566]. The default packetization interval for this payload type is 20ms but alternate values can be advertised in SDP using the ptime or maxptime attributes [RFC4566]. Andreasen, et al. Expires August 27, 2007 [Page 5] Internet-Draft RTP No-Op Payload Format February 2007 4. Example SDP Offer/Answer Offer: v=0 o=alice 2890844526 2890844526 IN IP4 host.atlanta.example.com s=- c=IN IP4 host.atlanta.example.com t=0 0 m=audio 49170 RTP/AVP 0 96 a=rtpmap:0 PCMU/8000 a=rtpmap:96 no-op/8000 m=video 41372 RTP/AVP 31 96 a=rtpmap:31 H261/90000 a=rtpmap:96 no-op/90000 Answer: v=0 o=bob 2808844564 2808844564 IN IP4 host.biloxi.example.com s=- c=IN IP4 host.biloxi.example.com t=0 0 m=audio 59174 RTP/AVP 0 96 a=rtpmap:0 PCMU/8000 a=rtpmap:96 no-op/8000 m=video 59170 RTP/AVP 32 96 a=rtpmap:31 H261/90000 a=rtpmap:96 no-op/90000 5. MIME Registration This section registers MIME types for audio/no-op, video/no-op, and text/no-op. 5.1. audio/no-op MIME media type name: audio MIME subtype name: no-op Required parameters: none Optional parameters: none Encoding considerations: none Andreasen, et al. Expires August 27, 2007 [Page 6] Internet-Draft RTP No-Op Payload Format February 2007 Security considerations: See Section 6, "Security Considerations", in this document. Interoperability considerations: none Published specification: This document. Applications which use this media: The "no-op" application 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 5.2. video/no-op MIME media type name: video MIME subtype name: no-op Required parameters: none Optional parameters: none Encoding considerations: none Security considerations: See Section 6, "Security Considerations", in this document. Interoperability considerations: none Published specification: This document. Applications which use this media: The "no-op" application 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 Andreasen, et al. Expires August 27, 2007 [Page 7] Internet-Draft RTP No-Op Payload Format February 2007 3. Macintosh file type code: N/A 5.3. text/no-op MIME media type name: text MIME subtype name: no-op Required parameters: none Optional parameters: none Encoding considerations: none Security considerations: See Section 6, "Security Considerations", in this document. Interoperability considerations: none Published specification: This document. Applications which use this media: The "no-op" application 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 6. Security Considerations There are no additional security considerations for this new RTP payload format; the RTP security considerations from RTP [RFC3550] apply. 7. IANA Considerations IANA is requested to make MIME type registrations as specified above in Section 5 8. Acknowledgments Andreasen, et al. Expires August 27, 2007 [Page 8] Internet-Draft RTP No-Op Payload Format February 2007 9. References 9.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", STD 64, RFC 3550, July 2003. [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session Description Protocol", RFC 4566, July 2006. 9.2. Informational References [I-D.ietf-behave-rfc3489bis] Rosenberg, J., "Simple Traversal Underneath Network Address Translators (NAT) (STUN)", draft-ietf-behave-rfc3489bis-05 (work in progress), October 2006. [RFC3389] Zopf, R., "Real-time Transport Protocol (RTP) Payload for Comfort Noise (CN)", RFC 3389, September 2002. [RFC4040] Kreuter, R., "RTP Payload Format for a 64 kbit/s Transparent Call", RFC 4040, April 2005. [RFC4103] Hellstrom, G. and P. Jones, "RTP Payload for Text Conversation", RFC 4103, June 2005. [G729B] International Telecommunications Union, "G.729 Annex B", November 1999, . Authors' Addresses Flemming Andreasen Cisco Systems, Inc. 499 Thornall Street, 8th Floor Edison, NJ 08837 USA Email: fandreas@cisco.com Andreasen, et al. Expires August 27, 2007 [Page 9] Internet-Draft RTP No-Op Payload Format February 2007 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 Andreasen, et al. Expires August 27, 2007 [Page 10] Internet-Draft RTP No-Op Payload Format February 2007 Full Copyright Statement Copyright (C) The IETF Trust (2007). 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The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Andreasen, et al. Expires August 27, 2007 [Page 11]