Network Working Group H. Desineni Internet-Draft N. Leung Intended status: Standards Track Qualcomm Expires: August 27, 2007 February 23, 2007 'MSR' Bandwidth modifier in SDP Offer/Answer model draft-hdesinen-mmusic-oa-send-bw-attr-02.txt 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). Desineni & Leung Expires August 27, 2007 [Page 1] Internet-Draft Send Bandwidth Modifier in SDP OA February 2007 Abstract This document defines a new SDP bandwidth modifier that can be used to specify the maximum media bitrate in 'send' direction of a stream in SDP offer/answer model. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Background . . . . . . . . . . . . . . . . . . . . . . . . . . 5 4. Use case . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5. The MSR Bandwidth Modifier . . . . . . . . . . . . . . . . . . 7 5.1. Definition . . . . . . . . . . . . . . . . . . . . . . . . 7 5.2. Usage Rules . . . . . . . . . . . . . . . . . . . . . . . 7 5.3. ABNF Definition . . . . . . . . . . . . . . . . . . . . . 7 6. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 7. Security Considerations . . . . . . . . . . . . . . . . . . . 9 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 9.1. Normative References . . . . . . . . . . . . . . . . . . . 11 9.2. Informative References . . . . . . . . . . . . . . . . . . 11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12 Intellectual Property and Copyright Statements . . . . . . . . . . 13 Desineni & Leung Expires August 27, 2007 [Page 2] Internet-Draft Send Bandwidth Modifier in SDP OA February 2007 1. Introduction RFC 3264 defines the SDP Offer/answer model for unicast multimedia sessions where information from both participants is needed for the complete view of the session. According to RFC 3264, bandwidth attribute present in the SDP offer signals the desired bandwidth that the offerer would like to receive. Hence, bandwidth attributes "AS" and "TIAS" defined in RFC 3550 and RFC 3890 respectively can only be used as receive-only attributes in SDP offer/answer model. A stream receiver (Offerer or Answerer) signals the value of "TIAS" based on maximum media bitrate it desires to receive. The stream sender (Answerer or Offerer) may send media at a maximum bitrate much lower than "TIAS". Knowing the sender's (smaller) maximum media bitrate enables better resource allocation. Desineni & Leung Expires August 27, 2007 [Page 3] Internet-Draft Send Bandwidth Modifier in SDP OA February 2007 2. Conventions 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 [1]. Desineni & Leung Expires August 27, 2007 [Page 4] Internet-Draft Send Bandwidth Modifier in SDP OA February 2007 3. Background Section 5.8 of RFC 4566 defines the syntax for "b=" bandwidth attribute. It also defines the bandwidth type "AS" as application's concept of maximum bandwidth. According to section 6.2 of RFC 3550, for RTP based applications, "AS" includes the header overhead due to lower layer transport and network protocols (e.g., UDP, IP ) and does not include the overhead due to link level headers. Section 6.2 of RFC 3890 defines the bandwidth type "TIAS". In the context of RTP transport, "TIAS" provides the bandwidth for RTP payload which includes payload format header and payload data. "TIAS" does not include any other layer overhead including RTP layer. According to RFC3264, any bandwidth attribute present in an SDP offer signals the desired bandwidth that the offerer would like to receive. Hence, bandwidth attributes "AS" and "TIAS" defined in RFC 3550 and RFC 3890 respectively can only be used as receive-only attributes in SDP offer/answer model. Desineni & Leung Expires August 27, 2007 [Page 5] Internet-Draft Send Bandwidth Modifier in SDP OA February 2007 4. Use case In SDP offer/answer model, the answerer's send bitrate for the stream in answerer->offerer direction depends on the value of "AS" or "TIAS" signaled in the SDP offer. The answerer may send media at a bit-rate much lower than "AS" or "TIAS" signaled by the offerer. This could be due to several reasons including QoS resource limitation over the answerer's first hop link. Similarly, offerer's send bitrate for the stream in offerer->answerer direction may be much lower than "AS" or "TIAS" signaled in the SDP answer. Cellular links commonly have some type of QoS negotiation enabling the cellular device to learn the maximum bitrate available over the first hop link. Signaling the maximum media send bitrate to the receiving device can be beneficial to allocate proper QoS resources over the last hop link. This is especially beneficial in preventing resource overallocation when the last hop is a cellular link. Bandwidth inequality over first and last hop links can also arise when the offerer and answerer are attached to different types of networks. E.g., Offerer is a cellular device and answerer is a PC phone with wireline connection. The 'MSR' bandwidth modifier defined in the following section can be used to specify the maximum media bitrate in 'send' direction of a stream. For an example usage, see Section 6. Desineni & Leung Expires August 27, 2007 [Page 6] Internet-Draft Send Bandwidth Modifier in SDP OA February 2007 5. The MSR Bandwidth Modifier 5.1. Definition MSR bandwidth modifier is defined as shown below: b=MSR: ; see [7] for ABNF definition. The Maximum Send Rate (MSR) bandwidth modifier specifies the maximum media bitrate in 'send' direction of a stream in SDP offer/answer model. 'MSR' has an integer bit-rate value in bits per second. A fractional bandwidth value SHALL always be rounded up to the next integer. The bandwidth value is the maximum bit-rate without counting the protocol header bytes from IP or other transport layers like TCP,UDP and RTP. 5.2. Usage Rules 'MSR' bandwidth modifier is intended to be used only at the SDP media level. It MUST not be used with a 'recvonly' stream. 5.3. ABNF Definition The bandwidth modifier: MSR-bandwidth-def = "b" "=" "MSR" ":" bandwidth-value CRLF bandwidth-value = 1*DIGIT Desineni & Leung Expires August 27, 2007 [Page 7] Internet-Draft Send Bandwidth Modifier in SDP OA February 2007 6. Example Alice offers a receive only stream to Bob with maximum receive media bitrate ("TIAS") 128000bps (H.263 profile 0 level 45). Bob responds with SDP answer by marking the stream as sendonly. Note that the SDP answer from Bob does not include any bandwidth attribute as it contains a sendonly stream. [Offer from Alice] m=video 34564 RTP/AVP 96 a=rtpmap:96 h263-1998/90000 a=fmtp:96 profile=0; level=45; b=TIAS:128000 a=maxprate:20 a=recvonly [Answer from Bob] m=video 46236 RTP/AVP 96 a=rtpmap:96 h263-1998/90000 a=fmtp:96 profile=0;level=45; a=sendonly Due to QoS limitation on its first hop link, Bob can send media at maximum bitrate of 64000bps only. Unaware of Bob's maximum media bitrate, Alice overallocates QoS resources on its access (last hop) link. Signaling Bob's maximum media bitrate in the SDP answer can help Alice reserve correct QoS resources in its access (last hop) link. The complete offer/answer example with proposed bandwidth attribute 'MSR' is shown below. [Offer from Alice] m=video 34564 RTP/AVP 96 a=rtpmap:96 h263-1998/90000 a=fmtp:96 profile=0; level=45; b=TIAS:128000 a=maxprate:20 a=recvonly [Answer from Bob] m=video 46236 RTP/AVP 96 a=rtpmap:96 h263-1998/90000 a=fmtp:96 profile=0;level=45; b=MSR:64000 a=sendonly Desineni & Leung Expires August 27, 2007 [Page 8] Internet-Draft Send Bandwidth Modifier in SDP OA February 2007 7. Security Considerations [TBD] Desineni & Leung Expires August 27, 2007 [Page 9] Internet-Draft Send Bandwidth Modifier in SDP OA February 2007 8. IANA Considerations [TBD] Desineni & Leung Expires August 27, 2007 [Page 10] Internet-Draft Send Bandwidth Modifier in SDP OA February 2007 9. References 9.1. Normative References [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [2] Schulzrinne, H., "RTP: A Transport Protocol for Real-Time Applications", STD 64, RFC 3550, March 1997. [3] Rosenberg, J., "An Offer/Answer Model with Session Description Protocol (SDP)", RFC 3264, June 2002. [4] Narten, T., "Guidelines for Writing an IANA Considerations Section in RFCs", RFC 2434, October 1998. [5] Handley, M., "SDP: Session Description Protocol", RFC 4566, July 2006. [6] Westerlund, M., "A Transport Independent Bandwidth Modifier for the Session Description Protocol (SDP)", RFC 3890, September 2004. [7] Crocker, C., "Augmented BNF for Syntax Specifications: ABNF", RFC 2234, November 1997. 9.2. Informative References [8] Schulzrinne, H., "RTP Profile for Audio and Video Conferences with Minimal Control", STD 65, RFC 3551, July 2003. [9] Schulzrinne, H., "Real Time Streaming Protocol (RTSP)", RFC 2326, April 1998. [10] Johnston, A., "SDP Offer/Answer Examples", RFC 4317, December 2005. [11] Westerlund, M., "How to Write an RTP Payload Format", draft-ietf-avt-rtp-howto-00.txt(Work in Progress) , May 2006. Desineni & Leung Expires August 27, 2007 [Page 11] Internet-Draft Send Bandwidth Modifier in SDP OA February 2007 Authors' Addresses Harikishan Desineni Qualcomm 5775 Morehouse Drive San Diego, CA 92126 USA Phone: +1 858 845 8996 Email: hd@qualcomm.com URI: http://www.qualcomm.com Nikolai Leung Qualcomm 7710 Takoma Ave Takoma Park, MD 20912 USA Phone: +1 858 845 3333 Email: nleung@qualcomm.com URI: http://www.qualcomm.com Desineni & Leung Expires August 27, 2007 [Page 12] Internet-Draft Send Bandwidth Modifier in SDP OA February 2007 Full Copyright Statement Copyright (C) The IETF Trust (2007). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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