MMUSIC WG Kylin Wei Internet-Draft Huawei Technologies Expires: December 12, 2006 June 12, 2006 Bitrate header in RTSP draft-wei-mmusic-rtsp-bitrate-header-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 November 20, 2006. Copyright Notice Copyright (C) The Internet Society (2006). Abstract This document presents an integrated solution for multiple bitrates by defining the Bitrate header in RTSP. A client can inquire bitrate range of media source after a successful SETUP request by sending a GET_PARAMETER request with the bitrate parameter to the RTSP server, and then server responds with bitrate range parameter of media source. According to bitrate range parameter value, the client MAY apply for bandwidth reservation by RSVP (Resource Reservation Protocol) [5] or apply for increasing access bandwidth. The client MAY select a suitable bitrate to start with or change transport bitrate during the playing by sending a PLAY request with the Bitrate header. Kylin Wei Expires: December 12, 2006 [Page 1] Internet-Draft Bitrate header in RTSP June 12, 2006 Table of Contents 1. Introduction...................................................3 2. Terminology....................................................4 3. "Bitrate" header and "bitrate" parameter definitions...........5 4. The difference between "a=alt" and "Bitrate" in media description..........................5 5. Use Cases......................................................7 5.1. Inquire bitrate range......................................7 5.2. Changing transport bitrate.................................8 5.2.1. Single media file......................................8 5.2.2. Multiple media files...................................9 6. Security Considerations.......................................10 7. IANA Considerations...........................................11 8. Acknowledges..................................................12 9. References....................................................10 9.1. Normative References......................................13 9.2. Informative References....................................13 Author's Address..................................................14 Intellectual Property and Copyright Statements....................15 Kylin Wei Expires: December 12, 2006 [Page 2] Internet-Draft Bitrate header in RTSP June 12, 2006   1. Introduction There are two obvious problems in QOS (Quality of Service) of video on-demand now. First, the network condition of the internet isn't reliable because the bandwidth and the load of internet often change acutely. But the transport bitrate of media source is constant. So it will affect the quality of video on-demand such as delay and jitter. Second, the actual access bandwidths of many subscribers who order the same media program are different. Such as the access bandwidths of some subscribers are tens of Mbps, and others may be hundreds of Kbps. But media source only has one bitrate, so some users with high access bandwidth can't get better video quality and some users with very low access bandwidth have not enough bandwidth to watch video. So it's necessary that media source can provide more than one bitrate to adapt to complex network condition. Media source has two methods to provide multiple bitrates. First, the simplest way is that media server prepares several media files for the same media program. The bitrates of these files are different from each other. The server could redirect a client to a corresponding media file (URI) according to the client's selection on the bitrate. Second, some scalable coding and multi-rate coding technologies are presented. By using these two kinds of technologies, one media file can provide multiple bitrates. As technology progresses, future advanced video codec can provide a large number of bitrates within one media file. RTSP should provide a way that a client can inquire bitrate range of media source and the client can change transport bitrate at any time. This specification defines the Bitrate header to solve this problem. If a client wants to inquire the bitrate range of media source, it SHOULD send a GET_PARAMETER request with the bitrate parameter after a success SETUP request unless the client does not plan to adjust transport bitrate. When RTSP server receives this request, it will respond bitrate range values in the bitrate parameter field. Kylin Wei Expires: December 12, 2006 [Page 3] Internet-Draft Bitrate header in RTSP June 12, 2006 After the client got the bitrate parameter value, it can take action according to the bitrate parameter value. For example, bitrate parameter is "512K, 1M, 2M", but access bandwidth of a subscriber is 0.5Mbps, the subscriber could temporarily apply for more access bandwidth in the service gateway from 0.5Mbps to 1Mbps or 2Mbps, and original access bandwidth would be restored after two hours. This action may be common use in the community video on-demand and IPTV. If video on-demand occurs on the internet, to get a steady network bandwidth, a subscriber can apply for bandwidth reservation by RSVP. For instance, the bitrate parameter is "1M, 2M, 3M", and the subscriber can apply for reserving 2Mbps bandwidth to specified media stream. A user may also directly select a suitable bitrate to start with according to his evaluation of current network condition and access bandwidth. For instance, the user may select 2Mbps bitrate because subscriber access bandwidth is 2.5Mbps. Other important use case is that a user can change transport bitrate during the play. For example, a user has played a movie for ten minutes, and he felt that the video starts to show slowly. He thought that congestion may occur in current network, so he selected a lower bitrate on his own initiative. Such as bitrate parameter is "1M, 2M, 3M", he changed transport bitrate from 2Mbps to 1Mbps. 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 [1]. Kylin Wei Expires: December 12, 2006 [Page 4] Internet-Draft Bitrate header in RTSP June 12, 2006 3. "Bitrate" header and "bitrate" parameter definitions The bitrate parameter is used by a client to inquire bitrate range of media source. A GET_PARAMETER request with the bitrate parameter indicates that a client want to inquire bitrate range of media source. The Bitrate header is used to change transport bitrate. A PLAY request with the Bitrate header indicates that a client want to change transport bitrate. Bitrate header filed value MUST be one value of bitrate range of media source. The bitrate parameter may be several separate values such as "512K, 1M, 2M", and may also be a continuous range value such as "512K-2.5M". Syntax: HCOLON, CRLF, COMMA and DIGIT are defined in rfc2326bis [2]. Bitrate header: Bitrate = "Bitrate" HCOLON bitrate-value CRLF bitrate parameter: bitrate = "bitrate" HCOLON bitrate-sep / bitrate-con CRLF bitrate-sep = bitrate-value *(COMMA bitrate-value) bitrate-con = bitrate-value "-" bitrate-value bitrate-value = (1*DIGIT "K") / (1*DIGIT [ "." 1*DIGIT] "M") 4. The difference between "a=alt" and "Bitrate" in media description "a=alt" attribute had been defined in 3GPP TS 26.234 [6] used to present some alternative bitrates and then client can use the URI to indicate which alternative bitrate it wishes to start with. Sometimes it will result in a large SDP body [4]. For example, advanced video codec which can provide a large number of bitrates within one media file will be presented. If a media file can present hundreds or thousands of bitrates, by using "a=alt" attribute, server must offer all these alternative bitrates and their private description to the client. Then SDP which the client wishes to receive will become very large and redundant. A better plan is that the server should only offer the default alternative bitrate within one media description in the DESCRIBE Kylin Wei Expires: December 12, 2006 [Page 5] Internet-Draft Bitrate header in RTSP June 12, 2006 response. The private description of other alternatives will be offered when only this alternative is going to be used. A client SHOULD inquire bitrate range after a successful SETUP request. The server then respond with bitrate parameter value of the media file. If the client wants to change transport bitrate, it will send a PLAY request with Bitrate header field. Server then changes transport bitrate as the client wanted and then appends necessary description of this bitrate into the PLAY response. Follow example is a simple contrast. Unnecessary details are omitted for clarity in this example. Using "a=alt" attribute v=0 o=ericsson_user 1 1 IN IP4 130.240.188.69 s=A basic video presentation c=IN IP4 0.0.0.0 b=AS:44 a=control:* a=alt-group:BW:AS:16="3",44="4",104="5" a=range:npt=0-150.2 t=0 0 m=video 0 RTP/AVP 98 b=AS:44 a=rtpmap:98 MP4V-ES/90000 a=control:trackID=4 a=fmtp:98 profile-level-id=8; config=01010000012000884006682C2090A21F a=range:npt=0-150.2 a=X-initpredecbufperiod:98000 a=alt-default-id:4 a=alt:3:b=AS:16 a=alt:3:a=control:trackID=3 a=alt:3:a=X-initpredecbufperiod:48000 a=alt:5:b=AS:104 a=alt:5:a=control:trackID=5 a=alt:5:a=X-initpredecbufperiod:150000 Using Bitrate header v=0 o=ericsson_user 1 1 IN IP4 130.240.188.69 s=A basic video presentation c=IN IP4 0.0.0.0 b=AS:44 Kylin Wei Expires: December 12, 2006 [Page 6] Internet-Draft Bitrate header in RTSP June 12, 2006 a=control:* a=range:npt=0-150.2 t=0 0 m=video 0 RTP/AVP 98 b=AS:44 a=rtpmap:98 MP4V-ES/90000 a=control:trackID=4 a=fmtp:98 profile-level-id=8; config=01010000012000884006682C2090A21F a=range:npt=0-150.2 a=X-initpredecbufperiod:98000 C->S SETUP rtsp://media.example.com/examples/3G_systems.3gp /trackid=4 S->C 200 OK C->S GET_PARAMATER rtsp://media.example.com/examples/3G_systems.3gp/ trackid=4 bitrate S->C 200 OK bitrate: 44K, 16K, 104K C->S PLAY rtsp://media.example.com/examples/3G_systems.3gp/trackid=4 Bitrate: 104K S->C 200 OK Bitrate: 104K x-initpredecbufperiod: 150000 5. Use Cases 5.1. Inquire bitrate range After a successful SETUP request, a client SHOULD send a GET_PARAMATER request with the bitrate parameter to inquire bitrate range of media source unless the client does not plan to adjust transport bitrate. If RTSP server doesn't support the bitrate parameter, it MUST respond error 451(Parameter Not Understood) or other error code. Otherwise it MUST respond 200 OK followed by the bitrate parameter value. Example: C->S: GET_PARAMETER rtsp://example.com/movie/ring.avi RTSP/2.0 CSeq: 210 Kylin Wei Expires: December 12, 2006 [Page 7] Internet-Draft Bitrate header in RTSP June 12, 2006 Content-Type: text/parameters Session: mymovie Content-Length: 9 bitrate S->C: RTSP/2.0 200 OK CSeq: 210 Session: mymovie Content-Length: 27 Content-Type: text/parameters bitrate: 512K, 1M, 2M, 3M After the client got the bitrate parameter value, it MUST record these values and show these values to the user. 5.2. Changing transport bitrate After getting the bitrate parameter value, a user can change transport bitrate at any time. The process of changing transport bitrate of single media file is different from that of multiple media files. The Range header is RECOMMENDED to indicate time range of playing program with modified transport bitrate. If a movie has been played for a long time before changing transport bitrate, the client SHOULD start playing from current time point with modified transport bitrate. 5.2.1. Single media file This kind of media file should be encoded by multi-rate coding technology so that it has multiple bitrates. When RTSP server received a client's PLAY request with the Bitrate header, it SHOULD change transport bitrate according to the Bitrate header values. If RTSP server doesn't support the Bitrate header, it MUST respond error 456(Header Field Not Valid) or other error code. If the request of changing transport bitrate can be implemented by server, the private description of new transport bitrate SHOULD be appended into the PLAY response to report to the client unless there isn't necessary private description. The following example will replay from the tenth second by 512Kbps bitrate: Kylin Wei Expires: December 12, 2006 [Page 8] Internet-Draft Bitrate header in RTSP June 12, 2006 C->S: PLAY rtsp://example.com/movie/ring.avi RTSP/2.0 CSeq: 20 User-Agent: PhonyClient/1.2 Bitrate: 512K Range: npt=10- Session: mymovie S->C: RTSP/2.0 200 OK CSeq: 20 Server: PhonyServer/1.0 Date: 2 Feb 2006 18:00:00 GMT Session: mymovie Bitrate: 512K Range: npt=0-5400 RTP-Info: url="rtsp://example.com/movie/ring.avi" ssrc=0E756890:seq=7892;rtptime=78905432 5.2.2. Multiple media files Sometimes there are multiple media files of the same program. They have the same content but their bitrates are different. Such as there are four media files (ring_1.avi, ring_2.avi, ring_3.avi, ring_4.avi) for movie "Ring". Their bitrates are 4Mbps, 2Mbps, 1Mbps and 512Kbps. To avoid a large SDP body, we SHOULD only offer the default media file to a client such as ring_2.avi (2Mbps). RTSP server MUST understand all these information in advance. When a client requests changing transport bitrate, RTSP server responds 200 OK and then redirects the client to a corresponding URI. Example: C->S: PLAY rtsp://example.com/movie/ring_2.avi RTSP/2.0 CSeq: 200 User-Agent: PhonyClient/1.2 Bitrate: 512K Range: npt=10- Session: mymovie S->C: RTSP/2.0 200 OK CSeq: 200 Server: PhonyServer/1.0 Date: 2 Feb 2007 18:00:00 GMT Kylin Wei Expires: December 12, 2006 [Page 9] Internet-Draft Bitrate header in RTSP June 12, 2006 Session: mymovie Bitrate: 512K Range: npt=0-5400 RTP-Info: url="rtsp://example.com/movie/ring_2.avi" ssrc=0E756890:seq=7892;rtptime=78905432 S->C: REDIRECT rtsp://example.com/movie/ring_2.avi RTSP/2.0 CSeq: 201 Location: rtsp://example.com/movie/ring_4.avi Range: npt=10- ;time=20060509T103205Z Session: mymovie C->S: RTSP/2.0 200 OK CSeq: 201 6. Security Considerations The same security considerations apply as for the base RTSP specification, as described in [3]. Kylin Wei Expires: December 12, 2006 [Page 10] Internet-Draft Bitrate header in RTSP June 12, 2006 7. IANA Considerations It is request of IANA to register the "Bitrate" header in the RTSP 1.0 registry at: http://www.iana.org/assignments/rtsp-parameters. Contact name: kylin Wei (weiqikun@huawei.com). Header Name: Bitrate Purpose: See Section 3 Methods: PLAY Request and Response Reference: Section 3 Values: See Reference Kylin Wei Expires: December 12, 2006 [Page 11] Internet-Draft Bitrate header in RTSP June 12, 2006 8. Acknowledges Thanks Spencer Dawkins for providing his valuable advices for this document. Thanks for the discussions from Jaehwan Kim, Colin Perkins and Magnus Westerlund. Thanks Philippe Gentric for providing his draft about stream-switching. Kylin Wei Expires: December 12, 2006 [Page 12] Internet-Draft Bitrate header in RTSP June 12, 2006 9. References 9.1. Normative References [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", RFC 2119, March 1997. [2] H. Schulzrinne, A. Rao, R. Lanphier, Magnus Westerlund, A. Narasimhan, "Real Time Streaming Protocol 2.0 (RTSP)", draft-ietf-mmusic-rfc2326bis-12, March 2006. [3] H. Schulzrinne, A. Rao, R. Lanphier, "Real Time Streaming Protocol (RTSP)", RFC 2326, April 1998. [4] M. Handley, V. Jacobson, "SDP: Session Description Protocol", RFC 2327, April 1998. 9.2. Informative References [5] Braden, R., Zhang, L., Berson, S., Herzog, S. and S. Jamin, "Resource ReSerVation protocol (RSVP) -- Version 1 Functional Specification", RFC 2205, September 1997. [6] 3GPP TS 26.234 "Transparent end-to-end Packet-switched Streaming Service (PSS); Protocols and codecs" (Release 6) version 6.7.0 (2006-03), 3rd Generation Partnership Project (3GPP) Kylin Wei Expires: December 12, 2006 [Page 13] Internet-Draft Bitrate header in RTSP June 12, 2006 Author's Address Kylin Wei Huawei Technologies NanJing Institute,Huawei Technologies Co.,Ltd. Floor 10, HuiHong Mansion, No.91 BaiXia Rd. NanJing, P.R. of China Phone: +86 25 8456 5404 Email: weiqikun@huawei.com URI: www.huawei.com Kylin Wei Expires: December 12, 2006 [Page 14] Internet-Draft Bitrate header in RTSP June 12, 2006 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. 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Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Copyright Statement Copyright (C) The Internet Society (2006). 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. Acknowledgment Funding for the RFC Editor function is currently provided by the Internet Society. Kylin Wei Expires: December 12, 2006 [Page 15]