Internet Engineering Task Force Michael F. Speer draft-speer-avt-layered-video-00.txt Sun Microsystems, Inc. Steven McCanne LBNL Date: March 1, 1996 Expires: Sept 1, 1996 RTP usage with Layered Multimedia Streams Status of this Memo This document is an Internet Draft. 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. Internet Drafts may be updated, replaced, or obsoleted by other documents at any time. It is not appropriate to use Internet Drafts as reference material or to cite them other than as a ``working draft'' or ``work in progress.'' Please check the I-D abstract listing contained in each Internet Draft directory to learn the current status of this or any other Internet Draft. Distribution of this document is unlimited. Abstract This draft describes how one should make use of RTP (rfc1889) when employing layered media streams. This document is meant for implementors of internet multimedia applications that want to use RTP and layered media streams. draft-speer-mccanne-avt-layered-video-00.txt [Page 1]
INTERNET-DRAFT Layered Multimedia Streams March 1996 1 Introduction This memorandum describes how to use RTP (Real-Time Transport Protocol, rfc1889) with layered multimedia streams. 2 Layered Video Today, most multimedia applications place the responsibility of rate-adaptivity at the source. In multicast transmission, source-adaptation, as discussed in [3], leads to the source not being to meet the conflicting bandwidth requirements of the all receivers. This usually leads to the least-common denominator scenarios, where the smallest pipe in the network mesh dictates the quality and fidelity of the overall live multimedia "broadcast". If the responsibility of rate-adaptation is placed at the receivers, then heterogeneity of such media transmissions is achievable. One approach for moving rate-adaptation from the source to the receivers is to combine a layered source-coder with a layered transmission system. In the context of IP Multicast, Deering proposed a realization of this scheme where a source stripes the progressive layers of a hierarchically represented signal across multiple multicast groups [2]. Receivers can then adapt to network heterogeneity by controlling their reception bandwidth through IP Multicast group membership. In the case of video transmission, several approaches to the layered source-coding problem have been explored, including multirate JPEG [4], subband coding [6], and hierarchical vector quantization [1]. 3 RTP Usage The RTP specification [5] implicitly assumes that the underlying transport/network layer is monolithic. That is, a single RTP session is carried on a single underlying communications layer. However, the layered transmission system described above requires that the stream be partitioned across multiple underlying transport end-points. In RTP, each signal source is identified with a randomly allocated 32-bit source identifier (SRCID) that is unique only within a single session (a collision detection algorithm resolves conflicts). Additionally, each user is identified with a variable-length ``canonical name'' (CNAME) string that is globally unique. Data packets are identified only by SRCID, and periodically, each application broadcasts a binding between it's CNAME and SRCID. Thus, a receiver can collate streams across different sessions (identified by different SRCID's) using the level of indirection provided by the CNAME. Using this framework, we can readily handle layered compression formats by treating each layer as a distinct ``RTP session'' and distributing it on its own multicast group. This is the same approach draft-speer-mccanne-avt-layered-video-00.txt [Page 2]
INTERNET-DRAFT Layered Multimedia Streams March 1996 that the RTP uses to relate separate audio and video streams from a single user. However, the ``RTP session per layer'' approach adds unnecessary complexity. Not only does it force each receiver to manage all the CNAME/SRCID bindings, but it requires newly arrived receivers to wait for the binding advertisement before they can start decoding a stream. Another problem is that it creates new error recovery conditions for dealing with conflicting information arriving on the different sessions. We propose to extend RTP semantics. Our proposal is that a single SRCID space is used across all layers and that the core (base) layer be used for SRCID allocation and conflict resolution. With regard to RTCP, we propose that sender identification strings are redundant across all layers and thus should only be transmitted on the base layer. Other than the proposed semantics above, all other RTP rules and practices apply. draft-speer-mccanne-avt-layered-video-00.txt [Page 3]
INTERNET-DRAFT Layered Multimedia Streams March 1996 4 References 1. Chaddha, N., Wall, G., and Schmidt, B., "An End to End Software Only Scalable Video Delivery System", Proc. Fifth International Workshop on Network and OS Support for Digital Audio and Video (April, 1995) 2. Deering, S., Internet Multicast Routing: State of the Art and Open Research Issues, MICE Seminar, SICS, Stockholm (Oct 1993). 3. McCanne, S. and Jacobson, V., "Receiver-Driven Layered Multicast". Submitted to SigComm 1996. 4. Hoffman, D. and Speer, M., "Hierarchical Video Distribution over Internet-style Networks". Submitted to the IEEE International Conference on Image Processing (Sept. 1996) 5. Schulzrinne, H., Casner, S., Frederick, R., and Jacobson, V., "RTP: A Transport Protocol for Real-Time Applications", rfc1889. 6. Taubman, D. and Zakhor, A. "Multi-rate 3-D Subband Coding of Video". IEEE Transactions on Image Processing 3,5 (Sept 1994) 572-488. 5 Address of the Authors Michael F. Speer Sun Microsystems Computer Corporation 2550 Garcia Ave MailStop UMPK14-305 Mountain View, CA 94043 Voice: +1 415 786 6368 Fax: +1 415 786 6445 E-mail: michael.speer@eng.sun.com Steven McCanne M/S 50B-2239 Lawrence Berkeley National Laboratory One Cyclotron Road Berkeley, CA 94720 Voice: +1 510 486 7520 Fax: +1 510 486 6363 E-mail: mccanne@ee.lbl.gov draft-speer-mccanne-avt-layered-video-00.txt [Page 4]
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