Options for Repair of Streaming Media (RFC2354)
Original Publication Date: 1998-Jun-01
Included in the Prior Art Database: 2019-Feb-15
Internet Society Requests For Comment (RFCs)
C. Perkins: AUTHOR [+1]
This document summarizes a range of possible techniques for the repair of continuous media streams subject to packet loss. This memo provides information for the Internet community. This memo does not specify an Internet standard of any kind.
Network Working Group C. Perkins Request for Comments: 2354 O. Hodson Category: Informational University College London June 1998
Options for Repair of Streaming Media
Status of this Memo
This memo provides information for the Internet community. This memo does not specify an Internet standard of any kind. Distribution of this memo is unlimited.
Copyright (C) The Internet Society (1998). All Rights Reserved.
This document summarizes a range of possible techniques for the repair of continuous media streams subject to packet loss. The techniques discussed include redundant transmission, retransmission, interleaving and forward error correction. The range of applicability of these techniques is noted, together with the protocol requirements and dependencies.
A number of applications have emerged which use RTP/UDP transport to deliver continuous media streams. Due to the unreliable nature of UDP packet delivery, the quality of the received stream will be adversely affected by packet loss. A number of techniques exist by which the effects of packet loss may be repaired. These techniques have a wide range of applicability and require varying degrees of protocol support. In this document, a number of such techniques are discussed, and recommendations for their applicability made.
It should be noted that this document is introductory in nature, and does not attempt to be comprehensive. In particular, we restrict our discussion to repair techniques which require the involvement of the sender of a media stream, and do not discuss possibilities for receiver based repair.
For a more detailed survey, the reader is referred to .
Perkins & Hodson Informational [Page 1]
RFC 2354 Options for Repair of Streaming Media June 1998
2 Terminology and Protocol Framework
A unit is defined to be a timed interval of media data, typically derived from the workings of the media coder. A packet comprises one or more units, encapsulated for transmission over the network. For example, many audio coders operate on 20ms units, which are typically combined to produce 40ms or 80ms packets for transmission. The framework of RTP  is assumed. This implies that packets have a sequence number and timestamp. The sequence number denotes the order in which packets are transmitted, and is used to detect losses. The timestamp is used to determine the playout order of units. Most loss recovery schemes rely on units being sent out of order, so an application must use the RTP timestamp to schedule playout.
The use of RTP allows for several different media coders, with a payload type field being used to distinguish between these at the receiver. Some loss repair schemes send multiple copies of units, at different times and possibly with different encodings, to increase the probability that a receiver has something to decode. A receiver is assumed to have a ‘quality’ ranking of the differing encodings, and so is capable of choosing the ‘best’ un...