AT&T's Error Resilient Video Transmission Technique
RFC 2448

Document Type RFC - Informational (November 1998; No errata)
Was draft-civanlar-hplp (individual)
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Network Working Group                                        M. Civanlar
Request for Comments: 2448                                       G. Cash
Category: Informational                                       B. Haskell
                                                      AT&T Labs-Research
                                                           November 1998

          AT&T's Error Resilient Video Transmission Technique

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (1998).  All Rights Reserved.

Abstract

   This document describes a set of techniques for packet loss resilient
   transmission of compressed video bitstreams based on reliable
   delivery of their vital information-carrying segments. The described
   techniques can be used over packet networks without packet
   prioritization. These techniques are related to AT&T/Lucent patents
   [1, 2].

1. Introduction

   It is well known that every bit in a compressed video bitstream is
   not equal. Some bits belong to segments defining vital information
   such as picture types, quantization values, parameter ranges, average
   intensity values for image blocks, etc. When transporting compressed
   video bitstreams over packet networks, packet losses from such
   segments cause a much longer lasting and severe degradation on the
   output of a decoder than that caused by packet losses from other
   segments. We will call the vital information-carrying segments "High
   Priority (HP)" segments. The rest of the bitstream consists of "Low
   Priority (LP)" segments. Clearly, the video outputs resulting from
   transport techniques that protect the HP segments against packet
   losses are more resilient to packet losses in general.

   Protection of the HP segments can be accomplished in many ways. These
   include:

      - redundant transmission of the HP segments as described
        in [3] for MPEG RTP payloads

Civanlar, et. al.            Informational                      [Page 1]
RFC 2448                AT&T's Error Resilient             November 1998

      - using forward error correction (FEC) techniques
      - transmitting HP segments over reserved channels or using
        differentiated services.

   Both redundant transmission and FEC techniques increase the bandwidth
   needed to transmit the compressed video bitstream. FEC techniques
   increase the effectiveness of this additional bandwidth for packet
   loss protection at the expense of increased processing at the
   receiver and the transmitter ends and increased overall delay. Using
   channel reservations or differentiated services based approaches may
   be the best solutions for protecting the HP segments but, they
   require network infrastructure changes.

   This document outlines another set of HP segment protection
   techniques based on AT&T/Lucent patents [1, 2] that can be used for
   reliable video transmission over packet networks without a built-in
   prioritization mechanism. These techniques use reliable transport
   protocols and "out-of-band" delivery approaches. In this context, the
   term "out-of-band" is used to imply information transmission means
   other than those used for transmitting the main video stream.  The
   details of these techniques are discussed in the following sections.
   An implementation of these, as applied to MPEG-2 video transmission
   over IP networks, is described in [4].

   The IESG/IETF take no position regarding the validity or scope of any
   intellectual property right or other rights that might be claimed to
   pertain to the implementation or use of the technology, or the extent
   to which any license under such rights might or might not be
   available.  See the IETF IPR web page at http://www.ietf.org/ipr.html
   for any additional information that has been forwarded to the IETF.

2. Identification of the HP segments

   The classification of a part of a video bitstream as an HP segment
   depends on two factors.  The first one is the encoding algorithm used
   in compressing the video data. It is impossible to segment a
   compressed video bitstream without knowing the syntax and the
   semantics of the encoding algorithm. The second factor is the
   determination of a compromise between the HP segment size and the
   corresponding loss resilience. As the segment size increases, so does
   the loss resilience.  On the other hand, it may not be feasible to
   deliver large HP segments reliably.

   As an example, the "data partitioning" method of the MPEG-2 standard
   [5] defines the syntax and semantics for one particular way of
   partitioning an MPEG-2 encoded video bitstream into HP and LP
   segments.  In data partitioning, the smallest useful HP segment can
   be selected to contain only the header information, which is usually
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