RFC 3242 (rfc3242) - Page 2 of 21
RObust Header Compression (ROHC): A Link-Layer Assisted Profile for IP/UDP/RTP
Alternative Format: Original Text Document
RFC 3242 A Link-Layer Assisted ROHC RTP April 2002
4.2. Interfaces Towards the Assisting Layer..................11
4.2.1. Interface, Compressor to Assisting Layer.......11
4.2.2. Interface, Assisting Layer to Decompressor.....12
4.3. Optimistic Approach Agreement...........................13
4.4. Fast Context Initialization, IR Redefinition............13
4.5. Feedback Option, CV-REQUEST.............................14
4.6. Periodic Context Verification...........................15
4.7. Use of Context Identifier...............................15
5. Implementation Issues..........................................15
5.1. Implementation Parameters and Signals...................15
5.1.1. Implementation Parameters at the Compressor....16
5.1.2. Implementation Parameters at the Decompressor..17
5.2. Implementation over Various Link Technologies...........18
6. IANA Considerations............................................18
7. Security Considerations........................................18
8. Acknowledgements...............................................18
9. References.....................................................19
10. Authors' Addresses.............................................20
11. Full Copyright Statement.......................................21
1. Introduction
Header compression is a technique used to compress and transparently
decompress the header information of a packet on a per-hop basis,
utilizing redundancy within individual packets and between
consecutive packets within a packet stream. Over the years, several
protocols [VJHC, IPHC] have been developed to compress the network
and transport protocol headers [IPv4, IPv6, UDP, TCP], and these
schemes have been successful in improving efficiency over many wired
bottleneck links, such as modem connections over telephone networks.
In addition to IP, UDP, and TCP compression, an additional
compression scheme called Compressed RTP [CRTP] has been developed to
further improve compression efficiency for the case of real-time
traffic using the Real-Time Transport Protocol [RTP].
The schemes mentioned above have all been designed taking into
account normal assumptions about link characteristics, which
traditionally have been based on wired links only. However, with an
increasing number of wireless links in the Internet paths, these
assumptions are no longer generally valid. In wireless environments,
especially wide coverage cellular environments, relatively high error
rates are tolerated in order to allow efficient usage of the radio
resources. For real-time traffic, which is more sensitive to delays
than to errors, such operating conditions will be norm over, for
example, 3rd generation cellular links, and header compression must
therefore tolerate packet loss. However, with the previously
mentioned schemes, especially for real-time traffic compressed by
CRTP, high error rates have been shown to significantly degrade
Jonsson, et. al Standards Track