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
