RObust Header Compression Version 2 (ROHCv2): Profiles for RTP, UDP, IP, ESP and UDP-Lite
RFC 5225
Network Working Group G. Pelletier
Request for Comments: 5225 K. Sandlund
Category: Standards Track Ericsson
April 2008
RObust Header Compression Version 2 (ROHCv2):
Profiles for RTP, UDP, IP, ESP and UDP-Lite
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Abstract
This document specifies ROHC (Robust Header Compression) profiles
that efficiently compress RTP/UDP/IP (Real-Time Transport Protocol,
User Datagram Protocol, Internet Protocol), RTP/UDP-Lite/IP (User
Datagram Protocol Lite), UDP/IP, UDP-Lite/IP, IP and ESP/IP
(Encapsulating Security Payload) headers.
This specification defines a second version of the profiles found in
RFC 3095, RFC 3843 and RFC 4019; it supersedes their definition, but
does not obsolete them.
The ROHCv2 profiles introduce a number of simplifications to the
rules and algorithms that govern the behavior of the compression
endpoints. It also defines robustness mechanisms that may be used by
a compressor implementation to increase the probability of
decompression success when packets can be lost and/or reordered on
the ROHC channel. Finally, the ROHCv2 profiles define their own
specific set of header formats, using the ROHC formal notation.
Pelletier & Sandlund Standards Track [Page 1]
RFC 5225 ROHCv2 Profiles April 2008
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4. Background (Informative) . . . . . . . . . . . . . . . . . . 7
4.1. Classification of Header Fields . . . . . . . . . . . . . 7
4.2. Improvements of ROHCv2 over RFC 3095 Profiles . . . . . . 8
4.3. Operational Characteristics of ROHCv2 Profiles . . . . . 10
5. Overview of the ROHCv2 Profiles (Informative) . . . . . . . . 10
5.1. Compressor Concepts . . . . . . . . . . . . . . . . . . . 11
5.1.1. Optimistic Approach . . . . . . . . . . . . . . . . . 11
5.1.2. Tradeoff between Robustness to Losses and to
Reordering . . . . . . . . . . . . . . . . . . . . . 11
5.1.3. Interactions with the Decompressor Context . . . . . 13
5.2. Decompressor Concepts . . . . . . . . . . . . . . . . . . 14
5.2.1. Decompressor State Machine . . . . . . . . . . . . . 14
5.2.2. Decompressor Context Management . . . . . . . . . . . 17
5.2.3. Feedback Logic . . . . . . . . . . . . . . . . . . . 19
6. ROHCv2 Profiles (Normative) . . . . . . . . . . . . . . . . . 19
6.1. Channel Parameters, Segmentation, and Reordering . . . . 19
6.2. Profile Operation, Per-context . . . . . . . . . . . . . 20
6.3. Control Fields . . . . . . . . . . . . . . . . . . . . . 21
6.3.1. Master Sequence Number (MSN) . . . . . . . . . . . . 21
6.3.2. Reordering Ratio . . . . . . . . . . . . . . . . . . 21
6.3.3. IP-ID Behavior . . . . . . . . . . . . . . . . . . . 22
6.3.4. UDP-Lite Coverage Behavior . . . . . . . . . . . . . 22
6.3.5. Timestamp Stride . . . . . . . . . . . . . . . . . . 22
6.3.6. Time Stride . . . . . . . . . . . . . . . . . . . . . 22
6.3.7. CRC-3 for Control Fields . . . . . . . . . . . . . . 23
6.4. Reconstruction and Verification . . . . . . . . . . . . . 23
6.5. Compressed Header Chains . . . . . . . . . . . . . . . . 24
6.6. Header Formats and Encoding Methods . . . . . . . . . . . 25
6.6.1. baseheader_extension_headers . . . . . . . . . . . . 26
6.6.2. baseheader_outer_headers . . . . . . . . . . . . . . 26
6.6.3. inferred_udp_length . . . . . . . . . . . . . . . . . 26
6.6.4. inferred_ip_v4_header_checksum . . . . . . . . . . . 26
6.6.5. inferred_mine_header_checksum . . . . . . . . . . . . 27
6.6.6. inferred_ip_v4_length . . . . . . . . . . . . . . . . 28
6.6.7. inferred_ip_v6_length . . . . . . . . . . . . . . . . 28
6.6.8. Scaled RTP Timestamp Compression . . . . . . . . . . 29
6.6.9. timer_based_lsb . . . . . . . . . . . . . . . . . . . 30
6.6.10. inferred_scaled_field . . . . . . . . . . . . . . . . 31
6.6.11. control_crc3_encoding . . . . . . . . . . . . . . . . 32
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