RObust Header Compression (ROHC): A Profile for TCP/IP (ROHC-TCP)
RFC 4996

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Network Working Group                                       G. Pelletier
Request for Comments: 4996                                   K. Sandlund
Category: Standards Track                                       Ericsson
                                                            L-E. Jonsson

                                                                 M. West
                                                      Siemens/Roke Manor
                                                               July 2007

   RObust Header Compression (ROHC): A Profile for TCP/IP (ROHC-TCP)

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.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   This document specifies a ROHC (Robust Header Compression) profile
   for compression of TCP/IP packets.  The profile, called ROHC-TCP,
   provides efficient and robust compression of TCP headers, including
   frequently used TCP options such as SACK (Selective Acknowledgments)
   and Timestamps.

   ROHC-TCP works well when used over links with significant error rates
   and long round-trip times.  For many bandwidth-limited links where
   header compression is essential, such characteristics are common.

Pelletier, et al.           Standards Track                     [Page 1]
RFC 4996                        ROHC-TCP                       July 2007

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Background . . . . . . . . . . . . . . . . . . . . . . . . . .  5
     3.1.  Existing TCP/IP Header Compression Schemes . . . . . . . .  5
     3.2.  Classification of TCP/IP Header Fields . . . . . . . . . .  6
   4.  Overview of the TCP/IP Profile (Informative) . . . . . . . . .  8
     4.1.  General Concepts . . . . . . . . . . . . . . . . . . . . .  8
     4.2.  Compressor and Decompressor Interactions . . . . . . . . .  8
       4.2.1.  Compressor Operation . . . . . . . . . . . . . . . . .  8
       4.2.2.  Decompressor Feedback  . . . . . . . . . . . . . . . .  9
     4.3.  Packet Formats and Encoding Methods  . . . . . . . . . . .  9
       4.3.1.  Compressing TCP Options  . . . . . . . . . . . . . . . 10
       4.3.2.  Compressing Extension Headers  . . . . . . . . . . . . 10
     4.4.  Expected Compression Ratios with ROHC-TCP  . . . . . . . . 10
   5.  Compressor and Decompressor Logic (Normative)  . . . . . . . . 11
     5.1.  Context Initialization . . . . . . . . . . . . . . . . . . 11
     5.2.  Compressor Operation . . . . . . . . . . . . . . . . . . . 11
       5.2.1.  Compression Logic  . . . . . . . . . . . . . . . . . . 11
       5.2.2.  Feedback Logic . . . . . . . . . . . . . . . . . . . . 13
       5.2.3.  Context Replication  . . . . . . . . . . . . . . . . . 14
     5.3.  Decompressor Operation . . . . . . . . . . . . . . . . . . 14
       5.3.1.  Decompressor States and Logic  . . . . . . . . . . . . 14
       5.3.2.  Feedback Logic . . . . . . . . . . . . . . . . . . . . 18
       5.3.3.  Context Replication  . . . . . . . . . . . . . . . . . 18
   6.  Encodings in ROHC-TCP (Normative)  . . . . . . . . . . . . . . 18
     6.1.  Control Fields in ROHC-TCP . . . . . . . . . . . . . . . . 18
       6.1.1.  Master Sequence Number (MSN) . . . . . . . . . . . . . 19
       6.1.2.  IP-ID Behavior . . . . . . . . . . . . . . . . . . . . 19
       6.1.3.  Explicit Congestion Notification (ECN) . . . . . . . . 20
     6.2.  Compressed Header Chains . . . . . . . . . . . . . . . . . 21
     6.3.  Compressing TCP Options with List Compression  . . . . . . 23
       6.3.1.  List Compression . . . . . . . . . . . . . . . . . . . 23
       6.3.2.  Table-Based Item Compression . . . . . . . . . . . . . 24
       6.3.3.  Encoding of Compressed Lists . . . . . . . . . . . . . 25
       6.3.4.  Item Table Mappings  . . . . . . . . . . . . . . . . . 26
       6.3.5.  Compressed Lists in Dynamic Chain  . . . . . . . . . . 28
       6.3.6.  Irregular Chain Items for TCP Options  . . . . . . . . 28
       6.3.7.  Replication of TCP Options . . . . . . . . . . . . . . 28
     6.4.  Profile-Specific Encoding Methods  . . . . . . . . . . . . 29
       6.4.1.  inferred_ip_v4_header_checksum . . . . . . . . . . . . 29
       6.4.2.  inferred_mine_header_checksum  . . . . . . . . . . . . 30
       6.4.3.  inferred_ip_v4_length  . . . . . . . . . . . . . . . . 30
       6.4.4.  inferred_ip_v6_length  . . . . . . . . . . . . . . . . 31
       6.4.5.  inferred_offset  . . . . . . . . . . . . . . . . . . . 31
       6.4.6.  baseheader_extension_headers . . . . . . . . . . . . . 31