RObust Header Compression (ROHC): Terminology and Channel Mapping Examples
RFC 3759

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Network Working Group                                       L-E. Jonsson
Request for Comments: 3759                                      Ericsson
Updates: 3095                                                 April 2004
Category: Informational

                   RObust Header Compression (ROHC):
                Terminology and Channel Mapping Examples

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 (2004).  All Rights Reserved.

Abstract

   This document aims to clarify terms and concepts presented in RFC
   3095.  RFC 3095 defines a Proposed Standard framework with profiles
   for RObust Header Compression (ROHC).  The standard introduces
   various concepts which might be difficult to understand and
   especially to relate correctly to the surrounding environments where
   header compression may be used.  This document aims at clarifying
   these aspects of ROHC, discussing terms such as ROHC instances, ROHC
   channels, ROHC feedback, and ROHC contexts, and how these terms
   relate to other terms, like network elements and IP interfaces,
   commonly used, for example, when addressing MIB issues.

Jonsson                      Informational                      [Page 1]
RFC 3759     ROHC Terminology and Channel Mapping Examples    April 2004

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  2
   2.  Terminology. . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  ROHC External Terminology. . . . . . . . . . . . . . . . . . .  6
       3.1.  Network Elements and IP Interfaces . . . . . . . . . . .  6
       3.2.  Channels . . . . . . . . . . . . . . . . . . . . . . . .  7
       3.3.  A Unidirectional Point-to-Point Link Example . . . . . .  8
       3.4.  A Bi-directional Point-to-Point Link Example . . . . . .  8
       3.5.  A Bi-directional Multipoint Link Example . . . . . . . .  9
       3.6.  A Multi-Channel Point-to-Point Link Example. . . . . . .  9
   4.  ROHC Instances . . . . . . . . . . . . . . . . . . . . . . . . 10
       4.1.  ROHC Compressors . . . . . . . . . . . . . . . . . . . . 11
       4.2.  ROHC Decompressors . . . . . . . . . . . . . . . . . . . 12
   5.  ROHC Channels. . . . . . . . . . . . . . . . . . . . . . . . . 13
   6.  ROHC Feedback Channels . . . . . . . . . . . . . . . . . . . . 14
       6.1.  Single-Channel Dedicated ROHC FB Channel Example . . . . 14
       6.2.  Piggybacked/Interspersed ROHC FB Channel Example . . . . 15
       6.3.  Dual-Channel Dedicated ROHC FB Channel Example . . . . . 16
   7.  ROHC Contexts. . . . . . . . . . . . . . . . . . . . . . . . . 17
   8.  Summary. . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
   9.  Implementation Implications. . . . . . . . . . . . . . . . . . 18
   10. Security Considerations. . . . . . . . . . . . . . . . . . . . 19
   11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 19
   12. Informative References . . . . . . . . . . . . . . . . . . . . 19
   13. Author's Address . . . . . . . . . . . . . . . . . . . . . . . 19
   14. Full Copyright Statement . . . . . . . . . . . . . . . . . . . 20

1.  Introduction

   In RFC 3095, the RObust Header Compression (ROHC) standard framework
   is defined, along with 4 compression profiles [RFC-3095].  Various
   concepts are introduced within the standard that are not all very
   extensively defined and described, which can easily be an obstacle
   when trying to understand the standard.  This can especially be the
   case when one considers how the various parts of ROHC relate to the
   surrounding environments where header compression may be used.

   The purpose of this document is to clarify these aspects of ROHC
   through examples and additional terminology, discussing terms such as
   ROHC instances, ROHC channels, ROHC feedback, and ROHC contexts.
   This especially means to clarify how these terms relate to other
   terms, such as network elements and IP interfaces, which are commonly
   used for example when addressing MIB issues.  One explicit goal of
   this document is to support and simplify the ROHC MIB development
   work.

Jonsson                      Informational                      [Page 2]
RFC 3759     ROHC Terminology and Channel Mapping Examples    April 2004

   The main part of this document, sections 3 to 8, focuses on
   clarifying the conceptual aspects, entity relationships, and
   terminology of ROHC [RFC-3095].  Section 9 explains some
   implementation implications that arise from these conceptual aspects.

2.  Terminology

   ROHC instance

      A logical entity that performs header compression or decompression
      according to one or several ROHC profiles can be referred to as a
      ROHC instance.  A ROHC instance is either a ROHC compressor