RObust Header Compression (ROHC): ROHC over Channels That Can Reorder Packets
RFC 4224

 
Document Type RFC - Informational (January 2006; No errata)
Last updated 2013-03-02
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IESG IESG state RFC 4224 (Informational)
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Responsible AD Allison Mankin
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Network Working Group                                       G. Pelletier
Request for Comments: 4224                                  L-E. Jonsson
Category: Informational                                      K. Sandlund
                                                                Ericsson
                                                            January 2006

                   RObust Header Compression (ROHC):
              ROHC over Channels That Can Reorder Packets

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 (2006).

Abstract

   RObust Header Compression (ROHC), RFC 3095, defines a framework for
   header compression, along with a number of compression protocols
   (profiles).  One operating assumption for the profiles defined in RFC
   3095 is that the channel between compressor and decompressor is
   required to maintain packet ordering.  This document discusses
   aspects of using ROHC over channels that can reorder packets.  It
   provides guidelines on how to implement existing profiles over such
   channels, as well as suggestions for the design of new profiles.

Pelletier, et al.            Informational                      [Page 1]
RFC 4224             ROHC over Reordering Channels          January 2006

Table of Contents

   1. Introduction ....................................................3
   2. Terminology .....................................................4
   3. Applicability of This Document to ROHC Profiles .................5
      3.1. Profiles within Scope ......................................5
      3.2. Profiles with Special Considerations .......................5
      3.3. Profiles Incompatible with Reordering ......................6
   4. Background ......................................................6
      4.1. Reordering Channels ........................................6
      4.2. Robustness Principles of ROHC ..............................6
           4.2.1. Optimistic Approach (U/O-mode) ......................7
           4.2.2. Secure Reference Principle (R-mode) .................7
   5. Problem Description .............................................7
      5.1. ROHC and Reordering Channels ...............................7
           5.1.1. LSB Interpretation Interval and Reordering ..........7
           5.1.2. Reordering of Packets in R-mode .....................9
                  5.1.2.1. Updating Packets ...........................9
                  5.1.2.2. Non-Updating Packets ......................10
           5.1.3. Reordering of Packets in U/O-mode ..................10
           5.1.4. Reordering on the Feedback Channel .................11
           5.1.5. List Compression ...................................11
           5.1.6. Reordering and Mode Transitions ....................12
      5.2. Consequences of Reordering ................................13
           5.2.1. Functionality Incompatible with Reordering .........13
           5.2.2. Context Damage (Loss of Synchronization) ...........13
           5.2.3. Detected Decompression Failures (U/O/R-mode) .......13
           5.2.4. Undetected Decompression Failures (R-mode only) ....14
   6. Making ROHC Tolerant against Reordering ........................14
      6.1. Properties of ROHC Implementations ........................14
           6.1.1. Compressing Headers with Robustness against
                  Reordering .........................................14
                  6.1.1.1. Reordering and the Optimistic Approach ....15
                  6.1.1.2. Reordering and the Secure
                           Reference Principle .......................15
                  6.1.1.3. Robust Selection of Compressed Header .....15
           6.1.2. Implementing a Reordering-Tolerant Decompressor ....16
                  6.1.2.1. Decompressor Feedback Considerations ......16
                  6.1.2.2. Considerations for Local Repair
                           Mechanisms ................................17
      6.2. Specifying ROHC Profiles with Robustness against
           Reordering ................................................17
           6.2.1. Profiles with Interpretation Interval
                  Offset p = -1 ......................................17
           6.2.2. Modifying the Interpretation Interval Offset .......18
                  6.2.2.1. Example Profile for Handling Reordering ...18
                  6.2.2.2. Defining the Values of p for New
                           Profiles ..................................18

Pelletier, et al.            Informational                      [Page 2]
RFC 4224             ROHC over Reordering Channels          January 2006
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