Formal Notation for RObust Header Compression (ROHC-FN)
RFC 4997

Network Working Group                                         R. Finking
Request for Comments: 4997                   Siemens/Roke Manor Research
Category: Standards Track                                   G. Pelletier
                                                                Ericsson
                                                               July 2007

        Formal Notation for RObust Header Compression (ROHC-FN)

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 defines Robust Header Compression - Formal Notation
   (ROHC-FN), a formal notation to specify field encodings for
   compressed formats when defining new profiles within the ROHC
   framework.  ROHC-FN offers a library of encoding methods that are
   often used in ROHC profiles and can thereby help to simplify future
   profile development work.

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Overview of ROHC-FN  . . . . . . . . . . . . . . . . . . . . .  5
     3.1.  Scope of the Formal Notation . . . . . . . . . . . . . . .  6
     3.2.  Fundamentals of the Formal Notation  . . . . . . . . . . .  7
       3.2.1.  Fields and Encodings . . . . . . . . . . . . . . . . .  7
       3.2.2.  Formats and Encoding Methods . . . . . . . . . . . . .  9
     3.3.  Example Using IPv4 . . . . . . . . . . . . . . . . . . . . 11
   4.  Normative Definition of ROHC-FN  . . . . . . . . . . . . . . . 13
     4.1.  Structure of a Specification . . . . . . . . . . . . . . . 13
     4.2.  Identifiers  . . . . . . . . . . . . . . . . . . . . . . . 14
     4.3.  Constant Definitions . . . . . . . . . . . . . . . . . . . 15
     4.4.  Fields . . . . . . . . . . . . . . . . . . . . . . . . . . 16
       4.4.1.  Attribute References . . . . . . . . . . . . . . . . . 17
       4.4.2.  Representation of Field Values . . . . . . . . . . . . 17

Finking & Pelletier         Standards Track                     [Page 1]
RFC 4997                        ROHC-FN                        July 2007

     4.5.  Grouping of Fields . . . . . . . . . . . . . . . . . . . . 17
     4.6.  "THIS" . . . . . . . . . . . . . . . . . . . . . . . . . . 18
     4.7.  Expressions  . . . . . . . . . . . . . . . . . . . . . . . 19
       4.7.1.  Integer Literals . . . . . . . . . . . . . . . . . . . 20
       4.7.2.  Integer Operators  . . . . . . . . . . . . . . . . . . 20
       4.7.3.  Boolean Literals . . . . . . . . . . . . . . . . . . . 20
       4.7.4.  Boolean Operators  . . . . . . . . . . . . . . . . . . 20
       4.7.5.  Comparison Operators . . . . . . . . . . . . . . . . . 21
     4.8.  Comments . . . . . . . . . . . . . . . . . . . . . . . . . 21
     4.9.  "ENFORCE" Statements . . . . . . . . . . . . . . . . . . . 22
     4.10. Formal Specification of Field Lengths  . . . . . . . . . . 23
     4.11. Library of Encoding Methods  . . . . . . . . . . . . . . . 24
       4.11.1. uncompressed_value . . . . . . . . . . . . . . . . . . 24
       4.11.2. compressed_value . . . . . . . . . . . . . . . . . . . 25
       4.11.3. irregular  . . . . . . . . . . . . . . . . . . . . . . 26
       4.11.4. static . . . . . . . . . . . . . . . . . . . . . . . . 27
       4.11.5. lsb  . . . . . . . . . . . . . . . . . . . . . . . . . 27
       4.11.6. crc  . . . . . . . . . . . . . . . . . . . . . . . . . 29
     4.12. Definition of Encoding Methods . . . . . . . . . . . . . . 29
       4.12.1. Structure  . . . . . . . . . . . . . . . . . . . . . . 30
       4.12.2. Arguments  . . . . . . . . . . . . . . . . . . . . . . 37
       4.12.3. Multiple Formats . . . . . . . . . . . . . . . . . . . 38
     4.13. Profile-Specific Encoding Methods  . . . . . . . . . . . . 40
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 41
   6.  Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 41
   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 41
   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 42
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 42
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 42
   Appendix A.  Formal Syntax of ROHC-FN  . . . . . . . . . . . . . . 43
   Appendix B.  Bit-level Worked Example  . . . . . . . . . . . . . . 45
     B.1.  Example Packet Format  . . . . . . . . . . . . . . . . . . 45