Describing Protocol Data Units with Augmented Packet Header Diagrams
draft-mcquistin-augmented-ascii-diagrams-06

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Network Working Group                                       S. McQuistin
Internet-Draft                                                   V. Band
Intended status: Experimental                                   D. Jacob
Expires: 14 January 2021                                   C. S. Perkins
                                                   University of Glasgow
                                                            13 July 2020

  Describing Protocol Data Units with Augmented Packet Header Diagrams
              draft-mcquistin-augmented-ascii-diagrams-06

Abstract

   This document describes a machine-readable format for specifying the
   syntax of protocol data units within a protocol specification.  This
   format is comprised of a consistently formatted packet header
   diagram, followed by structured explanatory text.  It is designed to
   maintain human readability while enabling support for automated
   parser generation from the specification document.  This document is
   itself an example of how the format can be used.

Status of This Memo

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   This Internet-Draft will expire on 14 January 2021.

Copyright Notice

   Copyright (c) 2020 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   Please review these documents carefully, as they describe your rights
   and restrictions with respect to this document.  Code Components

McQuistin, et al.        Expires 14 January 2021                [Page 1]
Internet-Draft          Augmented Packet Diagrams              July 2020

   extracted from this document must include Simplified BSD License text
   as described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Background  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     2.1.  Limitations of Current Packet Format Diagrams . . . . . .   4
     2.2.  Formal languages in standards documents . . . . . . . . .   7
   3.  Design Principles . . . . . . . . . . . . . . . . . . . . . .   7
   4.  Augmented Packet Header Diagrams  . . . . . . . . . . . . . .  10
     4.1.  PDUs with Fixed and Variable-Width Fields . . . . . . . .  10
     4.2.  PDUs That Cross-Reference Previously Defined Fields . . .  13
     4.3.  PDUs with Non-Contiguous Fields . . . . . . . . . . . . .  15
     4.4.  PDUs with Constraints on Field Values . . . . . . . . . .  16
     4.5.  PDUs That Extend Sub-Structures . . . . . . . . . . . . .  17
     4.6.  Storing Data for Parsing  . . . . . . . . . . . . . . . .  18
     4.7.  Connecting Structures with Functions  . . . . . . . . . .  19
     4.8.  Specifying Enumerated Types . . . . . . . . . . . . . . .  20
     4.9.  Specifying Protocol Data Units  . . . . . . . . . . . . .  21
     4.10. Importing PDU Definitions from Other Documents  . . . . .  22
   5.  Open Issues . . . . . . . . . . . . . . . . . . . . . . . . .  22
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  22
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  22
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  23
   9.  Informative References  . . . . . . . . . . . . . . . . . . .  23
   Appendix A.  ABNF specification . . . . . . . . . . . . . . . . .  25
     A.1.  Constraint Expressions  . . . . . . . . . . . . . . . . .  25
     A.2.  Augmented packet diagrams . . . . . . . . . . . . . . . .  25
   Appendix B.  Source code repository . . . . . . . . . . . . . . .  25
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  26

1.  Introduction

   Packet header diagrams have become a widely used format for
   describing the syntax of binary protocols.  In otherwise largely
   textual documents, they allow for the visualisation of packet
   formats, reducing human error, and aiding in the implementation of
   parsers for the protocols that they specify.

   Figure 1 gives an example of how packet header diagrams are used to
   define binary protocol formats.  The format has an obvious structure: