Using Self-Delimiting Numeric Values in Protocols
RFC 6256

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Internet Research Task Force (IRTF)                              W. Eddy
Request for Comments: 6256                                   MTI Systems
Category: Informational                                        E. Davies
ISSN: 2070-1721                                         Folly Consulting
                                                                May 2011

           Using Self-Delimiting Numeric Values in Protocols

Abstract

   Self-Delimiting Numeric Values (SDNVs) have recently been introduced
   as a field type in proposed Delay-Tolerant Networking protocols.
   SDNVs encode an arbitrary-length non-negative integer or arbitrary-
   length bitstring with minimum overhead.  They are intended to provide
   protocol flexibility without sacrificing economy and to assist in
   future-proofing protocols under development.  This document describes
   formats and algorithms for SDNV encoding and decoding, along with
   notes on implementation and usage.  This document is a product of the
   Delay-Tolerant Networking Research Group and has been reviewed by
   that group.  No objections to its publication as an RFC were raised.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Research Task Force
   (IRTF).  The IRTF publishes the results of Internet-related research
   and development activities.  These results might not be suitable for
   deployment.  This RFC represents the consensus of the Delay-Tolerant
   Networking Research Group of the Internet Research Task Force (IRTF).
   Documents approved for publication by the IRSG are not a candidate
   for any level of Internet Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6256.

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RFC 6256                       Using SDNVs                      May 2011

Copyright Notice

   Copyright (c) 2011 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
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.

Table of Contents

   1. Introduction ....................................................2
      1.1. Problems with Fixed-Value Fields ...........................3
      1.2. SDNVs for DTN Protocols ....................................4
      1.3. SDNV Usage .................................................5
   2. Definition of SDNVs .............................................6
   3. Basic Algorithms ................................................8
      3.1. Encoding Algorithm .........................................8
      3.2. Decoding Algorithm .........................................9
      3.3. Limitations of Implementations ............................10
   4. Comparison to Alternatives .....................................10
   5. Security Considerations ........................................13
   6. Acknowledgements ...............................................13
   7. Informative References .........................................14
   Appendix A. SDNV Python Source Code ...............................15

1.  Introduction

   This document is a product of the Internet Research Task Force (IRTF)
   Delay-Tolerant Networking (DTN) Research Group (DTNRG).  The document
   has received review and support within the DTNRG, as discussed in the
   Acknowledgements section of this document.

   This document begins by describing the drawbacks of using fixed-width
   protocol fields.  It then provides some background on the Self-
   Delimiting Numeric Values (SDNVs) proposed for use in DTN protocols,
   and motivates their potential applicability in other networking
   protocols.  The DTNRG has created SDNVs to meet the challenges it
   attempts to solve, and it has been noted that SDNVs closely resemble
   certain constructs within ASN.1 and even older ITU protocols, so the
   problems are not new or unique to DTN.  SDNVs focus strictly on
   numeric values or bitstrings, while other mechanisms have been
   developed for encoding more complex data structures, such as ASN.1

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RFC 6256                       Using SDNVs                      May 2011

   encoding rules and Haverty's Message Services Data Transmission
   Protocol (MSDTP) [RFC0713].  Because of this focus, SDNVs can be
   quickly implemented with only a small amount of code.

   SDNVs are tersely defined in both the Bundle Protocol [RFC5050] and