LPWAN Static Context Header Compression (SCHC) for CoAP

Document Type Active Internet-Draft (lpwan WG)
Last updated 2017-03-10
Replaces draft-toutain-lpwan-coap-static-context-hc
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lpwan Working Group                                          A. Minaburo
Internet-Draft                                                    Acklio
Intended status: Informational                                L. Toutain
Expires: September 11, 2017      Institut MINES TELECOM ; IMT Atlantique
                                                          March 10, 2017

        LPWAN Static Context Header Compression (SCHC) for CoAP


   This draft discusses the way SCHC header compression can be applied
   to CoAP headers in an LPWAN flow regarding the generated traffic.
   CoAP protocol differs from IPv6 and UDP protocols because the CoAP
   Header has a flexible header due to variable options.  Another
   important difference is the asymmetric format in the header
   information used in the request and the response packets.  This draft
   shows that the Client and the Server do not uses the same fields and
   how the SCHC header compression can be used.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on September 11, 2017.

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   Copyright (c) 2017 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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Internet-Draft           LPWAN CoAP compression               March 2017

   to this document.  Code Components extracted from this document must
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   described in the Simplified BSD License.

1.  Introduction

   [I-D.toutain-lpwan-ipv6-static-context-hc] defines a header
   compression mechanism for LPWAN network based on a static context.
   Where the context is said static since the element values composing
   the context are not learned during the packet exchanges but are
   previously defined.  The context(s) is(are) known by both ends before

   A context is composed of a set of rules (contexts) that are
   referenced by Rule IDs (identifiers).  A rule describes the header
   fields with some associated Target Values (TV).  A Matching Operator
   (MO) is associated to each header field description.  The rule is
   selected if all the MOs fit the TVs.  In that case, a Compression
   Decompression Function (CDF) associated to each field defines the
   link between the compressed and decompressed value for each of the
   header fields.

   This draft discusses the way SCHC can be applied to CoAP headers, how
   to extend MOs to match a specific element when several fields of the
   same type are presented in the header.  It also introduces the notion
   of bidirectional or unidirectional (upstream and downstream) fields.

2.  CoAP Compressing

   CoAP [RFC7252] is an implementation of the REST architecture for
   constrained devices.  Gateway between CoAP and HTTP can be easily
   built since both protocols uses the same address space (URL), caching
   mechanisms and methods.

   Nevertheless, if limited, the size of a CoAP header may be too large
   for LPWAN constraints and some compression may be needed to reduce
   the header size.  CoAP compression is not straightforward.  Some
   differences between IPv6/UDP and CoAP can be highlighted.  CoAP
   differs from IPv6 and UDP protocols in the following

   o  IPv6 and UDP are symmetrical protocols.  The same fields are found
      in the request and in the response, only position in the header
      may change (e.g. source and destination fields).  A CoAP request
      is different from an response.  For example, the URI-path option
      is mandatory in the request and is not found in the response.

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