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Blockwise transfers in CoAP
draft-ietf-core-block-15

Document type: Active Internet-Draft (core WG)
Document stream: IETF
Last updated: 2014-07-23 (latest revision 2014-07-04)
Intended RFC status: Proposed Standard
Other versions: plain text, pdf, html

IETF State: In WG Last Call Oct 2013
Document shepherd: No shepherd assigned

IESG State: AD is watching
Responsible AD: Barry Leiba
Send notices to: core-chairs@tools.ietf.org, draft-ietf-core-block@tools.ietf.org

CoRE Working Group                                            C. Bormann
Internet-Draft                                   Universitaet Bremen TZI
Intended status: Standards Track                          Z. Shelby, Ed.
Expires: January 5, 2015                                             ARM
                                                           July 04, 2014

                      Blockwise transfers in CoAP
                        draft-ietf-core-block-15

Abstract

   CoAP is a RESTful transfer protocol for constrained nodes and
   networks.  Basic CoAP messages work well for the small payloads we
   expect from temperature sensors, light switches, and similar
   building-automation devices.  Occasionally, however, applications
   will need to transfer larger payloads -- for instance, for firmware
   updates.  With HTTP, TCP does the grunt work of slicing large
   payloads up into multiple packets and ensuring that they all arrive
   and are handled in the right order.

   CoAP is based on datagram transports such as UDP or DTLS, which
   limits the maximum size of resource representations that can be
   transferred without too much fragmentation.  Although UDP supports
   larger payloads through IP fragmentation, it is limited to 64 KiB
   and, more importantly, doesn't really work well for constrained
   applications and networks.

   Instead of relying on IP fragmentation, this specification extends
   basic CoAP with a pair of "Block" options, for transferring multiple
   blocks of information from a resource representation in multiple
   request-response pairs.  In many important cases, the Block options
   enable a server to be truly stateless: the server can handle each
   block transfer separately, with no need for a connection setup or
   other server-side memory of previous block transfers.

   In summary, the Block options provide a minimal way to transfer
   larger representations in a block-wise fashion.

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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

Bormann & Shelby         Expires January 5, 2015                [Page 1]
Internet-Draft         Blockwise transfers in CoAP             July 2014

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 5, 2015.

Copyright Notice

   Copyright (c) 2014 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.  Code Components 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  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Block-wise transfers  . . . . . . . . . . . . . . . . . . . .   5
     2.1.  The Block2 and Block1 Options . . . . . . . . . . . . . .   5
     2.2.  Structure of a Block Option . . . . . . . . . . . . . . .   6
     2.3.  Block Options in Requests and Responses . . . . . . . . .   8
     2.4.  Using the Block2 Option . . . . . . . . . . . . . . . . .  10
     2.5.  Using the Block1 Option . . . . . . . . . . . . . . . . .  11
     2.6.  Combining Blockwise Transfers with the Observe Option . .  12
     2.7.  Combining Block1 and Block2 . . . . . . . . . . . . . . .  13
     2.8.  Combining Block2 with Multicast . . . . . . . . . . . . .  13
     2.9.  Response Codes  . . . . . . . . . . . . . . . . . . . . .  14
       2.9.1.  2.31 Continue . . . . . . . . . . . . . . . . . . . .  14
       2.9.2.  4.08 Request Entity Incomplete  . . . . . . . . . . .  14
       2.9.3.  4.13 Request Entity Too Large . . . . . . . . . . . .  14
   3.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  15
     3.1.  Block2 Examples . . . . . . . . . . . . . . . . . . . . .  15
     3.2.  Block1 Examples . . . . . . . . . . . . . . . . . . . . .  19
     3.3.  Combining Block1 and Block2 . . . . . . . . . . . . . . .  20

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