Block-wise transfers in CoAP
draft-ietf-core-block-21

Document Type Active Internet-Draft (core WG)
Last updated 2016-08-01 (latest revision 2016-07-08)
Replaces draft-bormann-core-coap-block
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Stream WG state Submitted to IESG for Publication Oct 2013
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CoRE Working Group                                            C. Bormann
Internet-Draft                                   Universitaet Bremen TZI
Updates: 7252 (if approved)                               Z. Shelby, Ed.
Intended status: Standards Track                                     ARM
Expires: January 9, 2017                                   July 08, 2016

                      Block-wise transfers in CoAP
                        draft-ietf-core-block-21

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.

   A CoAP implementation that does not support these options generally
   is limited in the size of the representations that can be exchanged.
   There is therefore an expectation that the Block options are very
   widely implemented in CoAP implementations, which is why this
   specification is listed as "updating" RFC 7252.

Bormann & Shelby         Expires January 9, 2017                [Page 1]
Internet-Draft        Block-wise transfers in CoAP             July 2016

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on January 9, 2017.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Block-wise transfers  . . . . . . . . . . . . . . . . . . . .   6
     2.1.  The Block2 and Block1 Options . . . . . . . . . . . . . .   7
     2.2.  Structure of a Block Option . . . . . . . . . . . . . . .   7
     2.3.  Block Options in Requests and Responses . . . . . . . . .   9
     2.4.  Using the Block2 Option . . . . . . . . . . . . . . . . .  11
     2.5.  Using the Block1 Option . . . . . . . . . . . . . . . . .  13
     2.6.  Combining Block-wise Transfers with the Observe Option  .  14
     2.7.  Combining Block1 and Block2 . . . . . . . . . . . . . . .  15
     2.8.  Combining Block2 with Multicast . . . . . . . . . . . . .  15
     2.9.  Response Codes  . . . . . . . . . . . . . . . . . . . . .  16
       2.9.1.  2.31 Continue . . . . . . . . . . . . . . . . . . . .  16
       2.9.2.  4.08 Request Entity Incomplete  . . . . . . . . . . .  16
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