Blockwise transfers in CoAP
draft-ietf-core-block-11

The information below is for an old version of the document
Document Type Active Internet-Draft (core WG)
Last updated 2013-03-30
Replaces draft-bormann-core-coap-block
Stream IETF
Intended RFC status Proposed Standard
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Stream WG state WG Document Oct 2013
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Responsible AD Barry Leiba
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CoRE Working Group                                            C. Bormann
Internet-Draft                                   Universitaet Bremen TZI
Intended status: Standards Track                          Z. Shelby, Ed.
Expires: October 01, 2013                                      Sensinode
                                                          March 30, 2013

                      Blockwise transfers in CoAP
                        draft-ietf-core-block-11

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 -\u002D 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.

   The present revision -11 fixes one example and adds the text and
   examples about the Block/Observe interaction, taken from -observe.
   It also adds a couple of formatting bugs from the new xml2rfc.  The
   "grand rewrite" is next.

Status of This Memo

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

Bormann & Shelby        Expires October 01, 2013                [Page 1]
Internet-Draft        Blockwise transfers in CoAP             March 2013

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Block-wise transfers  . . . . . . . . . . . . . . . . . . . .   5
     2.1.  The Block 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.  Block2 and Initiative . . . . . . . . . . . . . . . . . .  13
   3.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . .  13
     3.1.  Block2 Examples . . . . . . . . . . . . . . . . . . . . .  13
     3.2.  Block1 Examples . . . . . . . . . . . . . . . . . . . . .  16
     3.3.  Combining Block1 and Block2 . . . . . . . . . . . . . . .  18
     3.4.  Combining Observe and Block2  . . . . . . . . . . . . . .  20
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