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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