Block-Wise Transfers in the Constrained Application Protocol (CoAP)
RFC 7959
| Document | Type |
RFC - Proposed Standard
(August 2016; No errata)
Updates RFC 7252
Was draft-ietf-core-block (core WG)
|
|
|---|---|---|---|
| Last updated | 2016-08-26 | ||
| Replaces | draft-bormann-core-coap-block | ||
| Stream | IETF | ||
| Formats | plain text pdf html bibtex | ||
| Stream | WG state | Submitted to IESG for Publication Oct 2013 | |
| Document shepherd | Matthias Kovatsch | ||
| Shepherd write-up | Show (last changed 2015-11-02) | ||
| IESG | IESG state | RFC 7959 (Proposed Standard) | |
| Consensus Boilerplate | Yes | ||
| Telechat date | |||
| Responsible AD | Alexey Melnikov | ||
| Send notices to | (None) | ||
| IANA | IANA review state | Version Changed - Review Needed | |
| IANA action state | RFC-Ed-Ack | ||
Internet Engineering Task Force (IETF) C. Bormann Request for Comments: 7959 Universitaet Bremen TZI Updates: 7252 Z. Shelby, Ed. Category: Standards Track ARM ISSN: 2070-1721 August 2016 Block-Wise Transfers in the Constrained Application Protocol (CoAP) Abstract The Constrained Application Protocol (CoAP) is a RESTful transfer protocol for constrained nodes and networks. Basic CoAP messages work well for small payloads from sensors and actuators; however, applications will need to transfer larger payloads occasionally -- for instance, for firmware updates. In contrast to HTTP, where TCP does the grunt work of segmenting and resequencing, CoAP is based on datagram transports such as UDP or Datagram Transport Layer Security (DTLS). These transports only offer fragmentation, which is even more problematic in constrained nodes and networks, limiting the maximum size of resource representations that can practically be transferred. 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. Essentially, 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, so there is an expectation that the Block options will be widely used in CoAP implementations. Therefore, this specification updates RFC 7252. Bormann & Shelby Standards Track [Page 1] RFC 7959 Block-Wise Transfer in CoAP August 2016 Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc7959. Copyright Notice Copyright (c) 2016 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. Bormann & Shelby Standards Track [Page 2] RFC 7959 Block-Wise Transfer in CoAP August 2016 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Block-Wise Transfers . . . . . . . . . . . . . . . . . . . . 6 2.1. The Block2 and Block1 Options . . . . . . . . . . . . . . 7 2.2. Structure of a Block Option . . . . . . . . . . . . . . . 8 2.3. Block Options in Requests and Responses . . . . . . . . . 10 2.4. Using the Block2 Option . . . . . . . . . . . . . . . . . 12 2.5. Using the Block1 Option . . . . . . . . . . . . . . . . . 14 2.6. Combining Block-Wise Transfers with the Observe Option . 15 2.7. Combining Block1 and Block2 . . . . . . . . . . . . . . . 16 2.8. Combining Block2 with Multicast . . . . . . . . . . . . . 16 2.9. Response Codes . . . . . . . . . . . . . . . . . . . . . 17 2.9.1. 2.31 Continue . . . . . . . . . . . . . . . . . . . . 17 2.9.2. 4.08 Request Entity Incomplete . . . . . . . . . . . 17 2.9.3. 4.13 Request Entity Too Large . . . . . . . . . . . . 17 2.10. Caching Considerations . . . . . . . . . . . . . . . . . 18 3. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 18Show full document text