CoRE Working Group B. SilverajanInternet-Draft Tampere University of TechnologyIntended status: Informational March 9, 2015Expires: September 10, 2015CoAP Protocol Negotiationdraft-silverajan-core-coap-protocol-negotiation-00Abstract CoAP has been standardised as an application level REST-based protocol. This document introduces a way for CoAP clients and servers to interact with resources by agreeing upon alternate locations as well as transport and protocol configurations.Status of This Memo This Internet-Draft is submitted in full conformance with the provisions ofBCP 78 andBCP 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 athttp://datatracker.ietf.org/drafts/current/. 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 September 10, 2015.Copyright Notice Copyright (c) 2015 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject toBCP 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.Silverajan Expires September 10, 2015 [Page 1]
Internet-Draft CoAP Protocol Negotiation March 2015Table of Contents1. Introduction . . . . . . . . . . . . . . . . . . . . . . . .22. New Link Attribute and Relation types . . . . . . . . . . . .33. Examples . . . . . . . . . . . . . . . . . . . . . . . . . .34. IANA Considerations . . . . . . . . . . . . . . . . . . . . .55. Security Considerations . . . . . . . . . . . . . . . . . . .56. Acknowledgements . . . . . . . . . . . . . . . . . . . . . .57. References . . . . . . . . . . . . . . . . . . . . . . . . .57.1. Normative References . . . . . . . . . . . . . . . . . .57.2. Informative References . . . . . . . . . . . . . . . . .5 Author's Address . . . . . . . . . . . . . . . . . . . . . . . .51. Introduction The Constrained Application Protocol (CoAP) [RFC7252] provides a lightweight request-response messaging mechanism for retrieving and manipulating resources identified by Uniform Resource Identifiers (URIs). However URIs have a twofold purpose in CoAP: In addition to identifying resources, URIs are also used as locators for origin servers, proxies and endpoints delivering resource representations to clients. Should an origin server wish to serve a resource over multiple transports, a single CoAP URI cannot be used to express the identity of the resource independently of alternate underlying transports or protocol configurations. Similarly, if the server wishes to serve representations of the resource from a different endpoint and path, the URI mechanism is incapable of capturing the relationship between these alternate representations or locations. This draft proposes a new link format attribute as well as a new link relation type that together enable an origin server to serve a resource from other protocol configuratons or endpoints. CoAP clients then interact with an origin server's CoRE resource discovery interface to obtain a set of links describing alternate locations of resources. This is useful in the following cases: 1. CoAP clients interacting with Type T1 or T2 CoAP origin servers (see Section 3 of [I-D.silverajan-core-coap-alternative-transports]) either before or during an ongoing transaction to communicate using CoAP over a different protocol configuration or alternative transport. 2. Avoiding URI aliases [WWWArchv1], where a single resource is represented with multiple URIs, without describing relations among the alternate representations.Silverajan Expires September 10, 2015 [Page 2]
Internet-Draft CoAP Protocol Negotiation March 2015 3. Allowing intermediate nodes such as CoAP-based proxies to intelligently cache and respond to CoAP clients with the same resource representation requested over alternative transports or server endpoints. 4. Ability to separate the CoAP resource paths from web-based CoAP endpoint path in a URI.2. New Link Attribute and Relation types A CoAP server wishing to allow interactions with resources from multiple locations or transports can do so by specifying the Transport Type "tt" link attribute, which is an opaque string. Multiple transport types can be included in the value of this parameter, each separated by a space. In such cases, transport types appear in a prioritised list, with the most preferred transport type by the CoAP server specified first and the lowest priority transport type last. At the same time, each transport type supported by the server is also described with an "altloc" link relation type. The "altloc" relation type specifices a URI (containing the URI scheme, authority and optionally path) providing an alternate endpoint location up to but not including the resource path of a representation. Both "tt" and "altloc" are optional CoAP features. If supported, they occur at the granularity level of an origin server, ie. they cannot be applied selectively on some resources only. Therefore "altloc" is always anchored at the root resource ("/"). Additionally, the "tt" link attribute and "altloc" relation type can be ignored by unsupported CoAP clients. (TBD: As type T1 nodes may not have all transports active at all times, should a lifetime value be reflected in server responses?)3. Examples Example 1 shows a CoAP server returning all transport types and the alternate resource locations to a CoAP client performing a CoAP Request to ./well-known/core In this case, the server supplies two different locations to interact with resources using CoAP over TCP. At the same time, the path to the WebSocket endpoint is provided in addition to the FQDN of the server, for using CoAP over WebSockets.Silverajan Expires September 10, 2015 [Page 3]
Internet-Draft CoAP Protocol Negotiation March 2015 REQ: GET /.well-known/core RES: 2.05 Content </sensors>;ct=40;title="Sensor Index", tt="tcp ws sms", </sensors/temp>;rt="temperature-c";if="sensor", </sensors/light>;rt="light-lux";if="sensor", <coap+tcp://server.example.com/>;rel="altloc", <coap+tcp://server.example.net/>;rel="altloc", <coap+ws://server.example.com/ws-endpoint/>;rel="altloc", <coap+sms://001234567>;rel="altloc" Figure 1: Example of Server response Example 2 shows a CoAP client actively soliciting a CoAP server for all supported transport types and protocol configurations. REQ: GET /.well-known/core?tt=* RES: 2.05 Content </sensors>;tt="tcp sms ws" <coap+tcp://server.example.com/>;rel="altloc", <coap+tcp://server.example.net/>;rel="altloc", <coap+ws://server.example.com/ws-endpoint/>;rel="altloc", <coap+sms://001234567/>;rel="altloc" Figure 2: CoAP client discovering transports supported by a CoAP server. Example 3 shows a CoAP client explicitly soliciting support for a specific transport type using a query filter parameter. REQ: GET /.well-known/core?tt=sms RES: 2.05 Content </sensors>;tt="tcp sms ws" <coap+sms://001234567/>;rel="altloc" Figure 3: CoAP client looking for a specific transport to use with a CoAP server.Silverajan Expires September 10, 2015 [Page 4]
Internet-Draft CoAP Protocol Negotiation March 20154. IANA Considerations New link attributes and link relations need to be registered.5. Security Considerations Probably lots. (TBD)6. Acknowledgements Thanks to Klaus Hartke for comments and reviewing this draft, and Teemu Savolainen for initial discussions about protocol negotations and lifetime values.7. References7.1. Normative References [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained Application Protocol (CoAP)",RFC 7252, June 2014.7.2. Informative References [I-D.silverajan-core-coap-alternative-transports] Silverajan, B. and T. Savolainen, "CoAP Communication with Alternative Transports",draft-silverajan-core-coap-alternative-transports-07 (work in progress), December 2014. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels",BCP 14,RFC 2119, March 1997. [WWWArchv1]http://www.w3.org/TR/webarch/#uri-aliases, "Architecture of the World Wide Web, Volume One", December 2004.Author's Address Bilhanan Silverajan Tampere University of Technology Korkeakoulunkatu 10 FI-33720 Tampere Finland Email: bilhanan.silverajan@tut.fiSilverajan Expires September 10, 2015 [Page 5]
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