[Docs] [txt|pdf] [Tracker] [Email] [Nits]

Versions: 00 01 02 03

Internet Engineering Task Force                               T. Fossati
Internet-Draft                                                 KoanLogic
Intended status: Standards Track                             P. Giacomin
Expires: January 10, 2013                                      Freelance
                                                               S. Loreto
                                                                Ericsson
                                                            July 9, 2012


                        Publish Option for CoAP
                  draft-fossati-core-publish-option-00

Abstract

   This memo defines the Publish Option for the Constrained Application
   Protocol (CoAP).

   The Publish Option is used by a sleepy node to temporarily delegate
   the authority of one of its resources to another, always on, node
   which is typically a proxy but doesn't need to be necessarily.

   The sleepy node is given a simple RESTful messaging protocol that
   enables the setup, renew and removal of the authority transfer.  The
   whole process is driven by the (sleepy) origin, which may actually
   never need to listen or to keep any state.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 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 at http://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 January 10, 2013.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




Fossati, et al.         Expires January 10, 2013                [Page 1]


Internet-Draft           Publish Option for CoAP               July 2012


   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.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
     1.1.  Requirements Language and Motivation  . . . . . . . . . . . 3
   2.  Publish Option  . . . . . . . . . . . . . . . . . . . . . . . . 3
     2.1.  Publishing a Resource . . . . . . . . . . . . . . . . . . . 4
     2.2.  Updating a Resource . . . . . . . . . . . . . . . . . . . . 5
     2.3.  Unpublishing a Resource . . . . . . . . . . . . . . . . . . 5
     2.4.  Value Format  . . . . . . . . . . . . . . . . . . . . . . . 6
     2.5.  Discovery . . . . . . . . . . . . . . . . . . . . . . . . . 6
       2.5.1.  Publishing the /.well-known/core Resource . . . . . . . 6
       2.5.2.  Resource Directory  . . . . . . . . . . . . . . . . . . 7
   3.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 7
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 8
     6.1.  Normative References  . . . . . . . . . . . . . . . . . . . 8
     6.2.  Informative References  . . . . . . . . . . . . . . . . . . 8
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 9





















Fossati, et al.         Expires January 10, 2013                [Page 2]


Internet-Draft           Publish Option for CoAP               July 2012


1.  Introduction

   The proposal described in this memo covers the following use case: a
   node N, which is sleeping most of the time, depends one or more
   resources hosted at another sleepy node M. In cases as such, the
   probability of an empty intersection between their respective wake
   periods is very high, making it hard for the two to synchronize.

   In this scenario, using the basic observe [I-D.ietf-core-observe]
   functionality is not enough, as it could lead to lost state updates
   in case N is offline while M pushes its notifications; further, the
   observation may never bootstrap since its initialization needs both
   client and origin awake at the same time.

   This memo introduces an extension to the Proxy caching functionality
   that give the Proxy an explicit mediation role in the sleepy-to-
   sleepy CoAP [I-D.ietf-core-coap] communication.

1.1.  Requirements Language and Motivation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   This specification makes use of the following terminology:

   Sleepy Device:  a sensor/actuator (usually battery operated) that
      powers down its radio beyond the normal radio duty cycle in order
      to save energy.

   and tries to provide an in-protocol solution for the requirement REQ3
   stated in [I-D.shelby-core-coap-req]:

       The ability to deal with sleeping nodes.  Devices may be
       powered down at any point in time but periodically "wake up"
       for brief periods of time.


2.  Publish Option

   +-----+----------+---------+--------+--------+---------+
   | No. | C/E      | Name    | Format | Length | Default |
   +-----+----------+---------+--------+--------+---------+
   |  YY | Critical | Publish | uint   | 1 B    | 0x2     |
   +-----+----------+---------+--------+--------+---------+

   The Publish Option enables the sleepy origin to temporarily (i.e. for
   a specified "lease" time) delegate the authority of one of its hosted



Fossati, et al.         Expires January 10, 2013                [Page 3]


Internet-Draft           Publish Option for CoAP               July 2012


   resources to a Proxy node that will start to behave as the origin for
   the Publish'ed resource.  This allows a sleepy sensor to use the
   Proxy as the rendezvous point for one-way sleepy to sleepy signaling.

2.1.  Publishing a Resource

   P         S
   |   PUT   | Proxy-URI: coap://sleepy.example.org/res
   |<--------+ Publish: 0110
   |    r    | Content-Type: text/plain
   |         | ETag: 0xabcd
   |         | Max-Age: 1200
   |         |
   |  2.01   |
   +-------->|
   |         |

                                 Figure 1

   The origin server publishes one of its hosted resources, specified by
   the enclosed Proxy-URI, by PUT'ing it to the Proxy with a Publish
   Option attached.  The Publish Option value specifies the CoAP methods
   that clients are allowed to use on the resource (see Section 2.4).

   The example in Figure 1 shows a delegation where the GET and PUT
   methods are allowed while POST and DELETE are explicitly prohibited,
   meaning that the resource can be read and updated by clients, but it
   can't be deleted nor created.

   The Proxy, which is voluntarily charged by the resource owner to act
   as the delegated origin for the "lease" time specified by Max-Age,
   replies with a 2.01 if the authority transfer has succeeded.  An
   exact duplicate of the submitted representation is created, and from
   now on it can be accessed using the original URI provided that
   clients go through the delegated Proxy.  If the Publish operation
   does not succeed, the origin transfer fails, and an appropriate
   response code is returned.

   An ETag MAY be supplied as a metadata to be included in responses
   involving the Publish'ed representation.  If no Max-Age is given, a
   default of 3600 seconds MUST be assumed.  The Max-Age value, either
   implicit or explicit, determines the lifetime of the origin
   delegation.  When the Max-Age value is elapsed, the Proxy MUST delete
   the Publish'ed resource value and fall back to its usual proxying
   function.

   The Publish Option is critical and MUST be present in the request
   only.  If the Proxy does not recognize it, a 4.02 (Bad Option) MUST



Fossati, et al.         Expires January 10, 2013                [Page 4]


Internet-Draft           Publish Option for CoAP               July 2012


   be returned to the client.  If the option value is not correctly
   formatted (see Section 2.4), a 4.00 (Bad Request) MUST be returned to
   the client.

   It is sufficient for any client wishing to access the resource to do
   so using the Proxy node that, following the Publish operation, will
   start behaving a the origin, satisfying requests on behalf of the
   sleeping node.

   The Proxy MUST save the identity of the resource Publish'er in order
   to distinguish "maintainance" operations such as update and explicit
   deletion, from "regular" access to the published resource by clients.

   An interesting outcome of this communication strategy is that the
   sleepy origin may really never need to listen on its radio interface.

2.2.  Updating a Resource

   P         S
   |   PUT   | Proxy-URI: coap://sleepy.example.org/res
   |<--------+ Publish: 0110
   |    r    | Content-Type: text/plain
   |         | ETag: 0xdcba
   |         | Max-Age: 1200
   |         |
   |  2.04   |
   +-------->|
   |         |

                                 Figure 2

   In order to update the delegated resource state, the sleepy node
   shall send the very same request to the Proxy, which in turn replies
   with a 2.04 (Changed) status code in case the update operation has
   succeeded, or an appropriate error code in case it fails.

2.3.  Unpublishing a Resource

   P          S
   |  DELETE  | Proxy-URI: coap://sleepy.example.org/res
   |<---------+ Publish: 0x0
   |          |
   |          |
   |   2.02   |
   +--------->|
   |          |

   The delegation of a given resource can be explicitly revoked by the



Fossati, et al.         Expires January 10, 2013                [Page 5]


Internet-Draft           Publish Option for CoAP               July 2012


   real origin at any time before the lease time expires, by issuing a
   DELETE request to the Proxy hosting the resource duplicate with a
   Publish Option with value 0x0.

   On successful deletion of the delegation a 2.02 (Deleted) response
   code is returned by the Proxy.

2.4.  Value Format

   0 1 2 3 4 5 6 7
   +-+-+-+-+-+-+-+-+
   |C R U D 0 0 0 0|
   +-+-+-+-+-+-+-+-+

   Each of the first 4 bits is a flag field indicating whether the
   associated CoAP method (respectively: POST, GET, PUT and DELETE) is
   allowed on the Publish'ed resource.  The remaining 4 bits are unused
   and MUST be set to 0.

   In case the value is missing, the default is assumed to be 0x2, i.e.
   the resource is read-only.

   An all-0 value is used to explicitly revoke the delegation (see
   Section 2.3.)

   If the delegated Proxy receives a request with a method that is not
   compatible with the supplied mask, it MUST respond with a 4.05
   (Method Not Allowed) response code.

2.5.  Discovery

2.5.1.  Publishing the /.well-known/core Resource

   The [I-D.ietf-core-link-format] has no explicit text about "well-
   known" discovery of devices through a Proxy, nor about the
   cacheability rules for such resource.  Even if it seems reasonable to
   assume that the /.well-known/core URI is both query-able and
   cacheable through a Proxy, on the contrary the situation is not very
   much so.

   In fact, since the "well-known" interface relies on the resource
   origin being implicitly defined by the source address of the UDP
   packet carrying the response, quering the "well-known" interface
   (either unicast or multicast) through a Proxy-URI has little hope to
   be fully functional.  The (ab)use of a an implicit L3 locator as the
   identifier of the resource authority makes "well-known" discovery
   generally incompatible with Proxy mediated communication, unless each
   target URI in a link is given as a URI and not as a relative-ref



Fossati, et al.         Expires January 10, 2013                [Page 6]


Internet-Draft           Publish Option for CoAP               July 2012


   (section 4.1 of [RFC3986]).

   Consequently, in this proposal we assume that the /.well-known/core
   of a sleepy node can be Publish'ed if and only if the target URI in
   the each link is not a relative-ref.

   Its registration is the same as in Figure 1, but the Proxy MAY need
   to treat it in a way that is slightly different from other "normal"
   delegated resources.  In fact, while delegation is in place (i.e. the
   lease period is not elapsed, and neither explicit revocation has
   happened) the Proxy MAY be able to respond to filtered queries
   (section 4.1 of [I-D.ietf-core-link-format]) regarding the Publish'ed
   /.well-known/core.

2.5.2.  Resource Directory

   Given the strong requirement on the link formatting given in
   Section 2.5.1, it could be preferable (or even necessary) to use the
   Resource Directory [I-D.shelby-core-resource-directory] as a means of
   delegating the discovery of the resources hosted at a sleepy node.

   This can be done either by the sleepy node, or automatically by the
   delegated Proxy when a Publish request is received.

   [[Automatic push to RD: check it out]]


3.  Acknowledgements

   Bruce Nordman and Matthieu Vial for discussing and giving advice on
   some of the ideas contained in this document.


4.  IANA Considerations

   The following entries are added to the CoAP Option Numbers registry:

   .------------------------------.
   | Number | Name    | Reference |
   :--------:---------:-----------:
   |  2n+1  | Publish | RFC XXXX  |
   `------------------------------'


5.  Security Considerations






Fossati, et al.         Expires January 10, 2013                [Page 7]


Internet-Draft           Publish Option for CoAP               July 2012


   Threat:  cache poisoning.
   Countermeasure:  authenticate sender.

   Threat:  unauthorized de-registration
   Countermeasure:  authenticate requester.

   Threat:  Proxy resources' exhaustion.
   Countermeasure:  authenticate requester + quota limit.

   Threat:  global state loss.
   Countermeasure:  cache redundancy.


6.  References

6.1.  Normative References

   [I-D.ietf-core-coap]
              Frank, B., Bormann, C., Hartke, K., and Z. Shelby,
              "Constrained Application Protocol (CoAP)",
              draft-ietf-core-coap-08 (work in progress), October 2011.

   [I-D.ietf-core-link-format]
              Shelby, Z., "CoRE Link Format",
              draft-ietf-core-link-format-11 (work in progress),
              January 2012.

   [I-D.ietf-core-observe]
              Hartke, K., "Observing Resources in CoAP",
              draft-ietf-core-observe-04 (work in progress),
              February 2012.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, January 2005.

6.2.  Informative References

   [I-D.shelby-core-coap-req]
              Shelby, Z., Stuber, M., Sturek, D., Frank, B., and R.
              Kelsey, "CoAP Requirements and Features",
              draft-shelby-core-coap-req-02 (work in progress),
              October 2010.

   [I-D.shelby-core-resource-directory]



Fossati, et al.         Expires January 10, 2013                [Page 8]


Internet-Draft           Publish Option for CoAP               July 2012


              Krco, S. and Z. Shelby, "CoRE Resource Directory",
              draft-shelby-core-resource-directory-02 (work in
              progress), October 2011.


Authors' Addresses

   Thomas Fossati
   KoanLogic
   Via di Sabbiuno, 11/5
   Bologna  40100
   Italy

   Email: tho@koanlogic.com


   Pierpaolo Giacomin
   Freelance

   Email: yrz@anche.no


   Salvatore Loreto
   Ericsson
   Hirsalantie 11
   Jorvas  02420
   Finland

   Email: salvatore.loreto@ericsson.com






















Fossati, et al.         Expires January 10, 2013                [Page 9]


Html markup produced by rfcmarkup 1.129c, available from https://tools.ietf.org/tools/rfcmarkup/