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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


                        Monitor Option for CoAP
                  draft-fossati-core-monitor-option-00

Abstract

   This memo defines Monitor, an additional Option for the Constrained
   Application Protocol (CoAP) especially targeted at sleepy sensors.

   The Monitor Option complements the typical Observe pattern, enabling
   the tracking of a resource hosted by a node sleeping most of the
   time, by taking care of establishing and maintaining an Observe
   relationship with the (sleepy) origin on behalf of the (sleepy)
   client.

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
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   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
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   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.

   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



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   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.  Monitor Option  . . . . . . . . . . . . . . . . . . . . . . . . 3
     2.1.  Public Monitor Registration . . . . . . . . . . . . . . . . 4
     2.2.  Monitor De-registration . . . . . . . . . . . . . . . . . . 6
       2.2.1.  Explicit De-registration  . . . . . . . . . . . . . . . 6
       2.2.2.  Implicit De-registration  . . . . . . . . . . . . . . . 6
     2.3.  Resource Refresh  . . . . . . . . . . . . . . . . . . . . . 6
   3.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 7
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   6.  Normative References  . . . . . . . . . . . . . . . . . . . . . 7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 8




























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1.  Introduction

   The proposal described in this memo covers the following use case: a
   node N, which is sleeping most of the time, depends on 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 requirement REQ3 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.  Monitor Option

       +-----+----------+---------+--------+--------+---------+
       | No. | C/E      | Name    | Format | Length | Default |
       +-----+----------+---------+--------+--------+---------+
       |  XX | Critical | Monitor | (none) | 0 B    | (none)  |
       +-----+----------+---------+--------+--------+---------+

   The Monitor Option is a variant of the Observe Option that is aimed
   at solving some issues that may occur when sleepy sensors are



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   involved.

   Suppose that the resource of interest is not cached anywhere, and a
   sleepy endpoint wants to Observe it through a Proxy.  If the origin
   of the requested resource is sleeping at the time the observation is
   requested, the requesting node gets an error, and may need to stay
   awake and retry until the target node gets ready -- which is clearly
   not an option in case the sensor has a very small duty cycle.

   The Monitor Option is used to ask a Proxy to keep a given resource
   fresh by observing it, while the requesting node is sleeping.  Thus
   the sleepy sensor can possibly get the latest representation
   published by the monitored resource when it wakes up, even if the
   origin is sleeping -- and was sleeping at the time the Monitor has
   been requested.

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

2.1.  Public Monitor Registration

   P        C
   |  POST  | Proxy-URI: coap://sleepy.example.org/res
   |<-------+ Monitor: <empty>
   |        | Max-Age: 86400
   |        | Content-Type: application/json
   |  2.01  |
   +------->| Location-Path: temp
   |        | Location-Path: res
   |        |

                                 Figure 1

   The client POST's the resource to be monitored, identified by the
   Proxy-URI.  The request message contains an empty Monitor Option, and
   possibly specifies a TTL (i.e. an implicit de-registration
   indication) for the monitor through Max-Age.  One or more content
   types for the acceptable representations of the resource are
   optionally specified via the Accept option.  In case no TTL is
   supplied, a default value of 3600 seconds is assumed.

   The operation creates a "monitor" resource at the Proxy, that MUST
   maintain a fresh carbon copy of one or more representations of the
   requested resource depending on the supplied Content-Type.  For
   convenience, multiple "monitor" resources corresponding to the same
   target resource, can be coalesced into the same monitor object at the
   Proxy -- possibly with the same URI.  In such case, a set containing



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   one entry for each registered client is kept, which holds the client
   identities, their expiry and one or more preferred media types for
   their representation(s).  When all entries are deleted (either
   because clients have explicitly deregistered the monitor, or the
   monitor period has expired), the corresponding "monitor" object is
   deleted.  Note that an underlying cache entry MAY still be kept in
   case the cached representation(s) are still fresh (i.e. the Max-Age
   of the "monitor" resource and Max-Age of the target resource have
   completely different semantics.)

   If the monitor resource is successfully created, the server MUST
   return a 2.01 response containing one or more Location-Path and/or
   Location-Query Options to identify the monitored resource instance,
   which can be used from now on by the requester as an alias to the
   target resource.

   At a later time, the client wakes up and wants to access the
   monitored resource.  It does so by requesting the Proxy monitor
   resource that has been previously created.

   P        C
   |   GET  | URI-Path: temp
   |<-------+ URI-Path: res
   |        | Accept: application/json
   |        |
   |  2.05  |
   +------->| (Content)
   |        |
   |        |

                                 Figure 2

   In case the observation on the target node has not been started
   because the Proxy has not yet been able to contact the origin, the
   Proxy will return a [TBD] error code.

   In case the requested resource was not present on the origin, the
   Proxy will return an empty response (i.e. one with no payload.)

   [[XXX: add an explicit response code perhaps like HTTP 204 ?]]

   In case the monitor resource is not found in the Proxy, either
   because the Proxy has rebooted and lost its state, or the monitor
   resource has been de-registered (see Section 2.2), a 4.04 response
   code is returned to the client -- that can recreate it, if needed.






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2.2.  Monitor De-registration

   The monitor object MUST be deleted at the Proxy when all its
   associated resources have been de-registered or have expired.

   In order to save storage, a Proxy MAY decide to delete a monitor
   resource in case it has not been requested for a sufficiently long
   time, or for any other reason.  Note that the Proxy may also reboot
   and lose its state, including the state associated to any monitored
   resource.  The requester can realize that the state at the Proxy has
   been lost, and re-instantiate the monitor, when it receives an
   unexpected 4.04 from the "monitor" resource.

2.2.1.  Explicit De-registration

   P        C
   | DELETE | Path: temp
   |<-------+ Path: res
   |        |
   |  2.02  |
   +------->|
   |        |

                                 Figure 3

   Explicit de-registration is performed by a client, with a DELETE on
   the URI returned by the Proxy on the corresponding registration.

2.2.2.  Implicit De-registration

   Implicit de-registration MUST occur when the monitoring period
   specified by the client via Max-Age expires.  If no Max-Age was
   supplied at registration time, a default of 3600 seconds MUST be
   assumed.

2.3.  Resource Refresh

   In order to minimize the number of messages used by the monitoring
   process, the Proxy MUST try to install an observation on the
   requested resource.  In case this first attempt fails, the Proxy MAY
   fall back to repeated poll whose duration is upper bounded by the
   Max-Age value indicated by the client during registration.

   Usual cache validation MUST be applied to the cached copy of the
   monitored resource.






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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 |
   :--------:---------:-----------:
   |  2m+1  | Monitor | RFC XXXX  |
   `------------------------------'


5.  Security Considerations

   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.

   Threat:  DoS on remote constrained resource via unneeded monitoring.
   Countermeasure:  access control on the constrained resource (?)


6.  Normative References

   [I-D.ietf-core-coap]
              Shelby, Z., Hartke, K., Bormann, C., and B. Frank,
              "Constrained Application Protocol (CoAP)",
              draft-ietf-core-coap-10 (work in progress), June 2012.

   [I-D.ietf-core-observe]
              Hartke, K., "Observing Resources in CoAP",
              draft-ietf-core-observe-05 (work in progress), March 2012.

   [I-D.shelby-core-coap-req]
              Shelby, Z., Stuber, M., Sturek, D., Frank, B., and R.



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              Kelsey, "CoAP Requirements and Features",
              draft-shelby-core-coap-req-04 (work in progress),
              May 2011.

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


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



















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