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Sleepy Devices in CoAP - Problem Statement

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This is an older version of an Internet-Draft whose latest revision state is "Expired".
Authors Akbar Rahman , Thomas Fossati , Salvatore Loreto , Matthieu Vial
Last updated 2012-10-15
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CORE WG                                                        A. Rahman
Internet-Draft                          InterDigital Communications, LLC
Intended status: Informational                                T. Fossati
Expires: April 18, 2013                                        KoanLogic
                                                               S. Loreto
                                                                 M. Vial
                                                        October 15, 2012

               Sleepy Devices in CoAP - Problem Statement


   This document analyzes the COAP protocol issues related to sleeping
   devices.  The only goal of this document is to trigger discussions in
   the CORE WG so that all relevant considerations for sleeping devices
   are taken into account when designing CoAP.

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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   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 April 18, 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
   ( in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect

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   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.  Terminology and Conventions . . . . . . . . . . . . . . . . . . 3
   2.  What is a Sleeping Device?  . . . . . . . . . . . . . . . . . . 4
     2.1.  Sleeping behaviors. . . . . . . . . . . . . . . . . . . . . 4
     2.2.  Different Sleep Modes . . . . . . . . . . . . . . . . . . . 5
       2.2.1.  Always-On . . . . . . . . . . . . . . . . . . . . . . . 5
       2.2.2.  Intermittent Presence . . . . . . . . . . . . . . . . . 5
   3.  Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . . 5
   4.  Objectives  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 6
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   7.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 7
     8.2.  Informative References  . . . . . . . . . . . . . . . . . . 7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 7

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1.  Terminology and Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

   This document assumes readers are familiar with the terms and
   concepts that are used in [I-D.ietf-core-coap],
   [I-D.ietf-core-link-format], [I-D.ietf-core-observe],

   In addition, this document defines the following terminology:

   Sleeping End Point (SEP):  is a special kind of CoAP enabled device
      that spends a large amount of its lifetime disconnected from the
      network, mainly to save power, or just because it is downright
      unable to store the energy required for its functioning.  It
      nonetheless owns and hosts a set of resources, and needs to make
      them available to the other participants in the same constrained
      RESTful environment.  In this respect it has to devise and
      implement the mechanisms that allows to work around its
      limitation, and let its resources be accessible as if it were an
      usual, always connected, CoAP server.

   Resource Delegation:  is the transfer of control over the handling of
      a resource from an endpoint (the owner) to another (the deputy),
      without the actual ownership being relinquished.

      The retention of ownership implies two things: first, that a
      genuine resource delegation cannot be recursive, and second, that
      it must always be entirely reversible, at any time the owning
      endpoint deems appropriate.

      A Resource Delegation mechanism may comprise the transfer of the
      following information from the owner to the deputy endpoint:
      (a)  complete or partial namespace,
      (b)  one or more representations of the resource,
      (c)  associated metadata,
      (d)  allowed methods,
      (e)  access control information,
      (f)  temporal bounds of the delegation.
      Said mechanism may also provide authentication to the parties
      involved in the delegation process.

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2.  What is a Sleeping Device?

   A Sleeping device is a device able to cut power to unneeded
   subsystems and so significantly reduce battery consumption.  Some
   Sleeping devices only cut power to the radio system while continuing
   to run normally the other ones.  Other Sleeping devices are even more
   energy efficient being able to save the machine state in the RAM
   memory, putting the RAM into a minimum power state, and cutting power
   to all the other subsystems.  Finally other Sleeping device are able
   to save the machine state on an hard disk and completely switching
   off themselves.

2.1.  Sleeping behaviors.

   In this section we discuss different behaviors and scenarios of
   sleeping nodes.  Such behaviors can affect the design of applications
   (such as CoAP) and network topologies (such as proxies and caching).

   Sleeping nodes can have various sleeping patterns.  Sleep patterns
   can be predictable or totally unpredictable.  For example, some nodes
   sleep at a fixed interval or upon certain triggers.  Some nodes may
   sleep at irregular time intervals, or switch to sleep mode
   spontaneously.  Some nodes stay in sleep mode and only wake up upon
   certain event triggers.  A network may thus not be well aware of the
   sleeping state of a node at a given time.

   The duration of sleeping mode also varies largely, possibly from a
   few seconds to days.  From the perspective of applications, it may
   not be affected by the sleeping period if it is very short.  For
   example, a HTTP/TCP connection may still work (even if sub-optimally)
   if the sleep cycle is much shorter than the TCP retransmission timer.
   In contrast, if the sleeping period of a node exceeds a certain
   threshold it can impact an application.  This threshold however, can
   be difficult to predict and often can vary from device to device and
   network to network.  For example, this threshold can be very
   dependent on the topology of a constrained network especially for the
   case where a multi-hop path consists of multiple sleeping nodes.  For
   this case, the cumulative effect of multiple sleeping nodes must be

   The network topology also affects how to handle sleeping nodes.  For
   example, in a star shaped network, a proxy node (assuming to be not a
   sleeping node) can cache for the sleeping nodes within the network in
   a centralized manner.  However, in a P2P or mesh network, especially
   when multi-hops are involved, caching can be difficult and delivering
   of messages can be largely delayed due to nodes' sleeping cycles.  In
   this case distributed proxying and caching at intermediate nodes
   within the network (rather than just a single node such as the border

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   node or sink) may make sense, if intermediate nodes are not sleeping
   nodes and have adequate resources to support caching.

2.2.  Different Sleep Modes

2.2.1.  Always-On

   Any sleep is so short that it is invisible to L3 and upper which
   gives the illusion of the sleepy node of being always on => usual
   Server Model can be efficiently used.

2.2.2.  Intermittent Presence

   Long and possibly non pre-determined sleep periods (more than 1 sec,
   but typically in the order of minutes or hours) => Server Model not
   working anymore.  SEP state must be handled by other mechanisms.

3.  Assumptions

   The characteristics of SEPs varies widely.  Some may be cheap,
   rudimentary widgets with very limited computational and storage
   capabilities; other can be more functional devices yet in need to
   save energy since they have to be in operation for a long period
   while battery powered.

   This great variance implies that a fair number of often contradictory
   assumptions must be taken into consideration, and carefully weighted,
   when designing a comprehensive solution for the problem.  For

   o  Is SEP able to maintain soft state ?

   o  Is SEP sleep/awake scheduling predictable ?


   Luckily, and by definition, it can be assumed that all the SEPs
   participating in a CoRE domain share a (realistically limited) subset
   of the REST principles.  At the very least we will assume a SEP
   understands and implements:

   o  the concept of information resource and its representational

   o  the semantics and syntax of URIs;

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   o  the semantics associated to the most basic methods (i.e.  GET,

   that will provide the common ground on which to build their
   integration into the hosting CoRE domain.

4.  Objectives

   The CORE WG aim is to design a solution that, leveraging on the
   existing CoAP features and its REST architecture, allows SEP devices
   to be easily and smoothly integrated within any CoRE domain together
   with the all the other CoAP enabled devices.

   The ideal solution should:

   o  Make the set of resource owned and hosted by any SEP available to
      all the other participants, in the same constrained RESTful
      environment, without making any assumption on the presence of
      specific or special entities neither on the network topology.

   o  Provide the possibility to use Client or Observer Model to access
      resources owned and hosted by a SEP.

   o  Allow the (Secure) delegation of resource handling while retaining

   o  Minimize the configuration needs to bootstrap a SEP within an
      existing CoRE domain.

   o  Maximize the integration with base CoRE Features (i.e.  Resource
      Discovery, Multicast, Observer, Block).

   o  Reuse already available CoAP mechanisms as much as possible.

5.  Acknowledgements


6.  IANA Considerations

   This memo includes no request to IANA.

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7.  Security Considerations

   TBD.  (All drafts are required to have a security considerations
   section.  See RFC 3552 [RFC3552] for a guide.)

8.  References

8.1.  Normative References

              Shelby, Z., Hartke, K., Bormann, C., and B. Frank,
              "Constrained Application Protocol (CoAP)",
              draft-ietf-core-coap-12 (work in progress), October 2012.

              Shelby, Z., "CoRE Link Format",
              draft-ietf-core-link-format-14 (work in progress),
              June 2012.

              Hartke, K., "Observing Resources in CoAP",
              draft-ietf-core-observe-06 (work in progress),
              September 2012.

              Shelby, Z., Krco, S., and C. Bormann, "CoRE Resource
              Directory", draft-shelby-core-resource-directory-04 (work
              in progress), July 2012.

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

8.2.  Informative References

   [RFC3552]  Rescorla, E. and B. Korver, "Guidelines for Writing RFC
              Text on Security Considerations", BCP 72, RFC 3552,
              July 2003.

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Authors' Addresses

   Akbar Rahman
   InterDigital Communications, LLC
   Montreal, Quebec  H3A 3G4

   Phone: +1-514-585-0761

   Thomas Fossati


   Salvatore Loreto
   Hirsalantie 11
   Jorvas  02420


   Matthieu Vial


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