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CoRE Working Group                                         A. Castellani
Internet-Draft                                      University of Padova
Intended status: Standards Track                               S. Loreto
Expires: September 30, 2012                                     Ericsson
                                                          March 29, 2012


                           CoAP Alive Message
                     draft-castellani-core-alive-00

Abstract

   In the context of a Constrained RESTful Environment (CoRE), hosts
   could frequently be energy-constrained and be turned off the vast
   majority of time for energy-saving purposes.

   In the case of a CoAP server, while it is offline, it is neither
   available to serve requests.  Clients desiring to access its
   resources have no way to understand when they will find it up again.

   This specification provides a simple new message that gives to a CoAP
   server the ability to signal its current availability in the network.

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 September 30, 2012.

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
   2.  Alive (ALV) Message Type  . . . . . . . . . . . . . . . . . . . 3
   3.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   4.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 6
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 6
     5.1.  Normative References  . . . . . . . . . . . . . . . . . . . 6
     5.2.  Informative References  . . . . . . . . . . . . . . . . . . 6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 6

































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1.  Introduction

   In the context of a Constrained RESTful Environment (CoRE), hosts
   could frequently be energy-constrained and be turned off the vast
   majority of time for energy-saving purposes.

   In the case of a CoAP server, while it is offline, it is neither
   available to serve requests.  Clients desiring to access its
   resources have no way to understand when they will find it up again.

   This specification provides a simple new message that gives to a CoAP
   server the ability to signal its current availability in the network.

   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].


2.  Alive (ALV) Message Type

   This specification defines a new message type for the CoAP message-
   layer (see Section 4.4 of [I-D.ietf-core-coap]).  The type of a
   message is specified by the T field of the CoAP header.

   An "Alive" message (ALV) indicates that a CoAP server is up and ready
   to serve requests.  Alive shares T value with the Non-Confirmable
   (NON) message type, but is univocally distinguishable by the fact
   that it MUST be empty.

   When a client receives an ALV message from a server, if it is
   interested in any resource served by it, the client SHOULD try
   sending a request to it since the Alive message provides an
   indication of its current availability.


3.  Examples

   Figure 1 shows a sample use case where a server notifies its wake up
   to clients using multicast.












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   C1  C2  C3    S
   |   |   |     . server is sleeping
   |   |   |     .
   |   |   |     .
   |   |   |     .
   |   |   |     . server wakes up
   |<--|<--|<----| ALV MID=0xfefe
   |   |   |     |
   |   |   |     | CON MID=0x1234
   |------------>| GET /a
   |   |   |     |
   |   |   |     | ACK MID=0x1234
   |<------------| 2.05 "A"
   |   |   |     .
   |   |   |     . server goes sleeping again
   |   |   |     .
   |   |   |     .
   |   |   |     .


                       Figure 1: Alive usage example

   Figure 2 shows a sample application on how the Alive message can fix
   the "Observer Model" problem discussed in Section 4.2.3 of
   [I-D.arkko-core-sleepy-sensors].


























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   C1  C2  C3    P    S
   |   |   |     |    . server is sleeping
   |   |   |     |    .
   |   |   |     |    . CON MID=0x1234
   |   |   |     |    . GET
   |   |   |     |    . Proxy-URI: coap://S/temp
   |------------>|    . Observe: 0
   |   |   |     |    .
   |<------------|    . ACK MID=0x1234
   |   |   |     |    .
   |   |   |     |    . (time passes..)
   |   |   |     |    .
   |   |   |     |    . server wakes up
   |   |   |     |<---| ALV MID=0xfefe
   |   |   |     |    |
   |   |   |     |    | CON MID=0xabcd
   |   |   |     |    | GET /temp
   |   |   |     |--->| Observe:0
   |   |   |     |    |
   |   |   |     |    | ACK MID=0xabcd
   |   |   |     |    | 2.05 "22.5 C"
   |   |   |     |<---| Observe: 789
   |   |   |     |    .
   |   |   |     |    . CON MID=0xabce
   |   |   |     |    . 2.05 "22.5 C"
   |<------------|    . Observe: 3013
   |   |   |     |    .
   |------------>|    . ACK MID=0xabce
   |   |   |     |    .
   |   |   |     |    . (time passess..)
   |   |   |     |    .
   |   |   |     |    . resource state changes
   |   |   |     |    . NON MID=0xfeff
   |   |   |     |    . 2.05 "21.5 C"
   |   |   |     |<---| Observe: 1384
   |   |   |     |    .
   |   |   |     |    .
   |   |   |     |    . NON MID=0xabcf
   |   |   |     |    . 2.05 "22.5 C"
   |<------------|    . Observe: 3013
   ...


                       Figure 2: Alive with Observe







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4.  Acknowledgements

   TBD


5.  References

5.1.  Normative References

   [I-D.ietf-core-coap]
              Shelby, Z., Hartke, K., Bormann, C., and B. Frank,
              "Constrained Application Protocol (CoAP)",
              draft-ietf-core-coap-09 (work in progress), March 2012.

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

5.2.  Informative References

   [I-D.arkko-core-sleepy-sensors]
              Arkko, J., Rissanen, H., Loreto, S., Turanyi, Z., and O.
              Novo, "Implementing Tiny COAP Sensors",
              draft-arkko-core-sleepy-sensors-00 (work in progress),
              July 2011.


Authors' Addresses

   Angelo P. Castellani
   University of Padova
   Via Gradenigo 6/B
   Padova  35131
   Italy

   Email: angelo@castellani.net


   Salvatore Loreto
   Ericsson
   Hirsalantie 11
   Jorvas  02420
   Finland

   Email: salvatore.loreto@ericsson.com







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