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core                                                               K. Li
Internet-Draft                                       Huawei Technologies
Intended status: BCP                                    October 21, 2011
Expires: April 23, 2012


                             CoAP Over SMS
                     draft-li-core-coap-over-sms-00

Abstract

   This document explains how to use CoAP in cellular networks, by using
   SMS (Short Message Service) as the transport protocol.

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 April 23, 2012.

Copyright Notice

   Copyright (c) 2011 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
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.






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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
     1.1.  Motivation  . . . . . . . . . . . . . . . . . . . . . . . . 3
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  CoAP Over SMS . . . . . . . . . . . . . . . . . . . . . . . . . 3
     2.1.  Addressing  . . . . . . . . . . . . . . . . . . . . . . . . 3
     2.2.  Mapping to SMS Messages . . . . . . . . . . . . . . . . . . 4
     2.3.  Parameters Mapping  . . . . . . . . . . . . . . . . . . . . 5
     2.4.  Interaction with the Block option . . . . . . . . . . . . . 5
   3.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 5
   6.  Normative References  . . . . . . . . . . . . . . . . . . . . . 5
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 6




































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1.  Introduction

   In cellular networks, it is possible that constrained end-points
   don't support an IP stack, i.e.  TCP or UDP, but support the SMS
   protocol instead.  Compared to the UDP protocol stack, SMS provides a
   much smaller message size: SMS can transfer up to 140 bytes in each
   message.  So, some optimizations need to be done to reduce the CoAP
   message size to make it fit for SMS.  Also, some adaptations in CoAP
   need to be specified, to cater for SMS specific parameters.

1.1.  Motivation

   In some environments, internet connectivity is not supported by the
   constrained end-points, but a cellular network connection is
   supported instead.  In this situation, SMS will be supported, instead
   of UDP.

   In OMA, there is a new approved work item named "the Lightweight M2M
   Protocol", which aims at identifying requirements and defining
   protocols for M2M applications in cellular networks.

   In 3GPP, SMS is identified as the transport protocol for small data
   transmissions (See 3GPP-23.888).

   Currently, there are already some SMS based deployments for binary
   M2M protocols, which are quite similar to CoAP.

1.2.  Terminology

   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.  CoAP Over SMS

2.1.  Addressing

   In cellular networks, the CoAP endpoints have to work with a SIM
   (Subscriber Identity Module) card and have to be addressed by the
   MSISDN (Mobile Station ISDN (MSISDN) number).

   To allow the CoAP client to detect that the SMS message contains a
   CoAP message, the TP-DATA-Coding-Scheme SHOULD be included.







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2.2.  Mapping to SMS Messages

   When using SMS, the CoAP Client works as a Mobile Station to send the
   SMS message, and the CoAP Server works as another Mobile Station to
   receive the SMS message.  All the SMS messages are stored and
   forwarded by the Service Center.  The message exchange between the
   CoAP Client and the CoAP Server is depicted in the figure below:

    MS/CoAP CLIENT        Service Center          MS/CoAP SERVER
        |                       |                        |
        |   ---SMS-SUBMIT--->   |                        |
        | <-SMS-SUBMIT-REPORT-- |                        |
        |                       |                        |
        |                       |    --SMS-DELIVER--->   |
        |                       | <-SMS-DELIVER-REPORT-- |
        |                       |                        |
        | <-SMS-STATUS-REPORT-- |                        |
        |                       |                        |

                    Figure 1: CoAP Messages over SMS

   Note that the message exchange is just for one request message from
   CoAP Client and CoAP Server.  It includes the following steps:

   Step 1: The CoAP Client sends a CoAP request in a SMS-SUBMIT message
   to the Service Center.  The CoAP Server address is specified as TP-
   Destination-Address (see see 3GPP-23.040).

   Step 2: The Service Center returns a SMS-SUBMIT-REPORT message to the
   CoAP Client.

   Step 3: The Service Center stores the received SMS message and
   forwards it to the CoAP Server, using an SMS-DELIVER message.  The
   CoAP Client address is specified as a TP Originating Address (see
   3GPP-23.040).

   Step 4: The CoAP Server returns an SMS-DELIVER-REPORT message to the
   Service Center.

   Step 5: The Service Center returns the SMS-STATUS-REPORT message to
   the CoAP Client to indicate the SMS delivery status, if required by
   the CoAP Client.

   Note that the SMS-STATUS-REPORT message just indicates the transport
   layer SMS delivery status and has no relationship with the
   confirmable message or non-confirmable message.  If the CoAP Client
   has sent a confirmable message, the CoAP Server MUST use a separate
   SMS message to transmit the ACK.



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2.3.  Parameters Mapping

   In case of SMS transport, MSISDN MUST be used as the value of the
   Uri-Host option.  The Uri-Port option SHOULD not be sent, as it is
   not used for SMS transport.

2.4.  Interaction with the Block option

   It is RECOMMENDED that SMS is not used to transfer very large
   resource data using Blocks.


3.  Security Considerations

   Security mechanisms defined in 3GPP-23.888 are used to guarantee
   transport security.

   It is possible that a malicious CoAP Client sends repeated requests,
   and it may cost money for the CoAP Server to use SMS to send back
   associated responses.  To avoid this situation, the CoAP Server
   implementation can authenticate the CoAP Client before responding to
   the requests.  For example, the CoAP Server can maintain a MSISDN
   white list.  Only the MSISDN specified in the white list will be
   allowed to send requests.  The requests from others will be ignored
   or rejected.


4.  IANA Considerations

   N/A.


5.  Acknowledgements

   The authors of this draft would like to thank Bert Greevenbosch for
   the discussion.


6.  Normative References

   [I-D.ietf-core-block]
              Bormann, C. and Z. Shelby, "Blockwise transfers in CoAP",
              draft-ietf-core-block-04 (work in progress), July 2011.

   [I-D.ietf-core-coap]
              Shelby, Z., Hartke, K., Bormann, C., and B. Frank,
              "Constrained Application Protocol (CoAP)",
              draft-ietf-core-coap-07 (work in progress), July 2011.



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


Author's Address

   Kepeng Li
   Huawei Technologies
   Huawei Base, Bantian, Longgang District
   Shenzhen, Guangdong  518129
   P. R. China

   Phone: +86-755-28974289
   Email: likepeng@huawei.com





































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