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CoRE Working Group                                        M. Becker, Ed.
Internet-Draft                                            K. Kuladinithi
Intended status: Informational                                T. Poetsch
Expires: April 26, 2012                  ComNets, TZI, University Bremen
                                                        October 24, 2011


                  Transport of CoAP over SMS and GPRS
                   draft-becker-core-coap-sms-gprs-00

Abstract

   The Short Message Service (SMS) of mobile cellular networks is
   frequently used in Machine-To-Machine (M2M) communications, such as
   for telematic devices.  The service offers small packet sizes and
   high delays just as other typical low-power and lossy networks
   (LLNs), i.e. 6LoWPANs.  The design of the Constrained Application
   Protocol (CoAP), that took the limitations of LLNs into account, is
   thus also applicable to telematic M2M devices.  The adaption of CoAP
   to the SMS transport mechanism is described in this document.

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 26, 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
   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



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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.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
     1.1.  Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . 3
     1.2.  Requirements Language . . . . . . . . . . . . . . . . . . . 5
   2.  Encoding of CoAP for SMS transport  . . . . . . . . . . . . . . 5
   3.  Message Size Implementation Considerations  . . . . . . . . . . 5
   4.  Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
   5.  Protocol Constants  . . . . . . . . . . . . . . . . . . . . . . 6
   6.  Multicast . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
   7.  Proxying Considerations . . . . . . . . . . . . . . . . . . . . 6
   8.  SMS URI scheme for link-format  . . . . . . . . . . . . . . . . 6
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 6
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
   11. Security Considerations . . . . . . . . . . . . . . . . . . . . 6
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . . . 7
     12.1. Normative References  . . . . . . . . . . . . . . . . . . . 7
     12.2. Informative References  . . . . . . . . . . . . . . . . . . 7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 7


























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1.  Introduction

   This specification details the usage of the Constrained Application
   Protocol on the Short Message Service of mobile cellular networks.

1.1.  Scenarios

   Figure 1 to Figure 5 show various applicable usage scenarios of CoAP
   in M2M communications.  Two mobile cellular terminals communicate by
   exchanging CoAP Request and Response embedded into SMS PDUs (depicted
   in Figure 1).

                                  CoAP-REQ
                         +------+  (SMS)   +------+
                         |  A   | -------> |  B   |
                         |(cell)| <------- |(cell)|
                         +------+ CoAP-RES +------+
                                   (SMS)

      Figure 1: Cellular and Cellular Communication (only SMS-based)

   Two mobile cellular terminals communicate by exchanging the CoAP
   Request in an SMS PDU and the CoAP Responce using GPRS transport.
   (depicted in Figure 2).

                                  CoAP-REQ
                         +------+  (SMS)   +------+
                         |  A   | -------> |  B   |
                         |(cell)| <------- |(cell)|
                         +------+ CoAP-RES +------+
                                   (GPRS)

      Figure 2: Cellular and Cellular Communication (SMS/GPRS-based)

   An IP host and a mobile cellular terminal communicate by exchanging
   CoAP Request and Response.  The IP host uses protocols offered by the
   SMS-C (e.g.  Computer Interface to Message Distribution (CIMD
   [cimd]), Universal Computer Protocol/External Machine Interface (UCP/
   EMI [ucp]), Short Message Peer-to-Peer (SMPP [smpp]) ) to submit an
   SMS for delivery, which contains the CoAP Request (depicted in
   Figure 3).










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                          CIMD
                         UCP/EMI            CoAP-REQ
               +------+   SMPP    +-------+   (SMS)  +------+
               |  A   | --------> | SMS-C | -------> |  B   |
               | (IP) | <-------- |       | <------- |(cell)|
               +------+           +-------+ CoAP-RES +------+
                                              (SMS)

         Figure 3: IP and Cellular Communication (only SMS-based)

   Again, the return path for the CoAP response might be GPRS (depicted
   in Figure 4).

                          CIMD
                         UCP/EMI            CoAP-REQ
               +------+   SMPP    +-------+   (SMS)  +------+
               |  A   | --------> | SMS-C | -------> |  B   |
               | (IP) |           |       |          |(cell)|
               +------+           +-------+          +------+
                  ^                                     |
                  |               +-------+             |
                  |               | GGSN  |             |
                  +-------------- |       | <-----------+
                                  +-------+    CoAP-RES
                                               (GPRS)

         Figure 4: IP and Cellular Communication (SMS/GPRS-based)

   There are service providers offering SMS delivery and notification
   using an HTTP/REST interface (depicted in Figure 5).

                                        CIMD
              HTTP-REQ                 UCP/EMI         CoAP-REQ
    +------+ (CoAP-DATA) +-----------+  SMPP   +-----+   (SMS)  +------+
    |  A   | ----------> |SMS Service| ------> |SMS-C| -------> |  B   |
    | (IP) | <---------- |Provider   | <------ |     | <------- |(cell)|
    +------+  HTTP-RES   +-----------+         +-----+ CoAP-RES +------+
             (CoAP-DATA)                                 (SMS)

   Figure 5: IP and Cellular Communication (only SMS-based, using an SMS
                             service provider)

   At the moment, this document assumes the scenarios shown in Figure 1,
   Figure 3 and Figure 5), i.e.\ only SMS transport.







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1.2.  Requirements Language

   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 RFC 2119 [RFC2119].


2.  Encoding of CoAP for SMS transport

   The content of SMS can be coded in 7, 8 or 16 bit characters
   [3gpp_ts23.038].  The advantages and disadvantages are:

   a.  7 bit encoding: Sending 7 bit encoded SMS possible with almost
       all devices.  CoAP binary data needs to be re-encoded, possibly
       with Base64 RFC 4648 [RFC4648].

   b.  8 bit encoding: CoAP binary data does not need to be re-encoded.
       Not all telematic devices support 8 bit SMS encoding.

   c.  16 bit encoding: CoAP binary data needs to be re-encoded.  Not
       all telematic devices support 16 bit SMS encoding.

   The currently safest solution is to use 7 bit encoded SMS including
   Base64 encoded CoAP payload.


3.  Message Size Implementation Considerations

   Using 7 bit encoding 160 characters are allowed in 1 SMS, while using
   8 bit encoding 140 characters are allowed.  [3gpp_ts23.038]

   Possible options for larger CoAP messages are:

   a.  Multiple SMS concatenation

   b.  CoAP Block [I-D.ietf-core-block]


4.  Options

   Uri-Host and Uri-Port options MUST NOT be included in the CoAP
   header.  End-points receiving CoAP messages over SMS with such
   options MUST behave as specified in [I-D.ietf-core-coap].

   Open question: Is the introduction of a new CoAP option Reply-To-Uri-
   Host necessary, if the server should use the GPRS transport for the
   Response?  This relates to Figure 2 and Figure 4.




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   +--------+----------+-------------------+--------+--------+---------+
   | Number |    C/E   |        Name       | Format | Length | Default |
   +--------+----------+-------------------+--------+--------+---------+
   |   17   | Critical | Reply-To-Uri-Host | string |  1-270 |  (none) |
   |        |          |                   |        |    B   |         |
   |   19   | Critical | Reply-To-Uri-Port |  uint  |  0-2 B |  (none) |
   +--------+----------+-------------------+--------+--------+---------+

                     Table 1: New CoAP Option Numbers


5.  Protocol Constants

   The RESPONSE_TIMEOUT variable SHOULD be configured for a higher
   duration than specified in [I-D.ietf-core-coap], i.e. 10 s.


6.  Multicast

   Multicast MUST not be used with the SMS transport.


7.  Proxying Considerations

   TBD (Proxying into an IPv6/v4 network (e.g. a 6LoWPAN network)
   possible?)


8.  SMS URI scheme for link-format

   Open question: Make use of RFC5724 SMS URI scheme?


9.  Acknowledgements

   This document is based on research for the research project 'The
   Intelligent Container' which is supported by the Federal Ministry of
   Education and Research, Germany, under reference number 01IA10001.


10.  IANA Considerations

   This memo includes no request to IANA.


11.  Security Considerations

   This presents no security considerations beyond those in section 10



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   of the base CoAP specification [I-D.ietf-core-coap].


12.  References

12.1.  Normative References

   [3gpp_ts23.038]
              ETSI 3GPP, "Technical Specification: Alphabets and
              language-specific information (3GPP TS 23.038 version
              10.0.0 Release 10)", 2011.

   [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.

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

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, October 2006.

12.2.  Informative References

   [cimd]     Nokia, "CIMD Interface Specification (SMSCDOC8000.00,
              Nokia SMS Center 8.0)", 2005.

   [smpp]     SMPP Developers Forum, "Short Message Peer to Peer
              Protocol Specification v3.4 Issue 1.2", 1999.

   [ucp]      Vodafone, "Short Message Service Centre (SMSC) External
              Machine Interface (EMI) Description Version 4.3d", 2011.














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Authors' Addresses

   Markus Becker (editor)
   ComNets, TZI, University Bremen
   Bibliothekstrasse 1
   Bremen  28359
   Germany

   Phone: +49 421 218 62379
   Email: mab@comnets.uni-bremen.de


   Koojana Kuladinithi
   ComNets, TZI, University Bremen
   Bibliothekstrasse 1
   Bremen  28359
   Germany

   Phone: +49 421 218 62382
   Email: koo@comnets.uni-bremen.de


   Thomas Poetsch
   ComNets, TZI, University Bremen
   Bibliothekstrasse 1
   Bremen  28359
   Germany

   Phone: +49 421 218 62379
   Email: thp@comnets.uni-bremen.de





















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