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CoRE Working Group                                        M. Becker, Ed.
Internet-Draft                           ComNets, TZI, University Bremen
Intended status: Informational                                     K. Li
Expires: September 2, 2012                           Huawei Technologies
                                                          K. Kuladinithi
                                                              T. Poetsch
                                         ComNets, TZI, University Bremen
                                                           March 1, 2012


               Transport of CoAP over SMS, USSD and GPRS
                   draft-becker-core-coap-sms-gprs-01

Abstract

   The Short Message Service (SMS) and Unstructured Supplementary
   Service Data (USSD) 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 adaptation of CoAP to the SMS or USSD
   transport mechanisms and the combination with IP transported over
   cellular networks 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
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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 September 2, 2012.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




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   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
   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.  Motivation . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  4
   3.  Requirements Language  . . . . . . . . . . . . . . . . . . . .  4
   4.  Scenarios  . . . . . . . . . . . . . . . . . . . . . . . . . .  4
     4.1.  MO-MT Scenarios  . . . . . . . . . . . . . . . . . . . . .  4
     4.2.  MT Scenarios . . . . . . . . . . . . . . . . . . . . . . .  5
     4.3.  MO Scenarios . . . . . . . . . . . . . . . . . . . . . . .  6
   5.  Message Exchanges  . . . . . . . . . . . . . . . . . . . . . .  7
     5.1.  Message Exchange for SMS in a Cellular-To-Cellular
           Mobile-Originated and Mobile-Terminated Scenario . . . . .  7
     5.2.  Message Exchange for USSD  . . . . . . . . . . . . . . . .  8
   6.  Encoding of CoAP for non-IP transports . . . . . . . . . . . .  9
     6.1.  Encoding of CoAP for SMS transport . . . . . . . . . . . .  9
     6.2.  Encoding of CoAP for USSD transport  . . . . . . . . . . . 10
   7.  Message Size Implementation Considerations . . . . . . . . . . 10
   8.  Addressing . . . . . . . . . . . . . . . . . . . . . . . . . . 10
   9.  Options  . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     9.1.  New Options for mixed IP/non-IP operation. . . . . . . . . 11
   10. Protocol Constants . . . . . . . . . . . . . . . . . . . . . . 11
   11. Multicast  . . . . . . . . . . . . . . . . . . . . . . . . . . 11
   12. Proxying Considerations  . . . . . . . . . . . . . . . . . . . 11
   13. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
   14. Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   15. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
   16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     16.1. Normative References . . . . . . . . . . . . . . . . . . . 12
     16.2. Informative References . . . . . . . . . . . . . . . . . . 13
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13









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1.  Introduction

   This specification details the usage of the Constrained Application
   Protocol on the Short Message Service (SMS) or Unstructured
   Supplementary Service Data (USSD) of mobile cellular networks.

1.1.  Motivation

   In some M2M environments, internet connectivity is not supported by
   the constrained end-points, but a cellular network connection is
   supported instead.  Internet connectivity might also be switched off
   for power saving reasons or the cellular coverage does not allow for
   Internet connectivity.  In these situations, SMS and USSD will be
   supported, instead of UDP/IP over GPRS, HSPA or LTE.

   In Open Mobile Alliance (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_ts23_888] for Key Issue on Machine Type
   Communication (MTC) Device Trigger and the proposed solutions in
   Sections 6.2, 6.42, 6.44, 6.48, 6.52, 6.60, and 6.61).  In
   [3gpp_ts23_682] 'Architecture Enhancements to facilitate
   communications with Packet Data Networks and Applications' SMS is at
   the moment the only Trigger Delivery (Trigger Delivery using T4).
   USSD does seem to be in standardisation as a solution for MTC Device
   Trigger.

   M2M protocols using SMS, e.g. for telematics, are using mostly
   various diverse proprietary and closed binary protocols with limited
   publicly available documentation at the moment.

   USSD is a very basic service in mobile networks which uses fewer
   network components to provide a service similar to SMS.  This makes
   USSD very cheap for mobile network operators and chipset manufactures
   as they do not have to provide additional infrastructure.  This is
   why USSD is from a technical point of view supported by all handsets
   and other mobile devices in all networks.

   Where SMS are normally stored in the SMS-C before the actual delivery
   takes place, USSD messages are not stored but delivered immediately.
   If it is impossible to deliver a USSD message within the first
   attempt, delivery fails.  This could be a problem, but could also be
   seen as an advantage as long as delivery problems are covered by
   higher level protocols, such as CoAP.  Without store-and-forward
   mechanisms the delivery is absolutely deterministic.  There is only



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   "success" or "failure" and no "wait a minute".


2.  Terminology

   The terms CoAP Server and CoAP Client are used synonymously to Server
   and Client as specified in the terminology section of
   [I-D.ietf-core-coap].


3.  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].


4.  Scenarios

   Several scenarios are presented first for M2M communications with
   CoAP.  First Mobile-Originating Mobile-Terminating (MO-MT) scenarios
   are presented, where both CoAP endpoints are in devices in a cellular
   network.  Next, Mobile-Terminating (MT) scenarios are detailed, where
   only the CoAP server is in a cellular network.  Finally, Mobile-
   Originating (MO) scenarios where the CoAP client is in the cellular
   network.

4.1.  MO-MT 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            CoAP-REQ
               +------+   (SMS)   +-------+   (SMS)  +------+
               |  A   | --------> | SMS-C | -------> |  B   |
               |(cell)| <-------- |       | <------- |(cell)|
               +------+ CoAP-RES  +-------+ CoAP-RES +------+
                          (SMS)               (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 Response using GPRS transport.
   (depicted in Figure 2).





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

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

   The support for GPRS for the CoAP responses might be useful, so as to
   use SMS only for the request and as a wake-up signal for the device
   hosting the CoAP server.  That device could then initiate a PDP
   context with the cellular network in order to bring up Internet
   connectivity.  After having setup Internet connectivity, further
   message exchange can fully rely on IP.  Network initiated PDP
   contexts could partly obsolete this mechanism.

4.2.  MT Scenarios

   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.  Short Message Peer-to-Peer (SMPP [smpp]), Computer
   Interface to Message Distribution (CIMD [cimd]), Universal Computer
   Protocol/External Machine Interface (UCP/EMI [ucp])) to submit an SMS
   for delivery, which contains the CoAP Request (depicted in Figure 3).

                         CIMD               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).









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

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

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

             HTTP-REQ                 CIMD            CoAP-REQ
   +------+ (CoAP-DATA) +----------+  SMPP   +-----+ (SMS/USSD) +------+
   |      |             | SMS/USSD |  SS7    |SMS-C|            |      |
   |  A   | ----------> | Service  | ------> |  /  | ---------> |  B   |
   | (IP) | <---------- | Provider | <------ | HLR | <--------- |(cell)|
   +------+  HTTP-RES   +----------+         +-----+  CoAP-RES  +------+
            (CoAP-DATA)                              (SMS/USSD)

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

4.3.  MO Scenarios

   A mobile cellular terminal and an IP host communicate by exchanging
   CoAP Request and Response.  The mobile cellular terminal sends a CoAP
   Request in an SMS, which is in turn forwarded by the SMS-C (e.g. with
   Short Message Peer-to-Peer (SMPP [smpp]), Computer Interface to
   Message Distribution (CIMD [cimd]), Universal Computer Protocol/
   External Machine Interface (UCP/EMI [ucp])) as depicted in Figure 6).
   This scenario can be a fall-back for mobile-originating
   communication, when IP connectivity cannot be setup (e.g. due to
   missing coverage).

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

         Figure 6: Cellular and IP Communication (only SMS-based)



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   There are service providers offering SMS and/or USSD delivery and
   notification using an HTTP/REST interface (depicted in Figure 7).

              CoAP-REQ             CIMD                HTTP-REQ
    +------+ (SMS/USSD) +-------+  SMPP  +----------+ (CoAP-DATA) +----+
    |      |            | SMS-C |  SS7   | SMS/USSD |             |    |
    |  A   | ---------> |   /   | -----> | Service  | ----------> | B  |
    |(cell)| <--------- |  HLR  | <----- | Provider | <---------- |(IP)|
    +------+  CoAP-RES  +-------+        +----------+  HTTP-RES   +----+
             (SMS/USSD)                               (CoAP-DATA)

    Figure 7: IP and Cellular Communication (only SMS/USSD-based, using
                       an SMS/USSD service provider)

   If IP connectivity can be setup by the mobile cellular device, the
   complete communication can be handled using UDP/IP by employing
   regular CoAP [I-D.ietf-core-coap] (depicted in Figure 8.

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

           Figure 8: Cellular and IP Communication (GPRS-based)


5.  Message Exchanges

5.1.  Message Exchange for SMS in a Cellular-To-Cellular Mobile-
      Originated and Mobile-Terminated Scenario

   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-- |                        |
             |                       |                        |




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                     Figure 9: 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 [3gpp_ts_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_ts_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.

5.2.  Message Exchange for USSD

   The message exchange for USSD is shown simplified in Figure 10 and
   Figure 11.  The communication between MS, MSC, VLR, HLR, and USSD-GW
   is based on SS7 signalling and the communication between USSD-GW is
   based on IP.  Messages ending with _RPC are Remote Procedure Calls
   (e.g.  REST); messages without _RPC are SS7 signalling.

   Message Sequence Charts with more details can be found in
   [3gpp_ts23_090].

   In Figure 10 the message sequence chart for the USSD transport
   (Mobile Originated) is shown.








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           MS/CoAP CLIENT   MSC/VLR/HLR/USSD-GW         CoAP SERVER
               |                    |                        |
               | ---USSD_REQUEST--> |                        |
               |                    |                        |
               |                    | ---USSD_REQUEST_RPC--> |
               |                    | <--USSD_RESPONSE_RPC-- |
               |                    |                        |
               | <--USSD_RESPONSE-- |                        |
               |                    |                        |

          Figure 10: CoAP Messages over USSD (Mobile Originated)

   In Figure 11 the message sequence chart for the USSD transport
   (Mobile Terminated) is shown.

           MS/CoAP SERVER   MSC/VLR/HLR/USSD-GW         CoAP CLIENT
               |                    |                        |
               |                    | <--USSD_REQUEST_RPC--- |
               |                    |                        |
               | <--USSD_REQUEST--- |                        |
               | ---USSD_RESPONSE-> |                        |
               |                    |                        |
               |                    | ---USSD_RESPONSE_RPC-> |
               |                    |                        |

          Figure 11: CoAP Messages over USSD (Mobile Terminated)


6.  Encoding of CoAP for non-IP transports

6.1.  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.







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6.2.  Encoding of CoAP for USSD transport

   The encoding of USSD data is identical to the encoding of SMS.


7.  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]

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

   There is no possibility to concatenate messages with USSD, thus the
   only option would be CoAP Block is necessary.


8.  Addressing

   For SMS 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.

   For mobile-originated USSD the addressing is done by a so called
   application numbers.


9.  Options

   Uri-Host: The Uri-Host option SHOULD only be sent, in case of
   proxying.  If no proxying is intended the option SHOULD NOT BE set.

   Uri-Port: The Uri-Host option SHOULD only be sent, in case of
   proxying.  If no proxying is intended the option SHOULD NOT BE set.

   End-points receiving CoAP messages over SMS with such options MUST
   behave as specified in [I-D.ietf-core-coap].





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9.1.  New Options for mixed IP/non-IP operation.

   When CoAP should be used in mixed IP and non-IP mode (e.g.  SMS/USSD
   and GPRS as in Figure 2 and Figure 4) the server needs to be informed
   about the client's other address that should be used for the CoAP
   response.  For this reason the new options Reply-To-Uri-Host and
   Reply-To-Uri-Port are proposed.

   OPEN QUESTION: Are CoAP user option numbers applicable here?

   +--------+----------+-------------------+--------+--------+---------+
   | Number |    C/E   |        Name       | Format | Length | Default |
   +--------+----------+-------------------+--------+--------+---------+
   |   TBD  | Critical | Reply-To-Uri-Host | string |  1-270 |  (none) |
   |        |          |                   |        |    B   |         |
   |   TBD  | Critical | Reply-To-Uri-Port |  uint  |  0-2 B |   5683  |
   +--------+----------+-------------------+--------+--------+---------+

                     Table 1: New CoAP Option Numbers


10.  Protocol Constants

   It is RECOMMENDED to configure the RESPONSE_TIMEOUT variable for a
   higher duration than specified in [I-D.ietf-core-coap] for the
   applications described here.  The actual value SHOULD be chosen based
   on experience with SMS, USSD and GPRS.


11.  Multicast

   Multicast MUST NOT be used with the SMS and USSD transports.


12.  Proxying Considerations

   In case of non-IP transport, several use cases might arise for
   proxies:

   o  For a CoAP IP Client and a Mobile Terminated CoAP Server: An HTTP-
      CoAP Proxy at the mobile network / IP network border.

   o  For a Mobile Originated CoAP Client and (CoAP/HTTP) IP Server: A
      CoAP-CoAP or CoAP-HTTP Proxy at the mobile network and IP network
      border or in the server network.

   o  If an LLN is attached to the Mobile: A CoAP-CoAP Proxy into the
      LLN.



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13.  IANA Considerations

   This memo currently includes no request to IANA.  If Reply-To-Uri-
   Host and Reply-To-Uri-Port are deemed useful and decision is taken
   not to have CoAP user options, it might include IANA requests.


14.  Security Considerations

   Security mechanisms defined in [3gpp_ts23_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.


15.  Acknowledgements

   This document is partly 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.

   The authors of this draft would like to thank Bert Greevenbosch,
   Marcus Goetting and Nils Schulte for the discussion.


16.  References

16.1.  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.

   [3gpp_ts23_090]
              ETSI 3GPP, "Technical Specification: Digital cellular
              telecommunications system (Phase 2+); Universal Mobile
              Telecommunications System (UMTS); Unstructured
              Supplementary Service Data (USSD); Stage 2 (3GPP TS 23.090
              version 10.0.0 Release 10)", 2011.



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   [I-D.ietf-core-block]
              Bormann, C. and Z. Shelby, "Blockwise transfers in CoAP",
              draft-ietf-core-block-08 (work in progress),
              February 2012.

   [I-D.ietf-core-coap]
              Frank, B., Bormann, C., Hartke, K., and Z. Shelby,
              "Constrained Application Protocol (CoAP)",
              draft-ietf-core-coap-08 (work in progress), October 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.

16.2.  Informative References

   [3gpp_ts23_682]
              ETSI 3GPP, "Technical Specification Group Services and
              System Aspects; Architecture Enhancements to facilitate
              communications with Packet Data Networks and Applications;
              (Release 11)", 2012.

   [3gpp_ts23_888]
              ETSI 3GPP, "Technical Specification Group Services and
              System Aspects; System Improvements for Machine-Type
              Communications; (3GPP TR 23.888 version 1.6.0, Release
              11)", 2011.

   [3gpp_ts_23_040]
              3GPP, "Technical realization of the Short Message Service
              (SMS)", 3GPP-23.040 a00, Mar 2011.

   [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.









Becker, et al.          Expires September 2, 2012              [Page 13]


Internet-Draft             CoAP SMS/USSD/GPRS                 March 2012


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


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

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


   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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