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 Becker, et al. Expires April 26, 2012 [Page 1] Internet-Draft CoAP SMS/GPRS October 2011 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 Becker, et al. Expires April 26, 2012 [Page 2] Internet-Draft CoAP SMS/GPRS October 2011 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). Becker, et al. Expires April 26, 2012 [Page 3] Internet-Draft CoAP SMS/GPRS October 2011 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. Becker, et al. Expires April 26, 2012 [Page 4] Internet-Draft CoAP SMS/GPRS October 2011 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. Becker, et al. Expires April 26, 2012 [Page 5] Internet-Draft CoAP SMS/GPRS October 2011 +--------+----------+-------------------+--------+--------+---------+ | 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 Becker, et al. Expires April 26, 2012 [Page 6] Internet-Draft CoAP SMS/GPRS October 2011 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. Becker, et al. Expires April 26, 2012 [Page 7] Internet-Draft CoAP SMS/GPRS October 2011 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 Becker, et al. Expires April 26, 2012 [Page 8]