Transport of CoAP over SMS and GPRS
draft-becker-core-coap-sms-gprs-00
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| Document | Type |
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|---|---|---|---|
| Authors | Koojana Kuladinithi , Markus Becker , Thomas Poetsch | ||
| Last updated | 2011-10-24 | ||
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draft-becker-core-coap-sms-gprs-00
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
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and may be updated, replaced, or obsoleted by other documents at any
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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
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publication of this document. Please review these documents
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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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