Internet DRAFT - draft-li-core-coap-over-sms
draft-li-core-coap-over-sms
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.
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This Internet-Draft will expire on April 23, 2012.
Copyright Notice
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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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