CoRE K. Li
Internet-Draft Huawei Technologies
Intended status: Standards Track X. Sun
Expires: July 30, 2013 China Telecom
January 26, 2013
CoAP Payload-Length Option Extension
draft-li-core-coap-payload-length-option-01
Abstract
This document defines an extension to the Constrained Application
Protocol (CoAP) to add one new option: Payload-Length, which is used
to indicate the length of the payload of the message.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Justification . . . . . . . . . . . . . . . . . . . . . . . 3
1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
1.4. Requirements Language . . . . . . . . . . . . . . . . . . . 3
2. Option Definition . . . . . . . . . . . . . . . . . . . . . . . 4
3. Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5
7. Normative References . . . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6
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1. Introduction
This specification adds one new option to the Constrained Application
Protocol (CoAP): Payload-Length.
1.1. Motivation
If a CoAP message is transported through UDP, the message length can
be obtained from the UDP header. But not all transport mechanisms
provide an unambiguous length of the CoAP message. For example, in
industry field, there are some data tranport protocols, like RS232,
RS422, RS485, which don't provide message length indication. For
these cases, an indication of the payload length of the message is
needed in CoAP message level.
TBD: how about CAN bus protocol, USB 2.0?
With this option, it will be easier for the receiver to extract the
payload part from the whole message.
Another benefit to have this option is to check the integrity of the
message length.
1.2. Justification
To indicate the payload length, another alternative is to use
encoding method as specified in section 3.2 of [I-D.ietf-core-coap],
but it is better to use an Option for this.
Reason is that, payload length is an optional feature, and in most of
the cases, it is not necessary to be indicated. If we use encoding
method, every implementation needs to support this encoding for the
payload, not only for the options. If we use an Option for this, it
is optional, and it can be optionally implemented where necessary.
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