CoAP Implementation Guidance
draft-ietf-lwig-coap-06
LWIG Working Group M. Kovatsch
Internet-Draft ETH Zurich
Intended status: Informational O. Bergmann
Expires: January 3, 2019 C. Bormann, Ed.
Universitaet Bremen TZI
July 02, 2018
CoAP Implementation Guidance
draft-ietf-lwig-coap-06
Abstract
The Constrained Application Protocol (CoAP) is designed for resource-
constrained nodes and networks such as sensor nodes in a low-power
lossy network (LLN). Yet to implement this Internet protocol on
Class 1 devices (as per RFC 7228, ~ 10 KiB of RAM and ~ 100 KiB of
ROM) also lightweight implementation techniques are necessary. This
document provides lessons learned from implementing CoAP for tiny,
battery-operated networked embedded systems. In particular, it
provides guidance on correct implementation of the CoAP specification
RFC 7252, memory optimizations, and customized protocol parameters.
Status of This Memo
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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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Kovatsch, et al. Expires January 3, 2019 [Page 1]
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Protocol Implementation . . . . . . . . . . . . . . . . . . . 4
2.1. Client/Server Model . . . . . . . . . . . . . . . . . . . 4
2.2. Message Processing . . . . . . . . . . . . . . . . . . . 5
2.2.1. On-the-fly Processing . . . . . . . . . . . . . . . . 5
2.2.2. Internal Data Structure . . . . . . . . . . . . . . . 6
2.3. Message ID Usage . . . . . . . . . . . . . . . . . . . . 7
2.3.1. Duplicate Rejection . . . . . . . . . . . . . . . . . 7
2.3.2. MID Namespaces . . . . . . . . . . . . . . . . . . . 8
2.3.3. Relaxation on the Server . . . . . . . . . . . . . . 8
2.3.4. Relaxation on the Client . . . . . . . . . . . . . . 9
2.4. Token Usage . . . . . . . . . . . . . . . . . . . . . . . 10
2.4.1. Tokens for Observe . . . . . . . . . . . . . . . . . 11
2.4.2. Tokens for Blockwise Transfers . . . . . . . . . . . 12
2.5. Transmission States . . . . . . . . . . . . . . . . . . . 12
2.5.1. Request/Response Layer . . . . . . . . . . . . . . . 12
2.5.2. Message Layer . . . . . . . . . . . . . . . . . . . . 13
2.6. Out-of-band Information . . . . . . . . . . . . . . . . . 14
2.7. Programming Model . . . . . . . . . . . . . . . . . . . . 15
2.7.1. Client . . . . . . . . . . . . . . . . . . . . . . . 16
2.7.2. Server . . . . . . . . . . . . . . . . . . . . . . . 16
3. Optimizations . . . . . . . . . . . . . . . . . . . . . . . . 17
3.1. Message Buffers . . . . . . . . . . . . . . . . . . . . . 17
3.2. Retransmissions . . . . . . . . . . . . . . . . . . . . . 18
3.3. Observable Resources . . . . . . . . . . . . . . . . . . 18
3.4. Blockwise Transfers . . . . . . . . . . . . . . . . . . . 19
3.4.1. Generic Proxying of Block Messages . . . . . . . . . 19
3.4.2. Atomic Blockwise Operations . . . . . . . . . . . . . 20
3.5. Deduplication with Sequential MIDs . . . . . . . . . . . 20
4. Alternative Configurations . . . . . . . . . . . . . . . . . 23
4.1. Transmission Parameters . . . . . . . . . . . . . . . . . 23
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