Stateful Observation in CoAP

Document Type Expired Internet-Draft (individual)
Last updated 2013-12-26 (latest revision 2013-06-24)
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The Observe Option allows a CoAP client to observe changes in the state of resources and obtain a current representation of the last resource state. To be an observer of an origin server's resources, the client is required to register its interest with the server. A successful registration will make the client added into the server's observation list, while a failed one MAY drive the client to re- register. However, repeated and frequent re-registrations cannot guarantee the client to eventually become an observer of the target server. In the case that the server is unable or unwilling to accept an observer, the time-intensive re-registrations will just bring redundant messages in the constrained network and considerable energy consumption on both the client and the server. This memo defines a new CoAP option, State, for providing stateful observation on the resources of CoAP servers. By observing the state of the server in terms of the Observe Option, a client can explicitly learn when the server will not actively reject an observation registration, and then can wisely performs the re-registration. This avoids the potential registration flooding that causes considerable network overhead and energy consumption on the constrained nodes.


Changsha Ma (
Peilin Hong (
Kaiping Xue (

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