Abstract
As a lot of sensors are connected to the Internet, many works have been made to support group communication for constrained application protocol. The existing multicast-based group communication may be efficient, but not reliable in wireless sensor networks. The existing unicast-based group communication is reliable, but it tends to give low performance. Recently, an observe-based group communication scheme was proposed, which uses the constrained application protocol–observe option. This is very effective, but tends to generate too many notification messages in the network. In this article, we thus propose an enhanced scheme of the observe-based group communication. In the proposed scheme, a broker is employed to monitor the status information of resources for a group of sensors. Each sensor will update its resource status to the broker using the constrained application protocol–observe option, and the broker sends the aggregate updated information to the constrained application protocol client, as done in the existing observe-based scheme. To reduce the number of notifications between the broker and the client, in the proposed scheme, the broker sends an aggregated notification to the client only when the client requests the information on resource status. In addition, the proposed scheme uses a hash function and the max-age timer of constrained application protocol in order to reduce unnecessary notification messages from the sensors to the broker. For performance analysis, we compare the existing and proposed schemes in terms of total delay and the amount of generated packets. From the results, we can see that the existing and proposed observe-based schemes improve total delay by almost 60%–80%, compared to the existing multicast-based and unicast-based schemes. In terms of the number of generated packets, the proposed scheme improves the existing observed-based scheme by almost 30%. We also performed the testbed experimentation of the proposed scheme for validation in the real-world network.
Highlights
With the popularity of Internet-of-things (IoT) services, the constrained application protocol (CoAP) was developed to support the IoT sensor devices.[1,2,3,4,5,6] The basic communication model for CoAP is based on the client–server model in which a client exchanges messages with a server
The multicast-based group communication may not be reliable in wireless sensor networks, such as low-power and lossy networks (LLNs)
The existing observebased scheme tends to generate a lot of unnecessary notifications even when the sensor value has not been changed
Summary
With the popularity of Internet-of-things (IoT) services, the constrained application protocol (CoAP) was developed to support the IoT sensor devices.[1,2,3,4,5,6] The basic communication model for CoAP is based on the client–server model in which a client exchanges messages with a server. In the usage phase, when the client initially requests a group of resource, the broker will request the resource information to each sensor by sending a GET message with the CoAP observe option. In the existing observe-based group communication, the notifications are periodically generated if the sensor value has not been changed and the max-age timer expires.
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