How can you ensure low latency with CoAP protocol in IoT?

1 Use confirmable messages

CoAP supports two types of messages: confirmable and non-confirmable. Confirmable messages require an acknowledgement from the receiver, while non-confirmable messages do not. Confirmable messages are more reliable, but also introduce more overhead and delay. Non-confirmable messages are faster, but also more prone to loss and duplication. To ensure low latency with CoAP protocol in IoT, you should use confirmable messages for critical or sensitive data, such as commands, configuration, or updates, and non-confirmable messages for periodic or redundant data, such as sensor readings, status, or notifications.

2 Adjust retransmission parameters

CoAP uses a simple exponential backoff algorithm to retransmit confirmable messages that do not receive an acknowledgement within a certain time interval. The default values for the initial timeout and the maximum number of retransmissions are 2 seconds and 4, respectively. However, these values may not be optimal for your IoT scenario, depending on the network conditions, the device capabilities, and the application requirements. To ensure low latency with CoAP protocol in IoT, you should adjust the retransmission parameters according to your specific needs and constraints. For example, you can reduce the initial timeout or the number of retransmissions to minimize the waiting time, or increase them to improve the reliability.

3 Use observe option

CoAP supports an observe option that allows a client to subscribe to a resource on a server and receive notifications whenever the resource changes. This is useful for applications that need to monitor the state of a device or a sensor, without polling it frequently. The observe option reduces the network traffic and the power consumption, as well as the latency, since the client does not need to send a request every time it wants to get an update. To ensure low latency with CoAP protocol in IoT, you should use the observe option for resources that change frequently or unpredictably, and that are relevant for your application logic.

4 Use blockwise transfer

CoAP supports a blockwise transfer option that allows a client or a server to split a large message into smaller blocks and send them separately. This is useful for applications that need to transfer large amounts of data, such as firmware updates, images, or videos, over a constrained network. The blockwise transfer option reduces the packet loss and the retransmission overhead, as well as the latency, since the sender does not need to wait for the whole message to be delivered before sending the next one. To ensure low latency with CoAP protocol in IoT, you should use the blockwise transfer option for messages that exceed the network's maximum transmission unit (MTU), or that are likely to encounter fragmentation or congestion.

5 Use compression

CoAP supports a compression option that allows a client or a server to reduce the size of the message headers and the payload, using a predefined or a negotiated compression scheme. This is useful for applications that need to save bandwidth, power, or memory, over a constrained network. The compression option reduces the network load and the transmission time, as well as the latency, since the sender and the receiver can exchange less data. To ensure low latency with CoAP protocol in IoT, you should use the compression option for messages that contain redundant or verbose information, or that can be encoded more efficiently.