Message Format of CoAP

CoAP messages are encoded in binary-format or 0/1 format. Like other message formats, CoAP message has a header and a payload section along with an optional section.

The size of CoAP header is 4 bytes or 32 bits. This size is fixed for every CoAP message. Whereas the other part of message is the optional part which includes payload and tokens of variable size ranging from 0-8 bytes.

The message format of CoAP contains the following fields:

  • Version – The size of version field is 2 bits. It represents the version of the CoAP protocol.
  • Type Code – The size of type field is 2 bits. There are four types of messages namely confirmable, non-confirmable, acknowledgement and reset represented by the bit patterns 00, 01, 10, 11 respectively.
  • Option Count – The size of option count field is 4 bits. These 4 bits, means there could be a total of 16 possible options in header.
  • Code – The size of code field is 8 bits. This indicates whether message is empty, request message or response message.
  • Message ID – The size of message ID field is 16 bits. It is used to detect the message duplication and types of messages.
  • Tokens [Optional] – The size of tokens field is variable which ranges from 0-8 bytes. It’s used to match a response with request.
  • Options [Optional] – The options field in CoAP message has a variable size. It defines the type of payload message.
  • Payload [Optional] – Similar to options field, the payload field has a variable size. The payload of requests or of responses is typically a representation of the requested resource or the result of the requested action.

CoAP Message Format

Constrained Application Protocol (CoAP)

There are several protocols in the application layer of the Internet protocol suite. One such useful protocol is the CoAP or Constrained Application Protocol. This protocol has a wide range of advantages and applications in the field of the Internet of Things (IoT) and cloud computing. CoAP also has a powerful contribution in providing versatile solutions to IoT applications.
This article delves into a set of key topics and fundamental concepts in CoAP protocol along with its applications in the real world.

Similar Reads

What is CoAP?

CoAP or Constrained Application Protocol, as the name suggests, is an application layer protocol that was introduced by the Internet Engineering Task Force in the year 2014. CoAP is basically designed for the constrained environment....

Methods in CoAP

CoAP is a web-based protocol. This means CoAP resembles the HTTP protocol and is capable to utilize the HTTP methods.These methods are-...

Message Format of CoAP

CoAP messages are encoded in binary-format or 0/1 format. Like other message formats, CoAP message has a header and a payload section along with an optional section....

Applications of CoAP

Real Time Monitoring in Grid – Smart cities can monitor the distribution and generation of power remotely. The CoAP sensors could be embedded inside the transformers and the data could be transferred over GPRS or 6LowPAN. Defense utilities – The armory and tanks are now-a-days fitted with sensors so that information could be communicated remotely without any interference. The CoAP sensors could detect any intrusion. This makes them capable to transfer more data even under low bandwidth network. Aircraft utilities – The Aircraft sensors and actuators could be connected with other sensors and communication can take place using smart CoAP based sensors and actuators....

Conclusion

A lot of modern world tasks could be eased out with the help of CoAP protocols. Due to less overhead and capability to transfer data effectively even under low bandwidth, CoAP has became a primarily choice for IoT and cloud computing system architecture. CoAP messages have a fixed size header which is of 4 bytes. Alongside this, CoAP message format have some optional fields which includes fields like token, options, and payload. This message format of CoAP is binary encoded in 0/1 format. CoAP works on request response model which majorly resembles HTTP methods like GET, POST, PUT, and DELETE along with its own unique method Observe...

Frequently Asked Questions on CoAP – FAQs

What is CoAP?...