In CoAP Message Format, Token length isa.4 byteb.4 bitc.2 bitd.2 byteCLEAR MY CHOICE

Breakdown of the Problem

We need to determine the correct length of the Token in the CoAP (Constrained Application Protocol) message format. The options provided are related to the size of the Token in bytes and bits.

Relevant Concepts

In the CoAP message format, the Token is used for matching response messages with requests. The length of the Token can vary but is limited according to the CoAP specifications.

Analysis and Detail

1. Understanding Token Length: The CoAP Token can range from 0 to 8 bytes in length, depending on how the application designates it. Thus, we need to analyze the available answer options.

2. Evaluate Answer Options:

   • a. 4 byte: This would mean the Token is 32 bits long (since $1 \text{ byte} = 8 \text{ bits}$).
   • b. 4 bit: This indicates a very small token length of 1/2 of a byte.
   • c. 2 bit: This is even smaller, representing only a fraction of a byte.
   • d. 2 byte: This implies the Token is 16 bits long.

Verify and Summarize

The typical length of the Token is generally more than just a few bits; hence options b, c, and d are unlikely to be correct. The best choice, although the actual token length can vary up to 8 bytes, is option a, which provides a reasonable maximum length.

Final Answer

The correct answer is: a. 4 byte.