Final answer:
The payload of an ATM cell is 48 bytes. Including the 5-byte header, the total size of an ATM cell is 53 bytes.
Step-by-step explanation:
The size of the payload part of an Asynchronous Transfer Mode (ATM) cell is 48 bytes. An ATM cell is made up of a 5-byte header and a 48-byte payload, totaling 53 bytes. The header contains information such as the virtual path identifier and virtual channel identifier, which are used for routing the cell through an ATM network. The payload carries the actual user data. This standardized structure allows for the efficient, fixed-size cell relay and is particularly well-suited for network traffic that requires predictable service, like voice and video transmissions.