Page "Asynchronous Transfer Mode" Paragraph 11

The design of ATM aimed for a low-jitter network interface.

However, " cells " were introduced into the design to provide short queuing delays while continuing to support datagram traffic.

ATM broke up all packets, data, and voice streams into 48-byte chunks, adding a 5-byte routing header to each one so that they could be reassembled later.

The choice of 48 bytes was political rather than technical.

When the CCITT ( now ITU-T ) was standardizing ATM, parties from the United States wanted a 64-byte payload because this was felt to be a good compromise in larger payloads optimized for data transmission and shorter payloads optimized for real-time applications like voice ; parties from Europe wanted 32-byte payloads because the small size ( and therefore short transmission times ) simplify voice applications with respect to echo cancellation.

Most of the European parties eventually came around to the arguments made by the Americans, but France and a few others held out for a shorter cell length.

With 32 bytes, France would have been able to implement an ATM-based voice network with calls from one end of France to the other requiring no echo cancellation.

48 bytes ( plus 5 header bytes