Editing Measuring network throughput (section)

====ATM====

[[Asynchronous Transfer Mode]] (ATM) uses a radically different method of carrying data. Rather than using variable length frames or packets, data is carried in fixed size cells. Each cell is 53 bytes long, with the first 5 bytes defined as the header, and the following 48 bytes as payload. [[Computer networking|Data networking]] commonly requires packets of data that are larger than 48 bytes, so there is a defined adaptation process that specifies how larger packets of data should be divided up in a standard manner to be carried by the smaller cells. This process varies according to the data carried, so in ATM nomenclature, there are different [[ATM Adaptation Layers]]. The process defined for most data is named ATM Adaptation Layer No. 5 or [[AAL5]].

Understanding throughput on ATM links requires a knowledge of which ATM adaptation layer has been used for the data being carried.<ref>Comer, D. E. (2008). Computer Networks and Internets 5th Edition</ref>