Page "Asynchronous Transfer Mode" Paragraph 5

At the time of the design of ATM, 155 Mbit / s Synchronous Digital Hierarchy ( SDH ) with 135 Mbit / s payload was considered a fast optical network link, and many Plesiochronous Digital Hierarchy ( PDH ) links in the digital network were considerably slower, ranging from 1. 544 to 45 Mbit / s in the USA, and 2 to 34 Mbit / s in Europe.