This application note describes how to interface the CY7B951 SONET/SDH Serial Transceiver (SST™) with other physical- layer devices. The SST performs clock and data recovery from a SONET/SDH (Synchronous Optical NETwork/Synchronous Digital Hierarchy) 51.84 Mb/s or 155.52 Mb/s interface and can be used in a variety of SONET and ATM applications. The application note will begin with a brief introduction to the SST. Next, interface examples will be given that illustrate how to connect the SST to three different ATM controller devices; the first from PMC-Sierra called the PM5345 SUNI, the second, also from PMC-Sierra, called the S/UNI-LITE, and the third from Integrated Telecom Technologies (IgT) called the WAC-013.