This document is a broad outline of what Synchronous Optical NETwork (SONET) technology is, and how it works.
SONET defines optical signals and a synchronous frame structure for multiplexed digital traffic. It is a set of standards that define the rates and formats for optical networks specified in ANSI T1.105, ANSI T1.106, and ANSI T1.117.
A similar standard, Synchronous Digital Hierarchy (SDH), is used in Europe by the International Telecommunication Union Telecommunication Standardization Sector (ITU−T). SONET equipment is generally used in North America, and SDH equipment is generally accepted everywhere else in the world.
Both SONET and SDH are based on a structure that has a basic frame format and speed. The frame format used by SONET is the Synchronous Transport Signal (STS), with STS−1 as the base−level signal at 51.84 Mbps. An STS−1 frame can be carried in an OC−1 signal. The frame format used by SDH is the Synchronous Transport Module (STM), with STM−1 as the base−level signal at 155.52Mbps. An STM−1 frame can be carried in an OC−3 signal.