sonet

SONET, or Synchronous Optical Networking, is a standardized framework for transmitting multiple digital bit streams over optical fiber using synchronous timing. Developed in the United States for high-bandwidth, reliable telecom transport, it provides a common method for carrying voice, data, and video over long distances. In practice, SONET uses line rates expressed as STS-n frames, with higher-rate signals formed by multiplexing these base frames. The base rate STS-1 is 51.84 Mbit/s, and common higher rates include OC-3 (155.52 Mbit/s), OC-12 (622.08 Mbit/s), OC-48 (2.488 Gbit/s), and OC-192 (9.953 Gbit/s).

The SONET frame contains overhead and payload sections. The overhead carries timing, signaling, and management information, while the payload carries user data. The framing is synchronous, and pointers locate the payload within frames, allowing flexible insertion and extraction of tributary signals. Multiplexing aggregates many lower-rate channels into higher-bandwidth streams, enabling scalable transport.

Topologies supported by SONET include point-to-point and rings. Ring structures often incorporate protection mechanisms (such as one-plus-one or one-for-one) to maintain service in the event of a fiber cut or equipment failure, contributing to network reliability.

Standards and interoperability have shaped the landscape. SONET was standardized in the United States (e.g., ANSI T1.105). Internationally, the Synchronous Digital Hierarchy (SDH) framework developed by ITU-T provides a closely related, interoperable approach. In modern networks, SONET/SDH forms the backbone of optical transport, though newer architectures and technologies have broadened the ecosystem.