Data Communication and Networking – SONET ISDH Study Notes

• Synchronous Optical Network (SONET) is a standard developed by ANSI for fiber-optic networks: Synchronous Digital Hierarchy (SDH) is a similar standard developed by ITU-T.
• SONET has defined a hierarchy of signals called synchronous transport signals (STSs). SDH has defined a similar hierarchy of signals called synchronous transfer modules (STMs).
• An OC-n signal is the optical modulation of an STS-n (or STM-n) signal.
• SONET defines four layers: path, line, section, and photonic.
• SONET is a synchronous TDM system in which all clocks are locked to a master clock.
• A SONET system can use the following equipment: 1. STS multiplexers 2. STS demultiplexers 3. Regenerators 4. Add/drop multiplexers 5. Terminals
• SONET sends 8000 frames per second; each frame lasts 125 IlS.
• An STS-I frame is made of 9 rows and 90 columns; an STS-n frame is made of 9 rows and n x 90 columns.
• STSs can be multiplexed to get a new STS with a higher data rate.
• SONET network topologies can be linear, ring, or mesh.
• A linear SONET network can be either point-to-point or multipoint.
• A ring SONET network can be unidirectional or bidirectional.
• To make SONET backward-compatible with the current hierarchy, its frame design includes a system of virtual tributaries (VTs).