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).


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