Synchronous Optical Networking
SAN Recovery - Synchronous Optical Networking
Synchronous optical networking (SONET) is a type of multiplexing protocol used in transferring digital data using lasers or light-emitting diodes (LEDs) over the same fiber. The synchronous method enables large number of data traffic over the same fiber wire without creating synchronization problems. Synchronous Digital Hierarchy (SDH) is a multiplexing protocol similar to SONET.
SONET is the standard defined by the ANSI T1 for synchronous operation used in North America.
SONET was originally designed to enable simultaneous transport of many different circuits of different origin within one single framing protocol. Because of this, SONET is considered more as a communication protocol than as a transport protocol.
SONET was widely used in Asynchronous Transfer Mode (ATM) applications – thanks to their protocol neutrality and transport-oriented features. Later SONET evolved mapping structures and concatenated payload containers to transport ATM connections. The result was a large and concatenated frame into which ATM frames, IP packets, or Ethernet is placed.
SONET features a multiplexed structure, with a header interleaved between the data in a complex manner. This structure allows encapsulated data to have its own frame rate. It also permits a very low latency for this data. In SONET, the data passing through the equipment is delayed at most by 32 microseconds, compared to the typical frame rate of 125 microseconds.
SONET is evolving to offer more flexible concatenation solutions. Traditional concatenated containers had fixed sizes, so they used to leave a large amount of unused bandwidth during voice and data transmission. Virtual concatenation (VCAT) and Link Capacity Adjustment Scheme (LCAS) are two solutions that address this issue.
