Sunday, August 15, 2010
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SONET and SDH were formerly designed to transport circuit mode communications (e.g., T1, T3) from a mixture of different sources. The primary difficulty in doing this prior to SONET/SDH was that the synchronization sources of these different circuits were different. This intended each circuit was actually operating at a slightly different rate and with different phase. SONET/SDH allowed for the simultaneous transport of many different circuits of differing origin within one single framing protocol. In a sense, then, SONET/SDH is not itself a communications protocol per se, but a transport protocol.
Due to SONET/SDH's vital protocol impartiality and transport-oriented features, SONET/SDH was the obvious choice for transporting Asynchronous Transfer Mode (ATM) frames. It rapidly evolved mapping structures and concatenated payload containers to transport ATM connections. In other words, for ATM (and eventually other protocols such as TCP/IP and Ethernet), the internal complex structure previously used to transport circuit-oriented connections is removed and replaced with a large and concatenated frame (such as STS-3c) into which ATM frames, IP packets, or Ethernet are placed.
A rack of Alcatel STM-16 SDH add-drop multiplexers
Both SDH and SONET are widely used today. SONET in the U.S. and Canada and SDH in the rest of the world. Although the SONET standards were developed before SDH, their relative penetrations in the worldwide market dictate that SONET is considered the variation.
The two protocols are standardized according to the following:
• Synchronous Digital Hierarchy (SDH) standard was originally defined by the ETSI or European Telecommunications Standards Institute
• Synchronous Optical Networking (SONET) standard as defined by GR-253-CORE from Telcordia and T1.105 from American National Standards Institute
Synchronous Optical Networking
SONET and SDH were formerly designed to transport circuit mode communications (e.g., T1, T3) from a mixture of different sources. The primary difficulty in doing this prior to SONET/SDH was that the synchronization sources of these different circuits were different. This intended each circuit was actually operating at a slightly different rate and with different phase. SONET/SDH allowed for the simultaneous transport of many different circuits of differing origin within one single framing protocol. In a sense, then, SONET/SDH is not itself a communications protocol per se, but a transport protocol.
Due to SONET/SDH's vital protocol impartiality and transport-oriented features, SONET/SDH was the obvious choice for transporting Asynchronous Transfer Mode (ATM) frames. It rapidly evolved mapping structures and concatenated payload containers to transport ATM connections. In other words, for ATM (and eventually other protocols such as TCP/IP and Ethernet), the internal complex structure previously used to transport circuit-oriented connections is removed and replaced with a large and concatenated frame (such as STS-3c) into which ATM frames, IP packets, or Ethernet are placed.
A rack of Alcatel STM-16 SDH add-drop multiplexers
Both SDH and SONET are widely used today. SONET in the U.S. and Canada and SDH in the rest of the world. Although the SONET standards were developed before SDH, their relative penetrations in the worldwide market dictate that SONET is considered the variation.
The two protocols are standardized according to the following:
• Synchronous Digital Hierarchy (SDH) standard was originally defined by the ETSI or European Telecommunications Standards Institute
• Synchronous Optical Networking (SONET) standard as defined by GR-253-CORE from Telcordia and T1.105 from American National Standards Institute
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