ü SONET is the TDM optical network standard for North America
ü SONET is called Synchronous Digital Hierarchy (SDH) in the rest of the world
ü SONET is the basic phycal layer standard
ü Other data types such as ATM and IP can be transmitted over SONET
ü OC-1 consists of 810 bytes over 125 us; OC-n consists of 810n bytes over 125 us
ü Linear multiplexing and de-multiplexing is possible with Add-Drop-Multiplexers
ü The SONET/SDH standards enable the interconnection of fiber optic transmission equipment from various vendors through multiple-owner trunk networks.
ü The basic transmission bit rate of the basic SONET signal is
ü In SDH the basic rate is 155.52 Mb/s.
ü OC stands for optical carrier. It has become common to refer to SONET links as OC-N links.
ü The basic SDH rate is 155.52 Mb/s and is called the synchronous transport module—level 1 (STM 1).
SONET ADM is a fully synchronous, byte oriented device, that can be used add/drop OC sub-channels within an OC-N signal
Ex: OC-3 and OC-12 signals can be individually added/dropped from an OC-48 carrier
ü SONET and SDH can be configured as either a ring or mesh architecture
ü SONET/SDH rings are self-healing rings because the traffic flowing along a certain path can be switched automatically to an alternate or standby path following failure or degradation of the link segment
ü Two popular SONET and SDH networks:
– 2-fiber, unidirectional, path-switched ring (2-fiber UPSR)
– 2-fiber or 4-fiber, bidirectional, line-switched ring (2-fiber or 4-fiber BLSR)
Ex: Total capacity OC-12 may be divided to four OC-3 streams, the OC-3 is called a path here
ü Rx compares the signals received via the primary and protection paths and picks the best one
ü Constant protection and automatic switching
ü If a primary-ring device fails in either node 3 or 4, the affected nodes detect a loss-of-signal condition and switch both primary fibers connecting these nodes to the secondary protection pair
ü If an entire node fails or both the primary and protection fibers in a given span are severed, the adjacent nodes switch the primary-path connections to the protection fibers, in order to loop traffic back to the previous node.
In case of failure, the secondary fibers between only the affected nodes (3 & 4) are used, the other links remain unaffected
If both primary and secondary are cut, still the connection is not lost, but both the primary and secondary fibers of the entire ring is occupied
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