SONET, used in North America, and SDH, used in Europe, are almost identical standards for the transport of data over optical media between two fixed points. They use 810-byte frames as a container for the transport of data at speeds of up to 9.6 Gbps. .
SONET/SDH is used as the bearer layer for higher-layer protocols such as ATM or IP/PPP, employed on devices that switch or route traffic to a particular end point. The functions of SONET/SDH in the broadband arena are roughly analogous to those of T1/E1 in the narrowband world. The SONET/SDH standards define the packaging of data within SONET/SDH frames, the encoding of signals on a fiber-optic cable, and the management of the SONET/SDH link. .
The advantages of SONET/SDH include the following: .
• rapid point-to-point transport of data with little overhead.
• standards-based multiplexing of SONET/SDH datastreams .
• transport independent from the services and applications that it supports .
• self-healing ring structure to reroute traffic around faults within a particular link .
• widely deployed transmission infrastructure within carrier networks .
• TDM grooming and aggregation from the DS0 level.
Figure 1: A SONET/SDH Pipe Carrying ATM .
.
Transporting IP over SONET/SDH:.
The terms IP over SONET/SDH or packet over SONET/SDH as they are used in the industry today, refer essentially to the addition of SONET/SDH interfaces to a router that terminates the PPP. Faster routing represents a natural migration for original network-routing equipment, and, with the widespread adoption of PPP as a framing protocol for IP traffic, it made sense to combine the two standards to create devices for the rapid transport of IP traffic from point to point. .
IP traffic on a SONET/SDH router is treated as a serial datastream that travels hop by hop through the network using PPP for its framing and encapsulation functions.
