Page 116 - Optical Switching And Networking Handbook

05_200023_CH04/Batesx 1/17/01 8:18 AM Page 101

Synchronous Digital Hierarchy 101

easier to extract and insert low-bit-rate services into or from the
higher-speed services.

High reliability means high availability. With the SDH networks,
providers can meet the demands of their customers faster, better,
and cheaper. The providers now can use a standard set of
equipment to meet the need, eliminating the need for multiple
spares and different operations systems. Moreover, with the
automatic protection switching (APS) services of the SDH, the
network can heal itself when a component fails. This means that
the customer never realizes that a network error or failure has
occurred.
Future networking equipment will be based on multiples of
the SDH and SONET equipment. The perfect platform for the
carriers is one that satisfies the demand without changes en
masse. SDH can satisfy the basic telephony needs, low- and
high-speed data communications demands, and the newer
demands of the Internet, specifically for streaming audio and
video capabilities. This also meets the need for video or
multimedia on-demand services, only recently becoming more
popular.
Three words are crucial to network operators and end users alike:
bandwidth, bandwidth, bandwidth. The need for bandwidth cannot
be overstated in the network today. There is never too much, only
enough to satisfy the current need. As we see use of the networks
increasing, the carriers and manufacturers are continually develop-
ing new SDH speeds and multiplexing rates to meet that demand.
Recently, OC-768 in SONET and SDH-256 were developed to support
up to 40 Gbps on a multiplexed circuit. Add to this the ability to per-
form multiple wavelength multiplexing on a single piece of fiber, and
we have the potential for terabits per second. That will hold us for a
short term; however, telecommunications services are like water, and
water seeks its own level. Thus telecommunications services will
increase when we have more bandwidth until we consume it all.Then
it is back to the drawing board to develop a new technique to increase
the capacities again. This is a vicious circle, but one that is also
extremely exciting as the thresholds are pushed to new levels and
limits.