Page 150 - Optical Switching And Networking Handbook

07_200023_CH06/Batesx 1/17/01 10:05 AM Page 135

Optical Switching Systems and Technologies 135

In ring interconnection, optical switching systems operate
as SONET switches, providing integrated management of optical
circuits spanning multiple rings. These switches will support the
following:

Automated provisioning of OC-n circuits in the metropolitan area
Varying levels of restoration on SONET rings
Diversely routed 1 1 protection
Mesh-based protection using Datacomm routing protocols

Bottlenecks at the Switch

One potential technology bottleneck is that of telecom switches, the
essential network elements that enable traffic to be routed from a
source to a destination. An optical cross-connect switch may be
thought of as a black box with multiple input and output fibers car-
rying network traffic.The basic function of the switch is to enable the
signal on any one of the input fibers to be redirected to any one of the
output fibers in the manner configured by the users.
The optical cross-connect switches used in today’s networks rely
on electronic cores. An optical signal arriving at a switch input port
is converted to an electronic signal by a high-speed photo detector
(receiver). Electronic circuits in the switch core then direct the signal
to the desired output port. A final electrical-to-optical conversion is
performed by a laser diode, transforming the signal back into light
for onward transmission on the fiber network.
The fundamental problem with these electronic cores is that they
do not scale well to large port counts (numbers of input and output
channels) and are costly to replace for network upgrades to the
higher data rates needed for the growing demand for bandwidth.
Many workers in the industry now believe that electronic-core cross-
connect switches cannot efficiently meet the needs of tomorrow’s
communication networks, so a major challenge is to develop new, all-
optical switching technologies that can fill this gap. To gain accep-
tance, these new technologies must be able to demonstrate
low-optical-loss switching with extremely high reliability.