Page 276 - Optical Switching And Networking Handbook

11_200023_CH10/Bates 1/17/01 9:06 AM Page 261

The Future of Optical Networking (Where Is It All Heading?) 261

a customer’s window. The optical transceiver consists of both a laser
transmitter and a detector to provide full duplex capability.
Free-space optics enables fast delivery of high-speed access to
buildings. The time and expense of digging up city roads is elimi-
nated. The traditional approach is, however, problematic in that
atmospheric conditions have an impact on the link performance.
Availability is generally determined by the length of the link and fog
conditions. Fog becomes a natural enemy of free space optics. If the
light cannot pass through the air because of the fog, then the system
does not perform.
A couple of companies are now building their networks on the
West Coast to satisfy fast delivery in the local loop. AirFiber uses a
mesh of short, redundant links between their optical transceivers.
The mesh network functionality is provided by compact nodes
mounted on the rooftops of various buildings and connected by line
of sight. The short links yield high over-the-air availability, even in
dense fog. The distances are extremely limited to start. However,
redundant 622-Mbps links between optical transceivers provide
much bandwidth. A representation of this is shown in Figure 10-21.
The optical nodes are positioned on top of buildings.
The AirFiber network is installed on rooftops and aimed at
building-to-building communications as well as in-the-window
communications, as shown in Figure 10-22. Here the systems are
shown in a community of interest to satisfy the short-haul commu-
nications in the city.
The final look at the AirFiber network is shown in Figure 10-23
where the components are separated from the backbone, the access,
and the end-user premises network.
The second company to be aggressively involved is Terabeam.
Their Fiberless Optical(tm) technology closes the last mile gap by
linking customers to inter-city destinations and to WAN and Inter-
net gateways via optical streams that travel through the air. Because
they deliver bandwidth without laying fiber under streets, the opti-
cal bandwidth can be delivered quickly and cost-efficiently. This