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11_200023_CH10/Bates 1/17/01 9:06 AM Page 258

258 Chapter 10

Satisfying the Last Mile

National and international networks send data from city to city over
thousands of miles of fiber at the speed of light. At the urban termi-
nation point of these long-haul networks, the data must traverse the
last mile to reach each customer site. The infrastructure that deliv-
ers data over this last mile is usually unshielded twisted pairs of cop-
per and offers

Low bandwidth
Long lead times to provision

Noisy channels
Error-prone conditions
This does not sound like the goal of high-speed communicators.
Efforts to solve the access problem by extending the fiber cables to
the door leads to a cycle of securing construction permits, digging
and trenching streets, and disrupting traffic. The results are high
costs and long provisioning times to businesses that need the band-
width. To resolve the connection needs of a customer to access the
Internet, the wireless optical networks provide the connection as
shown in Figure 10-18. Here the wireless optical networks provide
native LAN speeds to the Internet in a shorter provisioning time and
at a more reasonable cost.
Changes occurred since the original publication that discussed the
free space operation. First, significant improvements have resulted
from the use of free space optics using infrared lasers and transmit-
ting up to 155 Mbps at a distance of just under two miles. This is
shown in Figure 10-19. A few companies were in the business at the
time. However, many newer ones have seen the opportunity to jump
into the business quickly and gain access to the customer’s door
around the local ILEC/CLEC twisted pair wires. The benefit here is
that the frequencies used are in light and are not regulated or
licensed in any way.This means that as long as we have line of sight,
we can install. The disadvantage is the limited distances and the
limit of line of sight. The other advantage is that these systems are
becoming very reasonable to install for an OC-3 throughput for short
distances.