Information Technology Reference
In-Depth Information
cards so they can connect between two wired LANs on either side and, in addition,
to two wireless networks on either side of the link.
For outdoor LAN-to-LAN operation, use directional gain antennas. If you are
strictly point-to-point, which means only two end points, you can use directional
antennas at both bridges. Highly directional antennas are available to give you a
range of 10 to 20 km. You will need Yagi or even parabolic antennas to achieve this
range, and you must still have optical line of sight.
If you want to go point to multipoint, you will use an omnidirectional antenna
at the main site, and directional antennas at the remote sites. These directional
antennas will be pointed at the main site, as before. The range will be reduced,
because the central omnidirectional antenna will not have as high a gain as the
directional antenna used in the point-to-point case. However, coverage will still be
excellent. Line of sight is required, as before. This mode of operation is suitable for
a small campus connection to several buildings or even a connection between users
and an Internet service provider.
New options are available at data rates beyond 11 Mbps, to 54 MHz and
above. We have covered WLAN operation here. However, operation of wireless
connections for non-LAN traffic is also possible with special hardware. For exam-
ple, wireless devices are available to interconnect buildings at 56 kbps, T1, DS3, and
OC-3 rates. In fact, all of the older microwave links used these rates, but they
required special licensing and siting, and were intended for long intercity links.
Our WLAN operation, on the other hand, uses unlicensed frequency bands,
lower power, and shorter distances.
All computer systems periodically require maintenance and repair. If you think of
the wireless network as just another computer system, you can use the same tech-
niques to troubleshoot and repair these networks.
We prefer a step-by-step approach that separates the overall system into each
component part. We then determine which subset of component parts could be
causing the symptoms we see. Then, through an orderly process of elimination and
substitution, we isolate the component that has failed and make a repair.
Determine the Scope
First in this process is to determine specifically how much of the network is
affected by the problem. In the case of the wireless network, we are frequently
