Wireless LANs - LAN Wiring - page 342

Then, you must configure the AP, usually through an RS-232 or Ethernet con-
nection to a computer. You may be able to configure the AP wirelessly, from your
laptop PC, but in any event, be sure to change the administrator password on the
AP after you have it up and running.
The process of installing a simple AP used to be somewhat complicated, requir-
ing special training for the installer. However, most of the latest wireless kits come
with the proper driver software and good setup programs to make the process really
easy. Don't be fooled. The “default” setup of these kits will leave your wireless and
wired computer network helplessly undefended against even amateur intruders. You
need to change default passwords, enable encryption, and possibly create an access-
control list of permitted MAC addresses for the client PCs that you want to have
access to your network. In addition, you may need to properly configure IP
addresses, WiFi channels, and, in some cases, network names (SSIDs) on both the
AP and the W-NICs to get everything to work right (or at all).
This process can be fairly involved, and you may want to consult Build Your
Own Wireless LAN , by James Trulove, for more information.
Power over Ethernet (PoE) for APs
A relatively new innovation called DTE Power , or Power over Ethernet , adds the
capability of providing electrical power to data terminal equipment (DTE) over the
same cable that provides the data connection. The IEEE 802.3af-2003 Amendment:
Data Terminal Equipment (DTE) Power via Media Dependent Interface covers the
subject completely. (Don't you just love their names for this stuff?)
This is not a new idea, really. In fact, we have been doing power-over-the-sig-
nal-cable for some time in the CATV and phone business. You can easily provide
power to an amplifier or a satellite downconverter over the same coaxial cable that
carries the signal.
For that matter, T1 repeaters and voice “line extenders” can use “span power”
over phone lines, instead of DC converters. And, that plain-old telephone you are used
to is probably powered by -48v DC on the same pair you talk on. However, circuit
power is a new innovation for high-speed data networking cables, and standards had
to be developed to cover everything from the pin numbers to the voltage and current.
There are two ways to provide PoE, as it is called. The first way is to “phan-
tom power” the line by using special transformers to inject and recover the power
from the LAN cable. The transformers are used to electrically isolate the phantom
voltage from the balanced pair, by creating a potential difference (voltage) between
pairs. Carefully done, the balanced transmitters and receivers of the data interface
never know what's happening. Part of the PoE operation informs the connected