Information Technology Reference
In-Depth Information
field termination that might have excessive untwist or other problems. The patch
cords would hopefully be factory terminated, carefully inspected, and certified.
With cross-connection, you add four points for potential workmanship problems:
the connecting block, the two end connections of the cross-connect jumper, and the
multicircuit termination leading to the hub.
Which is right for you? That may depend on the size of your facility and the
training of LAN maintenance personnel. The patchless approach should probably
be avoided in TRs having under 100 to 200 connections, unless you have trained
people with the ability to do complex wire tracing and the workmanship skills to
make high-quality connections.
Fiber-Optic Termination
Fiber-optic cables are treated a little differently in the TR than are conventional
metallic cables. However, the concepts are the same. Basically, in the telecommuni-
cations room, cables from the horizontal distribution to work areas are all brought
together in some fixed, orderly arrangement for interconnection to network hubs
and other equipment. Fiber-optic cables may be used for the horizontal cabling, in
place of traditional metallic wire. Fiber-optic cables are also widely used for the
backbone cabling that runs between TRs. Differences in the TR terminations for
fiber-optic cables exist because of the nature of the signals (light) and the fact that
the transmission medium (glass fiber) requires special handling. These differences
limit the number of ways the cables may be terminated, severely limit routing and
handling considerations, and cause fundamental differences in the structure of
patch panels.
In addition, fiber-optic connections have what might be called “polarity.”
Because a single fiber sends its signal in only one direction, a fiber-optic link always
requires two fiber connections, one to transmit the signal in each direction. To oper-
ate properly, the transmitted signal from one end must connect to the receiver port
at the other end, and vice versa. This is called a crossover connection.
In contrast, metallic cable link standards use straight-through wiring for most
connections. This is accomplished by defining two types of equipment interfaces,
such as the DTE and DCE interfaces of RS-232 that are meant to connect “termi-
nal” and “communication” devices. The same type of pattern exists in
10/100/1000BaseT (adapter versus hub) and AUI (repeater versus transceiver).
However, the fiber-optic equipment interfaces have traditionally been identical, pro-
viding signal identification only by the label beside each of the two fiber-optic con-
nectors. That means that the user/installer must provide fiber cabling that
accomplishes the crossover.
Search WWH ::




Custom Search