Information Technology Reference
In-Depth Information
because of extended testing and greater marginal performance over the minimums
required by the performance category. As is the case with jacketed pairs, consistency
in the geometry of the pair has a big influence on the transmission characteristics of
cross-connect wire. This means that pairs manufactured to very tight specifications
can produce a superior jumper that will have a very low return loss, indicating very
consistent impedance. This carefully controlled manufacturing also achieves better
performance in some of the other transmission parameters. You can indeed buy bet-
ter wire and cable, but you will probably pay more for the privilege.
Cross-Connect Routing and Marking
Cross-connect wires are routed between two termination points using the standoffs,
brackets, and other wire management devices that were described in Chapter 7.
Because of the lack of a jacket, cross-connect wiring will require a little extra care
in handling to maintain performance characteristics. Some of the standard practices
that are used in running telephone-grade cross-connects are not at all appropriate
for the higher performance categories of LAN wiring. For example, it is common
practice to sharply bend jumpers when they are wrapped around wire management
brackets and posts. These sharp bends may be less than the minimum bend radius
recommended in cabling standards such as TIA-568-C. This standard calls for a
bend radius to be not less than four times the diameter of the cable. Cross-connect
wire has no jacket, so its overall diameter is not as easily determined, but it is prob-
ably less than jacketed cable. It is certainly easier to bend, as the jacket imparts addi-
tional stiffness to regular cables.
Connections on wooden backboards are fairly easy to route. If you need addi-
tional routing paths, you simply add the appropriate brackets or standoffs to the
board. Wire is routed around or through the devices from start to end of a jumper.
Distant blocks or patches just require longer cross-connect jumpers. If you use con-
necting blocks or patch panels that are in separate relay racks, as may be the case
with large installations, you will probably need to route the wire up the side rail of
the rack, across a wiring tray to the other rack, and down the other side rail. Wire
management brackets, hangers, raceways, and trays are essential for proper protec-
tion and containment of the wire.
Cross-connects must be marked, just as with all other wiring components,
pathways, and cables. Obviously, the cross-connect wire itself is difficult to mark,
so you will have to ensure that the points of termination of the cross-connect are
marked clearly to indicate the identification of the cross-connect. The particular
type of connecting block that you use will make a big difference in your ability to
provide marking for each connection. Ideally, you would mark the termination in
