Information Technology Reference
In-Depth Information
Some manufacturers have products with extra features, such as modular snap-in
construction or fancy color inserts. Some even offer special 10- or 15-year war-
ranties if you use their cable, connectors, and certified installers.
Others offer separate wire termination and jack modules that plug together. In
many cases, the extra features will cost you extra money. You will have to judge the
benefit of these extra cost features for your situation.
In the other sections of this topic, we will try to point out the cost trade-offs
of the devices that are described. You should be aware that any time a connector,
cable, or other wiring device is referred to as “easier to use” or “flexible,” there
might be cost implications. Remember too that your goal is not necessarily to spec-
ify or install the cheapest wiring solution, but to find the balance among features,
cost, and reliability that meets both your current and planned future needs.
Mixing Data and Telephone
Combining conventional analog or digital telephone signals with data on different
pairs of the same cable is sometimes a consideration for cost savings and efficiency.
This so-called mixed media approach is an option that may work fine in a lower-
speed network environment, such as 10BaseT or Token-Ring, but it may be fraught
with problems at higher 100 to 1000 Mbps LAN speeds. (At the least, there are lots
of “ifs.”) If your telephones are analog, your LAN speed is conventional, and the
telephone cross-connect is in the same TR as the LAN hubs, then you probably
could use the same cable for data and phone very successfully. This case assumes
that you are using at least Category 3 cable, the minimum data grade, and that the
cable runs are not too close to the 90 m maximum.
However, if your telephones are digital, or you intend to use 100 or 1000 Mbps
LAN data, or you are installing the LAN hubs in a separate TR from the telephone
interconnects, then you should run two separate cables for data and voice (even if
your voice is VoIP). For that matter, if you know that the telephone installers are apt
to be overly creative around the LAN wiring, you should run separate cables (color-
coded for added protection). Table 1.1 shows some of the typical recommendations
for telephone and data.
The reason for the concern for mixing voice and data is the phenomenon of
crosstalk that occurs between pairs of the same cable. The higher frequency compo-
nents of 100/1000 Mbps LAN signals, along with their greater attenuation per foot
of cable run, make them much more susceptible to interference from other sources.
Such sources clearly include digital telephones and other LAN signals. Even mag-
netic fields from fluorescent light fixtures can cause problems. At cable run distances
that approach the maximum limit, these LAN signals are significantly more suscep-
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