Information Technology Reference
In-Depth Information
looking at the plug end. A properly crimped plug will have all eight contacts fully
engaged and even on the tops, which will be very slightly below the plastic channels
between the contact pins. An improperly crimped plug will show a distinct rounding
upward of the center contacts. Side-action crimp tools may favor the contacts on one
side of the plug. The plug should also be inspected from the front and top to ensure
that the contacts have not drifted to the side, as can happen with inexpensive modu-
lar plugs. As simple as these plugs are, there are still significant differences in quality.
It would not be proper in a discussion of LAN cable terminations to ignore the
problems that result from the choice of the classic 8-pin modular plug and its mat-
ing jack as the standard UTP connector. These components are responsible for the
majority of limitations with this generation of high-speed networking. The connec-
tor, as stated before, was designed for frequencies well below 3 MHz, and it has very
poor characteristics at frequencies approaching 100 MHz. The NEXT performance
of the plug and jack is so bad at 100 MHz that you will see few manufacturers quote
performance margins that exceed the TIA performance standards by more than 1 or
2 dB, if they quote a margin at all. Test equipment manufacturers even create spe-
cialized low-NEXT adapters or digital processing techniques to compensate for the
performance deficiencies of the modular connector in their own test equipment.
Nevertheless, with quality materials, proper assembly procedures, careful
workmanship, and proper testing, the modular connector can support the highest
performance metallic cable networks in wide use today.
User cords are the final connection step in a LAN wiring system. They are the cables
that connect between the installed universal wiring system and the network equip-
ment. They exist on both ends of a link, at the work area and in the wiring closet.
In most modern LAN installations, the telecommunications room will contain
wiring hubs that consolidate all the station cables into a contiguous network.
Telecommunications rooms that contain network equipment in the form of hubs,
repeaters, and servers are also “equipment rooms,” which add a few requirements
over and above those for a simple telecommunications room, but we will just call
them telecommunications rooms to keep things simple.
User cords include workstation cords and equipment cords. Technically, user
cords do not include patch cords, which are part of the horizontal cross-connect.
Sometimes all modular cords are called patch cords, regardless of their function, but
we will make a distinction between true patch cords and user cords. Patch cords,
which were covered in the last chapter, are essentially the same as user cords, except
for length and color.
