Information Technology Reference
In-Depth Information
wall outlet, and that you have preserved the pair order during punchdown and
cross-connect. See Chapter 8 on patch panels for more details on the internal wiring
pattern of a patch panel.
The official stance of the TIA is that the A pattern is preferred. That statement
certainly applies to new installations, since it would be problematic to switch the
pattern in an older installation. You could also justifiably choose the B pattern if
Avaya/Lucent (AT&T) components are used, since that is their standard offering.
There is great debate over which pattern is used the most. The truth is in the hear-
ing. The customary pattern varies widely, depending upon whom you ask and what
part of the country (or the world) you live in. However, it seems that the A pattern
originally was not used as much because it was different from the pattern that had
historically been required for telephone use. Now that most manufacturers offer
both, you are free to follow the TIA's preference, or yours.
What happens if you use one pattern on one end of a cable run and another on
the other end? Most LAN network connections will fail, and telephone connections
that require two pairs will also fail. Pairs 2 or 3 are used by almost every device we
connect to an 8-pin modular jack.
The TIA wiring patterns are considered universal in that they are applicable
to several types of connections, because they cover all eight pins of the modular
connector. For example, the TIA patterns can be used for any of the Ethernet
connections, such as 10 and 100BaseT. The TX and T4 variations are both han-
dled, as are 100VG-AnyLAN, 1000BaseT(4), and 1000BaseTX, since all four
pairs are specified. In addition, the TIA patterns can support Token-Ring,
ARCnet, ISDN, T1, ATM-PMD variations, and, of course, telephone wiring in
its many variations.
You can make a very good argument that the TIA-568-C wiring system is as
close to a universal wiring system as we will ever get. Of course, there will always
be situations that do not fit this standard model, but more and more equipment is
being designed to take advantage of its characteristics. If you choose to diverge from
the standard, to implement some of the 2-pair technologies, for example, you may
be left out in the cold in a very short time. For example, the only practical way to
increase data rates on unshielded twisted-pair wiring beyond the current 1000 Mbps
data rates is to use additional pairs in a multiplexing or encoding scheme. This
means that you can go to 1000 Mbps data rates without having to replace installed
Category 5e cable links, which are nominally rated to 100 MHz. However, these
technologies need all four pairs. You cannot very well use four pairs if you decided
to wire just two, just to save a little money in the short term. It is therefore strongly
recommended that any new installations adhere very closely to the TIA standards,
including the number of pairs to each outlet jack.
