Information Technology Reference
In-Depth Information
The “duplex” pattern shown is technically not allowed by TIA-568-B, which
only lets you use one “service” per cable. In some circumstances, duplexing the
cable will work just fine for low-speed data or possibly data/voice combinations.
Duplexing may limit your distances and may preclude 100 Mbps operation. But,
you should use this “work around” cautiously and either run a new cable or install
a small hub as soon as you can.
Problems in 10/100BaseT usually relate to individual workstations. If you are
having a problem, the hub status lights can diagnose total failures of the cable to a
workstation or server. Common cable failures include damaged wires, connectors
pulled loose or not properly seated, and poor or improper connections to the mod-
ular plug. Use only the expensive, tool-and-die type crimp tools for 8-pin plugs. The
cheaper tools will not properly seat the center contacts on the plug and the cable
may fail. In addition, you should be very cautious if you use solid wire with modu-
lar plugs (see Chapter 9 for more information). If the cable tests well, suspect the
workstation's network adapter, if the problem is with a single workstation. If all
workstations are affected, suspect the hub or any thinnet or thicknet connections
between hubs or to other devices.
100BaseT Cabling Issues
Standards for 100 Mbps
Fast Ethernet
networks have evolved rapidly. Many pro-
prietary methods and interim standards were put forward since 10BaseT was first
introduced. The IEEE 802 standards committee resolved the competing technologies
with a supplement that details the implementation of 100BaseT. There are two cop-
per wire 100BaseT variations under what is known as the IEEE 802.3u Supplement
standard. They are 100BaseTX and 100BaseT4. A companion 100BaseFx (covered
later in this chapter) rounds out the 100 Mbps CSMA/CD standard offering. The
non-CSMA/CD 100VG-AnyLAN (described in the Appendix) was relegated to a
new committee, IEEE 802.12, after much debate.
In some ways, the new standards encompass several formerly proprietary tech-
nologies under the same standards umbrella. The variations are not cross-compati-
ble, although some vendors may offer adapters or hubs that can meet more than one
standard. You should still be cautious in what you get, as the product nomenclature
can be quite ambiguous.
These 100 Mbps Ethernet topologies are sometimes referred to as Fast
Ethernet. The implementations of the two main standards, TX and T4, differ in the
minimum link performance category and the number of pairs required. The impor-
tant point is that either of the copper Fast Ethernet standards can be supported on
an unmodified TIA/EIA-568-C cabling system, although the required category of
