Information Technology Reference
In-Depth Information
This common usage error would matter very little if you were never
going to use high-speed data networks. However, the TIA-568-C version of
the 8-pin modular connector interface has very specific performance
requirements that may not be met by the generic nonrated connector that
simply goes by the RJ-45 name. It would have been convenient if the TIA
had given this connector a new name commensurate with its specifications.
Perhaps it could have been called the “T568-8/Cat5e” connector, or how
about just “T568-RJ” to borrow from both the past and the present.
When will people stop calling it an “RJ-45”? Don't hold your breath!
Don't grit your teeth either! Just get used to thinking that a very special type
of connector is meant when a “RJ-45” is used in your LAN wiring system.
And, oh yes, never ever use the “RJ” word on the 'net!
who call the connectors “RJ-45s,” however wrong the term might be.
The 8-pin modular plug that is used in standard LAN wiring is specified by IEC
603-7, “detailed specification for connectors, 8-way, including fixed and free con-
nectors with common mating features.” This is the plug that is specified in TIA-568-
C and related documents, and in ISO/IEC IS-11801.
Modular connectors are primarily intended for terminating cables with
stranded conductors. In fact, the original connector was designed to terminate a flat
cable containing from two to eight stranded conductors.
It was also designed primarily for the audio frequencies of telephone lines,
although the connector is officially rated for use up to 3 MHz. Unfortunately, the
industry not only uses the connector at frequencies far above that, but also needs to
place twisted-pair conductors, encased in a round cable jacket, into the modular
plug. To allow the use of the modular connector at LAN frequencies from 10 to 100
MHz, the TIA has simply specified performance criteria (primarily attenuation and
NEXT) that the connector must meet. As long as these criteria are met, the connec-
tor can be used in applications up to Category 5e.
The Category 6 plugs and jacks, while physically compatible with their
Category 5e cousins, are specially configured to reduce near-end crosstalk (NEXT)
when mated. This electrical compensation can actually cause a link failure when
Category 6 connectors are mated to Category 5e connectors.
Modular connectors are available for solid wire, although some authorities dis-
courage using solid wire for cords, even with these special connectors. The differ-
ence between the two connector designs is shown in Fig. 9.1. As you can see, the
modular pin is a flat contact with a pointed end that pierces through the insulation
of the wire and makes electrical contact with the stranded wires. The contact may
