Information Technology Reference
In-Depth Information
The connector module includes the modular connector jack and the terminal
mechanism for connecting the cable. Termination is accomplished by several types
of IDC connectors, as we will describe later. The construction of the connector/ter-
mination module generally produces much lower noise and crosstalk than with con-
ventional fixed jack plates.
For this reason, these jacks are preferred for LAN wiring, even in a Category
3 installation. They are also much easier and quicker to terminate than conventional
screw terminals. Notice we did not say that they were less expensive.
Another variety of jack plate is a two-piece modular jack assembly. These
assemblies are unique in that they separate the wire termination function completely
from the connector function. A typical two-piece assembly will include a backplate
module that the wire terminator snaps into after the cable is terminated. The termi-
nator module is essentially a special type of connector that mates with a printed cir-
cuit board-edge contact area. This arrangement is commonly called an
edge
connector.
The back module then mounts into the outlet box with the normal mount-
ing screws. To finish the assembly, one or more connector modules, each with a PC-
board edge contact, plug into the terminator module at the rear of the back module.
A faceplate is then attached to secure the connector modules in place. This type of
assembly has the unique feature that the front connectors may be changed without
reterminating the cable. For example, you could change from a single 8-position con-
nector to a dual 8-position one, or change to a 6-position or even coax module.
Of course fiber connectors are out, because it is cable that is terminated, not
fiber. Figure 6.9 shows an example of a two-piece modular jack assembly.
Modular jacks are often referred to as “RJ-45” jacks. This is not really the cor-
rect moniker, although it is in very common use. Because all modern LAN wiring
uses the 8-pin (8-position, 8-conductor) modular plug and jack, we will call these
conductors “8-pin modular” or just “modular.” For a more complete discussion, see
the box “RJ-45, What's in a Name” in Chapter 9.
Termination Types
Two basic types of wire termination are used with modular jacks for twisted-pair
wire. These are the screw terminal and the insulation-displacement connector (IDC).
The screw termination is the original type that was used with telephone systems. It
is still found in some LAN wiring installations, but is not recommended for
Category 4 or 5 operation and certainly not Category 5e or 6. As a matter of fact,
you probably will never see screw-terminal connectors certified above Category 3,
if they are certified at all. You definitely do get a better connection, from the view-
point of LAN transmission, with the other type of termination.
