What Do You Know About Registered
Jacks?
All about those RJ connectors used
in business telephone and computer networking.
You're no doubt quite familiar with the
terms RJ11, RJ45 and perhaps RJ48. You'll immediate recognize
them as the connectors used for telephone and networking equipment.
But do you realize that these aren't mere catalog numbers or
even de facto industry standards. They are part of a official
telecommunications standard in the Code of Federal Regulations
established by the FCC. They're not just connector jacks, they're
Registered Jacks.
What is a Registered Jack?
Registered Jacks is where the initials RJ come from. There are
numerous RJ types, but you are only likely to run into a few
of them. Each RJxx was established by a USOC or Universal Service
Order Code under the Bell Telephone System. The code specifies
the jack, the plug and the wiring scheme. There is also a suffix
letter, such as C for flush mount or surface mount. Other letters
include W for wall mount, S for single line, M for multi-line,
and X for complex jack.
Let's take a look at some of the more popular
Registered Jacks. RJ11 is the one familiar to both consumers
and businesses. It is the interface used for single line analog
telephones. A phone, computer or modem will likely have a RJ11C
jack unless there is a hardwired lead and plug attached directly
to the device. In the kitchen, a RJ11W is a wall mount jack that
will both connect and hold a telephone set.
T1 Smart Jacks
T1 lines are terminated in "smart jacks" at the demarcation
point, usually in the telephone closet of the business. The smart
jack acts as a network interface to protect the line. The user
interface is most often a RJ-48C connector. This registered jack
describes an 8 position jack with four active wires, one pair
for transmit and one pair for receive. Two pins are assigned
for cable shield integrity and two are reserved for future use.
Another T1 line connector that is used
less today than in years past is the RJ48X. The "X"
means complex jack. In this case it refers to shorting bars that
connect the transmit to the receive pairs when no plug is inserted
into the jack. The reason this is done is to loop-back the signal
for testing purposes.
What's called an RJ45 connector today looks
much like an RJ48, but the RJ48 is more specialized in that it
has a keyed connector and a notched jack. A RJ45 cord will plug
into a RJ48 jack, but not the other way around.
The Story Behind The RJ45 Standard
The ubiquitous RJ45 connector system that is so popular in networking
connections today is actually somewhat different than the original
RJ45 Registered Jack specified by the telephone company. The
original RJ45 was a keyed connector that used two pins for signal
and two for a programming resistor. This connector system is
rarely seen today but the RJ45 naming convention has been adopted
for a similar size connector used almost universally in Ethernet
twisted pair cabling.
The correct nomenclature for the RJ45 connector
we use today is an 8P8C modular connector. The 8P8C stands for
8 positions, eight conductors. In other words, all pins are connected.
The wiring scheme follows one of two Electronic Industry Association
standards, either T568A or T568B. T568B is equivalent to the
old AT&T 258A standard, but T568A is preferred for new installations.
Both standards use all 8 pins but are wired differently. Within
a particular physical plant, one standard or the other is implemented.
Mixing the two can cause problems with pairs being swapped at
different ends of a wiring run.
How to Get Support for Your Wiring Project
Now you know about Registered Jacks. Well, at least a brief introduction
to the subject. If your business has a need for telephone or
computer networking cable installation or upgrades, The VAR Network
offers an easy way to find
qualified suppliers anxious to discuss your project and offer
competitive bids.
Want a Better Deal on T1 Voice or Data
Lines?
Does your company use T1 PBX telephone,
point to point data transfer or dedicated Internet lines? Our
Shop For T1 service may be able to offer you a better price right
now. Simply fill out the form below to see instant pricing on
most services. Or call toll free 1-866-436-7868 Ref. # 1265
to talk to our technical consultants about your business needs
and receive customized proposals.
