Information Technology Reference
In-Depth Information
terns. As we said, hub connections often use only two pairs per port (four wires) to
minimize the number of ports per connector.
Here is an example of the problem of connection mapping. Let's say you intend
to install a 10/100BaseT network using hubs with multicircuit connectors instead of
single port jacks. Such hubs typically use a card rack with plug-in cards. You will
run cables from your hub cards to a patch panel to fan out the individual ports to
modular jacks. Naturally, you will want the 8-pin modular jacks on the patch to
have the same pinouts as a standard 8-pin modular jack on a hub with individual
connectors.
A standard 10/100BaseT modular hub jack defines pin 1 as transmit
, pin 2
as transmit
. A multicircuit hub con-
nector could assign eight pins to each port, but only four pins are needed for
10/100BaseT, so assigning four pins per port achieves twice the density on the con-
nector. For our example, let's say that your hub card connector assigns four pins per
port, representing two pairs of the multiconductor cable. This gives you a total of
twelve 10/100BaseT ports per 50-pin connector. The cable connects between the
hub card and the patch.
Now, let's look at the way the ports are mapped from the 50-pin connector to
each modular jack on the patch panel. Standard 10/100BaseT uses four pins of the
8-pin jack. These four pins correspond to two of the regular 4-pair groupings of the
jack, pairs 2 and 3. Remember that T568A and B simply reverse the order of these
two pairs.
The “first” pair for each of the ports on the 50-pin connector usually corre-
sponds to “transmit
, pin 3 as receive
, and pin 4 as receive
/-”. Now, here is the mapping part: the transmit
/- pair
must connect to pins 1 and 2 on the 8-pin jack, while the receive
/- goes to Pins 3
and 6, for proper 10/100BaseT connectivity. If the patch uses the T568B pattern to
connect the patch jack, the transmit and receive pairs will appear on the proper pins.
But if the patch is wired for the T568A pattern, the two pairs will be in reverse order
and the connection will not work (unless the pair order on the 50-pin connector has
also been reversed—a rare circumstance because the TIA recognizes only the stan-
dard color code pattern for that connector, not a pair order).
This is one place where the TIA's preferred T568A pattern will get you into
trouble. Note, however, that all of your modular patch cords, horizontal cable patch
panels, and workstation outlet jacks can still use the A pattern. The rule is that both
ends of a connection must be the same, whether that connection is a horizontal
cable, a patch cord, or (yes) a patch panel fan-out of a multicircuit hub port. Always
ensure that you match the LAN connections on the hub card's connector with the
connector-to-jack mapping on the patch panel so that the correct LAN signals will
be on the pins of the patch panel jacks.
