UTP Connections using RJ-45 Description

RJ-45 Connector

RJ(registered jack) is a standard physical network interface which is used for connecting telecommunications or networking equipments. RJ-45 is the most widely used connector. Eight colored wires can be connected to the connectors pins. The wires are twisted into four pairs. Two pairs carry the voltage and are called  tip and the other two are grounded and are called ring. The connector is crimped onto the end of the wire using a crimping tool. The pin locations of the connectors are numbered from the left 8 to 1.

                                          Pin        Wire Pair

                                           1          Pair 2 T2

                                           2          Pair 2 R2

                                           3          Pair 3 T3

                                           4          Pair 1 R1

                                           5          Pair 1 T1

                                           6          Pair 3 R3

                                           7          Pair 4 T4

                                           8          Pair 4 R4

Note : T denotes  "Tip" and R denotes "Ring"

Two type of connections are made using UTP and Rj-45 which are

1. Straight through
2. Crossover

Straight Through

In straight through cable the wire on both cable ends are in the same order. Consider a Switch at one end and a router on the other.

                                       Switch                                        Router

  Pin        Label                                         Pin       Label

   1          RD+   <------------------               1         TD+

   2          RD-    <------------------               2         TD-

    3          TD+     ------------------>              3         RD+

    4          NC                                             4          NC

    5          NC                                             5          NC

     6          TD-    ------------------ >               6          RD-

    7          NC                                             7          NC

    8          NC                                             8          NC

Straight through wires are used to connect different devices as i have told in the early post.

Crossover

In crossover the wires on each end of the cable are crossed. Now consider two switches on both ends.

          Router 1                                   Router 2

  Pin        Label                             Pin       Label

   1          RD+                                 1         TD+

   2          RD-                                  2         TD-

   3          TD+                                 3          RD+

   4          NC                                   4          NC

   5          NC                                   5          NC

   6          TD-                                  6          RD-

   7          NC                                   7          NC

   8          NC                                   8          NC
 
As i cannot make cross arrows so i am defining the position of the arrows below. You can make yourself in a paper

From router 2, the arrow is starting from pin 3 and is pointing to  pin 1 of router 1.
From router 2, the arrow is starting from pin 6 and is pointing to pin 2 of router 1.
From router 1, the arrow is starting from pin 3 and is pointing to pin 1 of router 2.
From router 2, the arrow is starting from pin 6 and is pointing to pin 2 of router 2.

Crossover connection are used to connect similar devices.