Technote: 10 Base-T Cabling
Source: South Hills DataComm and University of Minnesota
10 Base-T uses two pairs of wires: one pair for transmission and the second pair for receive. The physical connector commonly used is an 8 position modular plug, referred to as an RJ-45. All cables must be wired such that pins 1 & 2 are on one twisted pair and pins 3 & 6 are on a second pair.
There are two pinouts used: MDI for DTE devices (such as computers, printers, etc.) and MDI-X (hubs). Connecting an MDI port to an MDI-X port requires a straight through cable, and connecting either MDI to MDI or MDI-X to MDI-X requires a crossover cable. Pinouts of the MDI and MDI-X interfaces are shown below.
Note on pin numbers - when assigning pin numbers, plugs are as viewed from the end that the cable enters the jack. The latching tab is to the bottom and the contacts are on top. Pins are numbered starting from the left. Jacks are as viewed looking into the jack. The latching tab slot is to the bottom and the contacts are on top. Pins are numbered starting from the left. These conventions make the pin numbering the same on both plugs and jacks (i.e., pin 1 goes to pin 1).
There are several applications for crossover cables in 10 Base-T networks. The most common reason is to cascade hubs together in a tree topology. If both hubs have only MDI-X ports then a crossover cable is needed. Another application for a crossover cable is to connect two DTE devices together without a hub.
A standard 10 Base-T crossover cable wiring diagram is shown below.
Crossover Cable Pinout
In-Wall Wiring ConventionsHere is how all the wires should be connected in the wall and at junction boxes.
Last update: January 18, 1997