Ethernet Cabling and Pin Positions

• Document ID#: TEC_011
• Written: 01/12/98
• Last Updated: 08/13/98
• Author: JC & MF
• Product: Any Ethernet or Fast Ethernet product
• Description: Cabling Descriptions and Pin outs for Ethernet Networks (10BaseT or 100Base-TX)

Problem:
A common error when connecting a computer to a LAN is to make the connection with the widely available "silver satin" patch cable typically used to connect telephones to a telephone jack. The problem is that this silver satin patch cable used for telephones does not have twisted pair wires in it. This lack of twisted pairs results in excessive signal crosstalk and can cause "phantom collisions." This occurs because collisions are detected in twisted-pair Ethernet by the simultaneous occurrence of signals on the transmit and receive wire pairs. Excessive crosstalk signals can look like simultaneous traffic and can falsely trigger the collision detection circuit. Thus, it is important to identify the type of wire you have.

10BaseT network installations require a minimum of Category 3 UTP (Unshielded Twisted Pair) wire. If you are installing new wiring in your building, we recommend that you install Category 5 UTP wiring. This will save you the trouble of running new wiring in the event you choose to run 100BaseTX in the future. Note: 10BaseT and 100Base-TX both use the same pin out standard.

Situation:
The 10BaseT system operates over two pairs of wires; one pair used for Receive Data signals and the other pair used for Transmit Data signals. If you are planning to install a 10BaseT or 100BaseTX network you need to find out what wiring to use.

Here are some descriptions of the categories of wire, the twists per foot, and the colors of wire that one might encounter:

Categories:

• Category 3 - solid copper, specified for up to 16 MHz. Typically used for voice and data transmission rates up to 10 Mbps.

• Category 4 - solid copper, specified for up to 20 MHz. Intended for extended distance medium-speed LANs up to 16 Mbps.

• Category 5 - solid copper, specified for up to 100 MHz. Intended for high-speed (100 Mbps) networks.

The number of twists per foot is very important. In commercial wire you will see anywhere from 2 to 22 twists per foot. On good data grade cable you will typically see 12-22 twists per foot. Several factors determine the number of twists including, alloy type, how the twisted pairs are laid together inside the insulation, and dB signal loss characteristics of the materials. All of these fundamentally relate to how well the cable handles high frequency signals.

Wiring Colors and Signals:

The transmit data (TD) and receive data (RD) signals on each pair of a 10BaseT segment are polarized, with one wire of each signal pair carrying the positive (+) signal, and the other carrying the negative (-) signal. Colors may vary by manufacturer. This is just an example of what you might see.

RJ45 pin #	Color	Signal
1	white/orange	TD+
2	orange	TD-
3	white/green	RD+
4	white/blue	Unused
5	blue	Unused
6	green	RD-
7	white/brown	Unused
8	brown	Unused

Solution:
Identify the type of wire that you have installed between nodes on your 10BaseT hub or the next EtherWave device in a daisy-chain. Looking at the outside sheath on the wire you should be able to read some lettering that will tell you the type or category of the wire. You can usually determine that a pair of wires form a twisted pair by the coloring of the wires. A wire with the color orange/white is paired with the white/orange wire. In some cases, like the example above, one of the wires may be a solid color: i.e. green will be paired with the white wire that has a green stripe (white/green).

A normal 10BaseT or 100BaseTX cable:
1 <--> 1 \
2 <--> 2 / 1 & 2 must be a twisted pair

3 <--> 3 \
6 <--> 6 / 3 & 6 must be a twisted pair

The numbers refer to the position in the eight-position RJ-45 connector. These positions are numbered from left to right when you are holding the connector pointing up, as if you were about to plug it into the ceiling, with the plastic clip away from you.

Note: 100BaseTX uses the same pin positions, but requires Category 5 cable.

Distance limits: You can have nodes up to 100 meters (328 feet) from a 10BaseT or 100BaseTX hub.

For information about cross-over cables, see: TEC_012 Cross Over Cable Pin-outs.