Twisted Pair Cable

Twisted Pair Networking offers full twisted pair networking services. The core of these services is the twisted pair cable. This page will attempt to cover some twisted pair cable basics. Note that some cabling specifics such as length, impedence, and available bandwidth are dependent on the application, not the assembly of the cable.

The RJ's

"RJ" defines the type of "jack" or connector at the end of a cable, or the connector into which a cable is inserted. Typical telephone installations use RJ-11 (4 wire) or RJ-14 (6 wire) connections. Typical network installation use RJ-45 (8 wire) connections.

The Cable

One major, and easily recognizable difference between telephone and network cable is that telephone cable is not twisted, while network cable is. Twisting a cable can allow for electronic noise to be reduced and even eliminated from the line. Telephone systems are not operating at a frequency high enough to demand that kind of electronic consideration.

The Colors

There are two standards for twisted pair cable ends. Whether used at the patch panel, in a wall jack, or at the ends of a cable, there's only two standard ways to make the cables. Using the standards allows anyone who follows to understand what you've done.

The images to the left and below show the pairs as represented in a wall jack or on a cable end. Although it's difficult to tell from the graphics, imagine that you're holding the cable in your hand, and about to plug it in.

If you're imagining you're looking at a wall jack, it'd be as you're looking at it mounted on the wall, waiting to take a cable; pin 1 is always on the left. Of course, this assumes that the jack is mounted such that the "key" on the cable end is on the bottom (as in the illustration).

If you're looking at the cable, the "top" of the cable end would be the side with the contacts on it, making the bottom the part with the key. Looking at the top of the cable end, the middle pair is always blue, and the rightmost pair is always brown. The cable colors listed in the chart below are from left to right as you go down the list.

T586A			T586B
	Pin	Color		Pin	Color
	1	White/Green		1	White/Orange
	2	Green		2	Orange
	3	White/Orange		3	White/Green
	4	Blue		4	Blue
	5	White/Blue		5	White/Blue
	6	Orange		6	Green
	7	White/Brown		7	White/Brown
	8	Brown		8	Brown

Note the significant difference is the reversal of the Orange and Green pairs. This simply changes pairs 2 and 3. T586B is most popular, and is probably the kind best used in most environments.

MATCH THE ENDS

It is of the utmost importance that you use the same "pattern" on both ends of the cable. If the cable ends don't match, communications will likely fail! There are a couple of exceptions, as noted below.

To help make things easy, most manufacturers of wall-plate assemblies and patch panels provide color guides on their devices. In those cases, simply follow the color guide. Sometimes, however, the color guide is a little confusing, in those cases, simply connect the "white and color" first.

Patch Panel Example

An example of a typical T568B patch panel color guide is shown below. On the patch panel, you're expected to punch down the appropriate colored cable in the white portion of the example. Of course, on your patch panel there'd be a slot to receive the cable instead of an empty white box...

Given this example, the wires would go in White/Blue, Blue, White/Orange, Orange, White/Green, Green, White Brown, and finally Brown.

Straight-Through Cable

Twisted pair networking is designed to connect network devices (computers, printers, etc.) to hubs, not to each other. The network hubs provide the necessary "crossing over" from the transmit and receive wires, as well as (in some hubs) buffering, collision control, power amplification, and packet switching.

A straight-through cable is used to connect a device to a hub. Quite simply, the cables on one end must match the cables on the other end; that is, whatever is on pin 1 on one end must be on pin 1 on the other end. Ethernet networking does not use all eight wires in a RJ-45 cable. However, it is recommended to use only Category 3 or higher, and connect all 8 wires.

Note the colors have been left out, although you can see the "color" and "color/white" are represented to show how important it is to keep the pairs together.

Cross-over Cable

Twisted pair networking can be used without a hub to connect two, and only two, devices. A common use for this is to connect two computers with Ethernet cards together, or to connect network hubs without cross-over interfaces. When using a cross-over cable without a network management device (such as a network hub), an increase in collisions may occur. The only real disadvantages of using a cross-over cable versus a straight through cable and hub is the lack of ability to add additional network devices, and a lack of electronic isolation.

Note the colors have been left out, although you can see the "color" and "color/white" are represented to show how important it is to keep the pairs together.