CROSS & PATCH CABLE

Ethernet Cables - RJ45/Colors & Crossover - Illustration

CROSS CABLE

10-Base-T Crossover Cable

The following figure shows the correct wiring for a 10Base-T crossover cable (assuming you're using RJ-45 connectors).

This cable can be used to connect two computers together without a hub, or to connect two hubs together (without using an uplink port). If you're connecting two hubs together and one of them has an uplink port, use a straight cable (rather than the crossover) to connect the uplink port of one hub to one of the (non-uplink) ports of the other hub.

A bit of technical background: Most computer and workstation network adapter cards have interface ports referred to as MDI ports (RJ-45 pin assignments shown on the left side of the above drawing). "Uplink" ports on hubs have the same pin assignments. Most normal ports on hubs have MDI-X ports, which use pins 1 and 2 for receive, and pins 3 and 6 for transmit. A straight cable (one that connects pin 1 to pin 1, pin 2 to pin 2, etc.) can be used to connect an MDI port (a computer) to and MDI-X port (a normal port on a hub). Obviously, to connect two MDI ports together, it is necessary to connect pin 1 to pin 3, pin 2 to pin 6, and so forth.

RG 45

RJ-45

The RJ-45 connector is commonly used for network cabling and for telephony applications. It's also used for serial connections in special cases. Here's a look at it:

Also, please note that it is very important that a single pair be used for pins 3 and 6. If one conductor from one pair is used for pin 3 and a conductor from another pair is used for pin 6, performance will degrade. See the following figure.

To learn more about Ethernet, check out Charles Spurgeon's Ethernet Reference.

RJ-45 Pinout for RocketPort

The following chart shows the pinout for RJ-45 connectors used on certain RocketPort serial interface cards (manufactured by Comtrol).

Pin	Name/Description
1	Request To Send
2	Data Terminal Ready
3	Ground
4	Transmit Data
5	Receive Data
6	Data Carrier Detect
7	Data Set Ready
8	Clear To Send

Pinouts for ISDN

Here's an ISDN BRI U port pinout for a Cisco 750 series router:

Pin	Function
1	Not used
2	Not used
3	Not used
4	U interface network connection (tip)
5	U interface network connection (ring)
6	Not used
7	Power (pass-through to S connector)
8	Ground (pass-through to S connector)

The following chart shows the pinout for RJ-45 connectors used on certain ISDN S/T interfaces. For more info, see ANSI T1.605.

RJ-45 wiring for Ethernet (T568B standard)

Pin	Color	Name/Description
1	White/Orange	N/A
2	Orange	N/A
3	White/Green	Receive+
4	Blue	Transmit +
5	White/Blue	Transmit -
6	Green	Receive -
7	White/Brown	-48VDC (optional)
8	Brown	-48VDC Return (optional)