Typically, when connecting different types of devices, use a straight-through cable. And when connecting the same type of device, use a crossover cable.
1. Straight-through UTP Cables
A straight-through cable has connectors on each end that are terminated the same in accordance with either the T568A or T568B standards.
Identifying the cable standard used allows you to determine if you have the right cable for the job. More importantly, it is a common practice to use the same color codes throughout the LAN for consistency in documentation.
Use straight-through cables for the following connections:
- Switch to a router Ethernet port
- Computer to switch
- Computer to hub
Detail:
2. Crossover UTP Cables
For two devices to communicate through a cable that is directly connected between the two, the transmit terminal of one device needs to be connected to the receive terminal of the other device.
The cable must be terminated so the transmit pin, Tx, taking the signal from device A at one end, is wired to the receive pin, Rx, on device B. Similarly, device B's Tx pin must be connected to device A's Rx pin. If the Tx pin on a device is numbered 1, and the Rx pin is numbered 2, the cable connects pin 1 at one end with pin 2 at the other end. These "crossed over" pin connections give this type of cable its name, crossover.
To achieve this type of connection with a UTP cable, one end must be terminated as EIA/TIA T568A pinout, and the other end terminated with T568B pinout.
To summarize, crossover cables directly connect the following devices on a LAN:
- Switch to switch
- Switch to hub
- Hub to hub
- Router to router Ethernet port connection
- Computer to computer
- Computer to a router Ethernet port
