Crossover cable
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A crossover cable connects two devices of the same type, for example DTE-DTE or DCE-DCE, usually connected asymmetrically (DTE-DCE), by a modified cable called a crosslink.[1] Such distinction of devices was introduced by IBM.
The crossing wires in a cable or in a connector adaptor allows:
- connecting two devices directly, output of one to input of the other,
- letting two terminal (DTE) devices communicate without an interconnecting hub knot, i.e. PCs,
- linking two or more hubs, switches or routers (DCE) together, possibly to work as one wider device.
Examples[edit]
-
A null modem cable.
- Null modem of RS-232
- Ethernet crossover cable
- Rollover cable
- A loopback is a type of degraded "one side crosslinked connection" connecting a port to itself, usually for test purposes.
Other technologies[edit]
Some connection standards use different balanced pairs to transmit data, so crossover cables for them have different configurations to swap the transmit and receive pairs:
- Twisted pair Token ring uses T568B pairs 1 and 3 (the same as T568A pairs 1 and 2), so a crossover cable to connect two Token Ring interfaces must swap these pairs, connecting pins 4, 5, 3, and 6 to 3, 6, 4, and 5 respectively.
- A T1 cable uses T568B pairs 1 and 2, so to connect two T1 CSU/DSU devices back-to-back requires a crossover cable that swaps these pairs. Specifically, pins 1, 2, 4, and 5 are connected to 4, 5, 1, and 2 respectively.
| Pin | Connection 1: T568A |
Connection 2: T568B |
Pins on plug face | ||
|---|---|---|---|---|---|
| pair | color | pair | color | ||
| 1 | 2 |  white/orange stripe |
1 |  blue solid |
 |
| 2 | 2 |  orange solid |
1 |  white/blue stripe |
|
| 3 | 3 |  white/green stripe |
3 | white/green stripe |
|
| 4 | 1 | blue solid |
2 | white/orange stripe |
|
| 5 | 1 | white/blue stripe |
2 | orange solid |
|
| 6 | 3 |  green solid |
3 | green solid |
|
| 7 | 4 |  white/brown stripe |
4 | white/brown stripe |
|
| 8 | 4 |  brown solid |
4 | brown solid |
|
- A 56K DDS cable uses T568B pairs 02 and 04, so a crossover cable for these devices swaps those pairs (pins 01, 02, 07, and 08 are connected to 07, 08, 01, and 02 respectively).
See also[edit]
References[edit]
- ^ Dean, Tamara (2010). Network+ Guide to Networks. Delmar. p. 657.
