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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
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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
Cable may refer to:
Mechanical
* Nautical cable, an assembly of three or more ropes woven against the weave of the ropes, rendering it virtually waterproof
* Wire rope, a type of rope that consists of several strands of metal wire laid into a hel ...
called a crosslink. Such a distinction between devices was introduced by IBM.
The crossing of 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
In electrical engineering, a switch is an electrical component that can disconnect or connect the conducting path in an electrical circuit, interrupting the electric current or diverting it from one conductor to another. The most common type of ...
or routers (DCE) together, possibly to work as one wider device.
In contrast, a straight-through cable uses direct wiring to connect complementary devices, e.g. a PC to a switch.
Concept
Straight-through cables are used for most applications, but crossover cables are required in others. In a straight-through cable, pins on one end correspond exactly to the corresponding pins on the other end (pin 1 to pin 1, pin 2 to pin 2, etc.). Using the same wiring scheme at each end yields a straight-through cable (a given color wire connects to a given number pin, the same at both ends). In this case, the terminations are identical, so only one pinout is required. In a crossover cable, pins do not correspondsome or all of the conductors are swapped at the terminations. For example, if pin 1 on one end goes to pin 2 on the other end, then pin 2 on one end goes to pin 1 on the other end, and the other pins remain unaffected. Such crossover cables are electrically symmetrical, meaning that they work identically regardless of which way you plug them in (if you turn the cable around, it still connects the same pins as before). Using different wiring at each end yields a crossover cable (a given color wire connects to one number pin at one end, and a different number pin at the other).Examples
* Null modem
Null modem is a communication method to directly connect two DTEs (computer, terminal, printer, etc.) using an RS-232 serial cable. The name stems from the historical use of RS-232 cables to connect two teleprinter devices or two modems in orde ...
of RS-232
In telecommunications, RS-232 or Recommended Standard 232 is a standard originally introduced in 1960 for serial communication transmission of data. It formally defines signals connecting between a ''DTE'' (''data terminal equipment'') such a ...
* Ethernet crossover cable
An Ethernet crossover cable is a crossover cable for Ethernet used to connect computing devices together directly. It is most often used to connect two devices of the same type, e.g. two computers (via their network interface controllers) or two ...
* Rollover cable
Rollover cable (also known as a Yost cable, Cisco cable, or a Console cable) is a type of null-modem cable that is used to connect a computer terminal to a router's console port. This cable is typically flat (and has a light blue color) to help ...
* A loopback
Loopback (also written loop-back) is the routing of electronic signals or digital data streams back to their source without intentional processing or modification. It is primarily a means of testing the communications infrastructure.
There are m ...
is a type of degraded "one side crosslinked connection" connecting a port to itself, usually for test purposes.
Other technologies
Some connection standards use differentbalanced pair
In telecommunications and professional audio, a balanced line or balanced signal pair is a circuit consisting of two conductors of the same type, both of which have equal impedances along their lengths and equal impedances to ground and to other ci ...
s to transmit data, so crossover cables for them have different configurations to swap the transmit and receive pairs:
* Twisted pair Token Ring
Token Ring network
IBM hermaphroditic connector with locking clip. Screen contacts are prominently visible, gold-plated signal contacts less so.
Token Ring is a computer networking technology used to build local area networks. It was introduc ...
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.
* A 56K DDS cable uses T568B pairs 2 and 4, so a crossover cable for these devices swaps those pairs (pins 1, 2, 7, and 8 are connected to 7, 8, 1, and 2 respectively).
See also
* Electrical connector wiring *Pinout
In electronics, a pinout (sometimes written "pin-out") is a cross-reference between the contacts, or ''pins'', of an electrical connector or electronic component, and their functions. "Pinout" now supersedes the term "basing diagram" that was the s ...
* Structured cabling
* ANSI/TIA-568
ANSI/TIA-568 is a technical standard for commercial building cabling for telecommunications products and services. The title of the standard is ''Commercial Building Telecommunications Cabling Standard'' and is published by the Telecommunication ...
References
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