RJ45 / Cat5

8P8C is short for "eight positions, eight conductors", and so an 8P8C modular connector (plug or jack) is a modular connector with eight positions, all containing conductors. more...

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The 8P8C modular plugs and jacks look very similar to the plugs and jacks used for FCC's registered jack RJ45 variants, although the true RJ45 is not really compatible with 8P8C modular connectors. It neither uses all eight conductors (but only two of them for wires plus two for shorting a programming resistor) nor does it fit into 8P8C because the true RJ45 is "keyed".

Despite this, outside of the U.S. telecommunications industry, 8P8C modular connectors are nearly always called "RJ45" — which leads to a lot of confusion when telecommunication professionals meet with network installers. See below for a discussion of telecom's/FCC's true RJ45 and the confusion that is created by the use of the term "RJ45" for 8P8C modular connectors popularly used in computer networking.

An 8P8C modular connector has two forms: the male plug and the female jack or socket. Each has eight conductors.

The 8P8C modular connector is probably most famous for its use in Ethernet. Since about 2000, it is nearly universal as the type of connector used on a cable that carries a single Ethernet network. But it is also popular for a variety of other things.

The 8P8C modular connector has replaced many older connector types because of its smaller size and relative ease of plugging and unplugging. Older connectors have also been phased out as modern electronic equipment no longer has the high current and voltage requirements for which the bulkier connectors were designed. Current technology is able to do more with a single wire than equipment of the past, and the eight conductors of an 8P8C modular connector have been sufficient for most modern applications.

The shape and dimensions of an 8P8C modular connector are specified by the standard TIA-968-A, published by the Administrative Council for Terminal Attachment (ACTA). This standard does not use the short term 8P8C and covers more than just 8P8C modular connectors, but the 8P8C modular connector type is the eight position connector type described therein, with eight conductors installed.

Wiring

It is frequently terminated using the T568A or T568B pin/pair assignments that are defined in TIA/EIA-568-B.

A cable that is wired as T568A at one end and T568B at the other is a "crossover" cable. Such a cable often has an orange sheath and, before the widespread acceptance of auto-MDI/MDIX capabilities, was needed to connect a switch to a switch or router to a router.

Ethernet is most commonly carried over Category 5e cable or Category 6 cable with an 8P8C modular plug crimped on each end.

Applications

A very common application is in Ethernet cables, where the plug on each end is an 8P8C modular plug wired according to TIA/EIA-568-B (but with only 4 of the wires actually used). Such a cable might connect a computer to a network wall jack or connect a cable or DSL modem to a computer Ethernet network card.

Read more at Wikipedia.org