Jump to content

8P8C

From Wikipedia, the free encyclopedia
This is an old revision of this page, as edited by T3h (talk | contribs) at 09:14, 11 August 2007 (→Wiring: Crossover cables are red, not orange). The present address (URL) is a permanent link to this revision, which may differ significantly from the current revision.
An 8P8C modular plug that has yet to be crimped onto a cable
Connector and cable

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 the US 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 for U.S. telephone applications by the Administrative Council for Terminal Attachment (ACTA) in national standard ANSI/TIA-968-A. 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.

For data communication applications (LAN, structured cabling), International Standard IEC 60603 specifies in parts 7-1, 7-2, 7-4, 7-5, and 7-7 not only the same physical dimensions, but also high-frequency performance requirements for shielded and unshielded versions of this connector for frequencies up to 100, 250 and 600 MHz, respectively.

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 a red 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. 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.

Other applications include other networking services such as ISDN and T1.

The 8P8C modular connector is also used for RS-232 serial interfaces according to the EIA/TIA-561 standard[1].

See Registered jack for other, similar looking jacks, with which the 8P8C modular connector is likely (and often) confused, mainly because it is often falsely called "RJ45".

In floodwired [1] environments the center (blue) pair is often used to carry telephony signals. Where so wired, the physical layout of the 8P8C modular jack allows for the insertion of an RJ11 plug in the center of the socket, provided the RJ11 plug is wired in true compliance with the U.S. telephony standards (RJ11) using the center pair. The formal approach to connect telephony equipment is the insertion of a type-approved converter.

The remaining (brown) pair is increasingly used for Power over Ethernet (POE). Legacy equipment may conflict with this use as manufacturers used to short circuit unused pairs to reduce signal crosstalk. Some routers/bridges/switches can be powered by the unused 4 lines — blues(+) and browns(-) — to carry current to the unit.

Beware: Different manufacturers of 8P8C modular jacks arrange for the pins of the 8P8C modular connector socket to be linked to wire connectors (often IDC type terminals) that are in a different physical arrangement from that of other manufacturers: Thus, for example, if you are in the habit of connecting your white/orange wire to the "bottom right hand" IDC terminal, which links it to 8P8C modular connector pin 1, be aware that on jacks made by other manufacturers this terminal may instead connect to 8P8C modular connector pin 2 (or any other pin, for that matter).

"RJ45" naming confusion

As mentioned above, the term "RJ45" may refer to two rather different things. To avoid ambiguity in this section, they will be referred to as true telephone RJ45 and computer "RJ45". Except where otherwise indicated, this article is about the computer "RJ45" alone.

Originally, there was only the true telephone RJ45. It is one of the many registered jacks, like RJ11, a standard from which it gets the "RJ" in its name. As a registered jack, true telephone RJ45 specifies a physical connector, and also the wiring of it. The true telephone RJ45 uses a special, keyed 8P2C modular connector, with Pins 5 and 4 wired for tip and ring of a single telephone line and Pins 7 and 8 connected to a programming resistor. It is meant to be used with a high speed modem, and is obsolete today.

Telephone installers who installed true telephone RJ45 jacks in the past were familiar with the inner workings which made it RJ45, but their clients saw only a hole in the wall of a particular shape, and came to understand RJ45 as the name for a hole of that shape. When they found similar-looking connectors being used in entirely non-telephone applications, usually connecting computers, they called these "RJ45", too. This was therefore the so-called computer "RJ45".

Compounding the problem was the fact that the physical connectors indicated by true telephone RJ45 are not even compatible with computer "RJ45" connectors. True telephone RJ45 connectors are a special variant of 8P2C, meaning only the middle 2 positions have conductors in them, while pins 7 and 8 are shorting a programming resistor. Computer "RJ45" is 8P8C -- all eight conductors are always present. Furthermore, true telephone RJ45 involves a "keyed" variety of the 8P body, which means it may have an extra tab that a computer "RJ45" connector is unable to mate with.

Because true telephone RJ45 never saw wide usage and computer "RJ45" has become well known today, computer "RJ45" is almost always what a person is referring to when they say "RJ45". Electronics catalogs not specialized to the telephone industry advertise 8P8C modular connectors as "RJ45". Virtually all electronic equipment that uses an 8P8C connector (or possibly any 8P connector at all) will document it as an "RJ45" connector.

There have been conflicts when clients demand "RJ45" and an installer insists that they ask for something else or they will get something quite different from what they actually need.

Rounding out the confusion in "RJ45" naming is the fact that some people intend for the term to encompass not just the connector shape and size, but the wiring standard for it described by TIA/EIA-568-B as well. So one might find "Here is the pinout of an RJ45 jack."

See also

Notes

  1. ^   floodwire is a chiefly British term for installing communications cables in a massive fashion in anticipation of their eventual use.

References

  • ANSI/TIA-968-A: Telephone terminal equipment – Technical requirements for connection of terminal equipment to the telephone network
  • IEC 60603-7-1: Connectors for electronic equipment - Part 7-1: Detail specification for 8-way, shielded free and fixed connectors with common mating features, with assessed quality
  • IEC 60603-7-2: Connectors for electronic equipment - Part 7-2: Detail specification for 8-way, unshielded, free and fixed connectors, for data transmissions with frequencies up to 100 MHz
  • IEC 60603-7-4: Connectors for electronic equipment - Part 7-4: Detail specification for 8-way, unshielded, free and fixed connectors, for data transmissions with frequencies up to 250 MHz
  • IEC 60603-7-5: Connectors for electronic equipment - Part 7-5: Detail specification for 8-way, shielded, free and fixed connectors, for data transmissions with frequencies up to 250 MHz
  • IEC 60603-7-7: Connectors for electronic equipment - Part 7-7: Detail specification for 8-way, shielded, free and fixed connectors, for data transmissions with frequencies up to 600 MHz
Retrieved from "https://en.wikipedia.org/w/index.php?title=8P8C&oldid=150564951"