Date created: 02/13/20 07:49:41. Last modified: 02/13/20 07:52:59

Copper Connectors


8P8C == A typically unkeyed connector or plug.

RJ45 == A typically unkeyed 8P8C connector which mates with an 8P8C plug and wired using the TIA/EIA-568-A/B standard common in Ethernet applications.

RJ45S == A typically keyed 8P8C connector which mates with an 8P2C plug using a different wiring standard common in analogue telephone systems.

RJ48 == A typically unkeyed 8P8C connector which fastens to shielded twisted pair (STP) cables and used for T1 and ISDN services.

RJ48S == A typically keyed 8P8C connector, variation on RJ45, also used for analogue TDM telephony.

RJ61 == A typically unkeyed 8P8C connector used for four terminating analogue telephone lines.

8P8C Variations
the 8P8C modular connector type is often inaccurately labeled RJ45 because the registered jack standard of that name specified 8P8C modular connectors. A common use of 8P8C connectors is Ethernet over twisted pair. Likewise, the 4P4C connector is sometimes erroneously called RJ9 or RJ22—no such official designations exist—and various six-position modular connectors may be incorrectly called RJ11.
(or 8PMJ, 8-position modular jack)

Although commonly referred to as RJ45 in the context of Ethernet and category 5 cables, this is incorrect in the context of a generic 8P8C connector. A telephone-system-standard RJ45 plug has a key which excludes insertion in an un-keyed 8P8C socket. The FCC Registered Jack (RJ) program specified a different mechanical interface and wiring scheme than TIA/EIA-568-B for RJ45S. TIA/EIA-568-B is often used for modular connectors used in Ethernet and telephone applications. Generic 8P8C modular connectors are similar to those used for the FCC RJ45 variants, although the RJ45S jack is not compatible with 8P8C modular connectors.

The original RJ45S jack mates with a keyed 8P2C modular plug, and has pins 4 and 5 (the middle positions) wired for the ring and tip conductors of a single telephone line and pins 7 and 8 shorting a programming resistor. It was intended for high speed modems, and is obsolete.

Telephone installers who wired RJ45S modem jacks or RJ61X telephone jacks were familiar with the pin assignments of the standard. However, the standard un-keyed modular connectors became ubiquitous for computer networking, and informally inherited the name RJ45. RJ45S uses a keyed variety of the 8P body, meaning it has an extra tab that a common modular connector cannot mate with.

Because telephone RJ61 and data RJ45/RJ48 connectors were not widely used and 8P8C connectors in computers became ubiquitous, RJ45 is used to refer to 8P8C un-keyed modular connectors. This practice is followed by electronics catalogs and many electronic equipment manuals. In common usage, RJ45 may also refer to the pin assignments for the attached cable, which are actually defined as T568A and T568B in wiring standards such as TIA/EIA-568.
A similar standard jack once used for modem/data connections, the RJ45S, used a "keyed" variety of the 8P8C body with an extra tab that prevents it mating with other connectors; the visual difference compared to the more common 8P8C is subtle, but it is a different connector. The original RJ45S keyed 8P2C modular connector had pins 5 and 4 wired for tip and ring of a single telephone line and pins 7 and 8 shorting a programming resistor, but is obsolete today.
RJ48 is a registered jack. It is used for T1 and ISDN termination and local area data channels/subrate digital services. It uses the eight-position modular connector (8P8C).

RJ48C is commonly used for T1 circuits and uses pin numbers 1, 2, 4 and 5.
RJ48S is typically used for local area data channels and subrate digital services, and carries one or two lines. It uses a keyed variety of the 8P8C modular connector.

RJ48 connectors are fastened to shielded twisted pair (STP) cables, not the standard unshielded twisted pair (UTP) CAT-(1–5).
RJ61 is a physical interface often used for terminating twisted pair type cables. It uses an eight position, eight conductor (8P8C) modular connector.

This pinout is for multi-line telephone use only; RJ61 is unsuitable for use with high-speed data, because the pins for pairs 3 and 4 are too widely spaced for high signaling frequencies. T1 lines use another wiring for the same connector, designated RJ48. Ethernet over twisted pair (10BASE-T, 100BASE-TX and 1000BASE-T) also use a different wiring for the same connector, either T568A or T568B. RJ48, T568A, and T568B are all designed to keep pins close together for pairs 3 and 4.

The flat eight-conductor silver-satin cable traditionally used with four-line analog telephones and RJ61 jacks is also unsuitable for use with high-speed data. Twisted pair cabling is required for data applications. Twisted-pair data patch cable used with the three data standards is not a direct replacement for RJ61 cable, because RJ61 pairs 3 and 4 would be split among different patch cable twisted pairs, causing cross-talk between voice lines 3 and 4 that might be noticeable for long patch cables.

With the advent of structured wiring systems and TIA/EIA-568-B conventions, the RJ61 pinout is falling into disuse. The T568A and T568B standards are used in place of RJ61 so that a single wiring standard in a facility can be used for both voice and data.
ANSI/TIA/EIA-568-A cabling covers the original Category 5 (100Mhz) cable, Category 5e (100 MHz), 6 (250 MHz), 6A (500 MHz), 7 (600MHz), and 8 (2,000 MHz).

6P6C Variations
The 6P2C, 6P4C, and 6P6C modular connectors are probably best known for their use as RJ11, RJ14, and RJ25 registered jacks, respectively. These interfaces use the same six-position modular connector body, but have different numbers of pins installed.

RJ11 is a physical interface often used for terminating single telephone lines. RJ14 is similar, but for two lines, and RJ25 is for three lines. RJ61 is a similar registered jack for four lines, but uses an 8P8C connector.


Previous page: BGP-ORR
Next page: Ethernet OAM and CFM Standards