What are the RJ Standards?

RJ
The prefix ‘RJ’ refers to 'Registered Jack'. Recognized by the Code of Federal Regulations and used to provide access to a public switched telephone network (PSTN).  In the U.S., these are voice and data, plug and wire configurations (receptacle and plug) connection interfaces registered with the FCC. A registered jack has a specific number associated with the wiring scheme and function it is used for, such as RJ-45. The term ‘RJ’ was first introduced by the Regional Bell Operating Companies (RBOC’s) to indicate to a field technician what was going to be attached to the jack and how to wire it up.  In the telecommunications industry this has become an acceptable means of referring to a type of jack connector.  However, a precise way to identify a jack would be to examine how many positions (width) and how many conductors are used.

RJ-11
This modular jack configuration is possibly the most used jack in the world. It is a 4-wire scheme terminated with a six conductor jack used to connect asynchronous devices such as telephones, modems, and fax machines to a female RJ-11 outlet on the wall.  The female outlet is then connected to the telephone network line via twisted pair wire.

RJ-45
This modular jack is configured with 8 positions typical in data networks and data communication devices, e.g., punch down panels, switches, hubs, routers and broadband modems.

Examples:
The modem found in your computer communicates using flat wire cable with a RJ-11 jack.  Similarly the network interface card (NIC) in your PC uses twisted pair cable with a RJ-45 jack for data communications. You can use normal telephone wire or a cable with a specific category rating.

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Registered Jack	Width (Positions)	Pins Installed	Installed Pins		Uses
RJ-10	4 Position	4 Installed	1,2,3,4		Voice & data
RJ-11	6 Position	4 Installed	2,3,4,5		standard telephone connection, data
RJ-12	6 Position	6 Installed	1,2,3,4,5,6		telephone, data
RJ-14	6 Position	4 Installed	2,3,4,5		connection for 2 analog phone lines
RJ-45	8 Position	8 Installed	1,2,3,4,5,6,7,8		ISDN, LAN, data
RJ-48	10 Position	8, 10 Installed	1,2,3,4,5,6,7,8, 9,10		WAN