There are RJ-11, RJ-12, and RJ-45 connectors. RJ-11 is typically used for telephone lines, while RJ-45 is used for NICs.
Bnc,rj-45
I am sure that phone jacks are RJ-11 not the larger RJ=45.
It means Connector type 11 of the RJ specification; RJ means Registered jacks - it is a telephone standard developed to standardize connectors in the telephone industry.
SC and RJ-45
RJ-11 is simply a standard conventional telephone jack, and RJ is short for "registered jack." If you find two RJ-11 connectors on the back of a computer, it means the computer has a dial-up modem. One of the connectors connects to a telephone wall jack. The other connector can be attached to a telephone. Most modems were made to where if the modem is in active use, any phone plugged into the modem would be disconnected so as to not interfere with the modem.
RJ-45 or 8P8C modular connectors
Coaxial Cable With RJ 45 Connectors at both the ends.
A fiber optic connection between server and router
10base-T uses for twister pair cable which speed 10mbps.
RJ stands for Registered Jack commonly used in Ethernet networking. The Ethernet cables has RJ45 connectors at both the ends.
According to the itt book ;) I came up with: Connectors for twisted pair cable include the modular RJ type of jacks and plugs (RJ-11;RJ-14; RJ-22; RJ-25; RJ-31; RJ-45; RJ-48; RJ-61) (of four, six, and eight position configurations) along with the hermaphroditic connector employed by IBM. The hermaphroditic connector is specific to STP and is also known as STP connector, IBM data connector, or universal data connector. The connector used with patch panels, punch-down blocks, and wall plates, is called an IDC (insulated displacement connector). If considered a connector, there is the modular Y-adapters used for splitting usually in 10Base-T, Token Ring, and voice applications. Also, if considered a connector, there is the crossover cable which is wired to a T586A pinout scheme on one end and a T586B pinout on the other end. Coax connectors used with video equipment are referred to as F-series connectors (primarily used in residential installations for RG-58, RG-59, and RG-6 coaxial cables). Coax cables used with data and video backbone applications use N-connectors (used with RG-8, RJ-11U, and thicknet cables). When coaxial cable distributes data in commercial environments, the BNC (Bayonet Niell-Concelman) connector is often used. It is used with RG-6, RG-58A/U thinnet, RG-59, and RG-62 coax cable. Fiber-optic connectors include SC, duplex SC, ST, duplex ST, FDDI, and FC. These relate to different types of fiber-optic cables and configurations. Three of the SFF connectors that have been propagated (during the life span of the book) for fiber-optic cables were LC, VF-45, and the MT-RJ.
Short for Registered Jack-45, an eight-wire connector used commonly to connect computers onto a local-area networks (LAN), especially Ethernets. RJ-45 connectors look similar to the ubiquitous RJ-11 connectors used for connecting telephone equipment, but they are somewhat wider.