RJ-48
(Registered Jack-48) A telephone connector that holds up to eight wires. It uses the same plug and socket as RJ-45 but has different pinouts. RJ-48C is commonly used for T1 lines and uses pins 1, 2, 4 and 5. RJ-48X is a variation of RJ-48C that contains shorting blocks in the jack so that a loopback is created for troubleshooting when unplugged. RJ-48S uses pins 1, 2, 7 and 8 and is commonly used for 56 Kbps digital lines (DDS).
RJ-45
(Registered Jack-45) A telephone connector that holds up to eight wires. RJ-45 plugs and sockets are used in Ethernet and Token Ring Type 3 devices. Eight-wire RJ-45 connectors are used with Ethernet and Type 3 Token Ring networks.
