RJ-48 plug

An RJ-48 plug is often mistaken for RJ-45. On the outside, the two look identical—both are housed in miniature 8-position jacks. The difference is in the wire pairing. RJ-48 connectorIn RJ-48, two of the wires are for transmit, two are for receive, and two are for the drain. The last two wires are reserved for future use.

Three subsets

There are three subsets within RJ-48: RJ-48C, RJ-48X, and RJ-48S. RJ-48C and RJ-48X are very similar, though RJ-48C is more common. Both use lines 1, 2, 4, and 5, and connect T1 lines. RJ-48X connectors, however, have shorting bars. RJ-48S uses lines 1, 2, 7, and 8, and generally connects 56K DDS lines.

Here’s how RJ-48C pinning compares to RJ-48S pinning:

RJ-48C and RJ-48S pinning
Pin RJ-48C RJ-48S
1 Receive ring Receive data +
2 Receive tip Receive data -
3 No connection No connection
4 Transmit ring No connection
5 Transmit tip No connection
6 No connection No connection
7 No connection Transmit data +
8 No connection Transmit data -
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