>Hi group members
>
>In TP cables we have eight wires. Only four are used. Why we need
>the other four. The same thing applies to DB-25 and other types of
>cables. We don't use all of the wires. Why?
>
>Regards to all
>
For the RJ45 connector used with ISDN, the intention of the standards
bodies was to have additional wires available for powering either the
TE or NT. There are some power configurations that do not rely on
the phantom DC imposed on the signal-carrying wires.
The X.21 serial connector needs two pairs each for data and clock in
each direction. This was originally on a DB-15, but RJ45 is common.
Of course, RS-232 on a DB-25 historically involved many more wires
when in half-duplex and/or synchronous applications, and still may in
dial applications.
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