Connecting the telephone system
22
Connecting several ISDN telephones by using an S
0
bus
As an alternative to directly connecting the telephones you can also install an S
0
bus
from the telephone system. In order to do so below the telephone system you must
install an ISDN wall socket or a universal wall socket. With ISDN wall socket outlets
both jacks are in parallel, with universal wall socket outlets the two jacks can be con-
nected to separate cables. In case you installed a universal wall socket outlet below
the telephone system you can install two S
0
buses at this outlet.
At pins 1a, 1b, 2a, and 2b (with a universal wall socket at pins 3, 4, 5, and 6) a tele-
phone or network cable has to be connected. At the other end of the cable another
ISDN- or universal wall socket and starting form this where applicable further ISDN-
or universal wall sockets can be connected. Wiring has to be made 1:1 (no cross-
over).
The last ISDN wall socket will have to carry a (100 Ohms) termination resistor be-
tween 1a and 1b and between 2a and 2b each. With a universal wall socket termina-
tion are between pins 4 and 5 and between Pins 3 and 6.
Termination resistors are also available for plugging them into the jack of the last out-
let, and also ISDN wall sockets with integrated (switched) termination resistors are
available.