Limits of the ISDN S-interface

The limits of the ISDN S-interface are determined for the short passive bus, extended bus and point-to-point wiring configurations by means of a computer simulation. The simulation can be used as a tool in projecting an in-house installation. The model for simulating the S-bus is based on the well-known theory of transmission line. With an interactive program an ultimate bus configuration can be found which still meets the requirements of the CCITT specifications I.430 and of the received minimum eye opening at the network termination (NT). The latter is related to a bit error rate objective of the interface. The length of the bus, the length of the cords, the number of terminals and their places on the bus are input variables to the program. The transmitter output impedance, the receiver input impedance and the cable parameters are taken into account as frequency-dependent variables in the program