Transmission line simulation for testing ISDN devices

A transmission line model has been developed to simulate the effects of sourcing ISDN (integrated services digital network) waveforms through twisted-pair telephone cable. Circuit simulation models for three different wire gauges have been used to predict the transmission characteristics of arbitrary networks using SPICE simulations. These models have been configured to simulate a standard test network specified by ANSI and have demonstrated good correlation with an actual twisted-pair telephone test network. The models correctly simulate the input and output impedances imposed by cable and effectively model the transmission effects of mismatched terminations. From the simulated frequency response, FIR (finite impulse response) filter coefficients can be derived to allow DSP (digital signal processing) of test waveforms. This allows the testing of ISDN transceivers using signals likely to be encountered in their intended application