The DLS 400 simulates various local loops for testing Asymmetrical Digital Subscriber Loop (ADSL) transmission products and other high speed digital subscriber loop technologies. It reproduces the exact characteristics of real telephony cable using networks of passive discrete components (L,R,C), thus reproducing both the A.C. and D.C. characteristics of the line. The DLS 400 contains hundreds of segments of cable simulation which can be matrixed together in various configurations and line lengths. In analog terms, the DLS 400 reproduces cable accurately up to 1.5 MHz and in some configurations up to 2.0 MHz. In all, 28 preset test loops for testing ADSL are provided and several others can be created by the user. The DLS 400 comes complete with an IEEE-488 (GPIB) interface which conforms to SCPI specifications for integration into computer controlled test systems.