Abstract: A test unit for data communication networks is formed by placing one or more application modules between a front module and a rear module. The modules are secured together with a latching system and a bus structure provides for control and performance information transfers between modules. The front module may serve a user interface via a touch screen. In addition, the front module has a variety communication ports that provide for one or more remote user interfaces. Battery packs are located in the front module and the rear module for providing power to the test unit.