Abstract: A device for testing a data carrying service operating over a telecommunications line. The device comprises a plurality of test circuits, each test circuit arranged to determine and test one or more characteristics of a data carrying service and providing means to emulate a termination of said telecommunication line, processing means operable to control the operation of each of said plurality of test circuits, and connection means arranged to connect said telecommunication line to one or more of said plurality of test circuits. The said data carrying service remains connected to said connection means during all of the testing operations provided by said one or more of the test circuits. This enables the device to automatically determine the identity of the data carrying service.