Abstract: A test system (1) serves to check transmission processes in a mobile radio network (2). The latter comprises a central switching computer (8), a local mobile telephone (13) equipped for SIM communication, and a transmission unit (3) comprising a local transmission unit (5). Other components of the test system (1) include a local SIM simulation computer (10), which is connected to the local transmission unit (5) on one hand and to the mobile telephone (13) on the other hand, a control computer (23), which is used for controlling the testing operation, and which is connected to the mobile radio network (2), as well as an authentication computer (14), which is connected to the SIM simulation computer (10) and with which the mobile telephone (13) can be authenticated. For the authentication, a method is used that requires only two communication steps over the remote signal connection.