Call yourself BERT testing of ISDN line

A portable ISDN test set contains test circuitry that is controllably operative to automatically test the ISDN communication capability of an ISDN circuit. In response to a user operating a prescribed input/output element of a user interface of the test set, the test set's supervisory control processor executes a routine that places an ISDN call over a first bearer channel of the ISDN circuit, the first bearer channel having a first directory number, through a public switched telephone network to a second directory number associated with a second bearer channel of the ISDN circuit. The ISDN call is thus routed by the public switched telephone network back to the ISDN test set. When the ISDN call is received by the test set, it is automatically looped to the public switched telephone network, so that the call is rerouted to the first directory number associated with the first bearer channel to the ISDN test set. When the looped back call is answered, a BERT is conducted over the dual looped bearer channel pair, thereby testing the full 128 Kbps bearer channel bandwidth of the ISDN circuit. The automated testing routine includes a subroutine that automatically derives the first and second directory numbers from respective user-supplied service profile identifiers for the first and second bearer channels.