The telephony service non-accessibility denotes the probability that the end-user cannot access the mobile telephony service when requested if it is offered by display of the network indicator on the UE.

NOTE: Due to network problems and despite B-party being not busy (see preconditions for measurement), it may even be possible for the A-party to receive a busy or not reachable signal. In this case, since no ALERTING message will be sent, the test sample will be treated as a failure.