A max. of 16 restriction tables (LDSRT) can be administrated with the AMO LDSRT. Each of these tables allows the blocking of individual digit strings, which can be broken down into two areas (FDS and SDS). The digit pattern fields to be included for the check of the FDS/SDS areas­ are specified in AMO LDPLN. The applicable table is optionally assigned one or more routes when using the restriction tables in AMO LDAT with the parameter LDSRT.

If no correlation between the administrated areas (FDS and SDS) is found with the specified digit pattern fields in the digit pattern dialed, the LCR for this route is continued.

If the entries in the LDSRT table agree with the specified digit pattern fields, the connection is not established via this route (trunk group) and the LCR is continued with the next route. (If no further route is defined, or if the authorization is inadequate, the LCR is terminated.)

This feature is typically used if a system is connected to several carriers. Certain digit sequences (digit strings) are not, however, accepted by all carriers.