| 摘要 |
In a PABX switching system: (a) apparatus for receiving dialed digits relating to a call, (b) apparatus for storing a table of groups of predetermined numbers of initial digits and for each group of initial digits storing a subtable, each subtable being comprised of a list of quantities of digits expected to follow a corresponding group of initial digits, each quantity being correlated with a central office or an alternate communication route, each list of quantities of digits being sorted in ascending order, (c) apparatus for selecting a group of initial digits in the table corresponding to first digits of the received dialed digits, and for pointing to a central office or alternate communication route corresponding to a lowest quantity of digits in a subtable of the selected group of initial digits, (d) apparatus for using the central office or alternate communication route for completion of the call in the event the dialed digits contain a quantity of digits corresponding to the lowest quantity of digits, (e) apparatus for detecting a dialed digit in excess of the lowest quantity of digits and for pointing instead to a next higher quantity of digits in the subtable of the selected group of initial digits, and (f) apparatus for repeating step (e) until no dialed digit is detected which is in excess of a highest quantity of digits pointed to and apparatus for using the corresponding communication route listed in the subtable for completion of the call.
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