Telephonic communications – Plural exchange network or interconnection – Interexchange signalling
Reexamination Certificate
2000-08-01
2001-10-09
Matar, Ahmad (Department: 2642)
Telephonic communications
Plural exchange network or interconnection
Interexchange signalling
C379S198000, C379S239000
Reexamination Certificate
active
06301353
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the field of communications, and in particular to the operation of a PABX.
BACKGROUND TO THE INVENTION
In the operation of a PABX, a subscriber dials a sequence of digits which are used by the PABX to complete a call to a line or trunk identified by at least some of the dialed digits. In the event the subscriber dials a prefix such as a 9, the PABX connects the calling subscriber line to an outgoing trunk, whereupon subsequently dialed digits following the 9 are passed to a central office to which the outgoing trunk is connected, for completion of the call.
The call numbering plan used in e.g. North America has used a convention which avoids confusion between area code numbers and central office numbers. Central office numbers have been restricted to the middle digit of the first three digits being between 2 and 9 inclusive, and the middle digit of area codes have been restricted to 0 or 1.
These restrictions have been removed. Area codes and office codes are now interchangeable.
In addition, in the past each telephone company had a monopoly in local service, and the dialed numbers automatically were detected by central office equipment owned by that telephone company. Long distance service was either provided by the local company (in some jurisdictions), or the long distance carrier was selected by the local telephone company. This monopoly has been broken, and the local subscriber can select the long distance company to use.
This creates a difficulty for PABXs, since they must be able to distinguish between digits dialed within a PABX, digits dialed which are to a called subscriber accessable via a local central office, and digits dialed which are to be connected via an alternate service provider, without being able to distinguish between area codes and other numbers based on the value of the second digit of the called number that is dialed, as in the past. Yet it is important to do so automatically, in order to take advantage of savings which can be obtained by use of alternate service providers.
For example, in order to route to central office 416 in the local area, a PABX owner would have to program an automatic route selection subsystem in the PABX to interpret the number
9416
+4 digits to follow (the number 9 designating an out-of-PABX call) as meaning that the call should be routed to the local central office, and to interpret the number
9416
+7 digits to follow as meaning that the call should be routed to an alternate service provider. It is generally not possible to do this on common PABXs, since the prefix 9 automatically causes the call to be routed to the local central office.
SUMMARY OF THE INVENTION
The present invention provides means and method for a PABX owner to allow subscribers to access trunks and lines defined by the area codes and central office codes which do not conform to the previous standard, and at the same time to access the alternate service providers, via the PABX.
In accordance with an embodiment of the present invention, the PABX can be programmed with the same leading and dialed digits, but with different digits to follow (dtf), and yet will follow different call completion communication routes. The different routes are determined by the different numbers of digits to follow. In this manner the PABX owner can program various call completion routes for varying lengths of total number of digits dialed by the subscriber without having to explicitly define all digit combinations of the automatic route selection subsystem.
In accordance with an embodiment of the present invention, in a PABX switching system, a method and apparatus for establishing a communication route from dialed digits is comprised of (a) receiving dialed digits relating to a call, (b) storing a table of groups 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 communication route, each list of quantities of digits being sorted in ascending order, (c) detecting the values of the received dialed digits, determining whether an initial group of digits has been dialed which corresponds to a group of initial digits stored in the table, counting a number of digits following the initial group of dialed digits and generating a digits-to-follow (dtf) signal, and selecting the communication route by an index corresponding to the value of the dtf signal within the subtable corresponding to the values of the initial digits, and (d) using the communication route for completion of the call.
In accordance with another embodiment, in a PABX switching system, a method and apparatus for establishing a communication route from dialed digits is comprised of (a) receiving dialed digits relating to a call, (b) storing a table of groups 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 communication route, each list of quantities of digits being sorted in ascending order, (c) selecting a group of initial digits in the table corresponding to first digits of the dialed digits, and pointing to a communication route corresponding to a lowest quantity of digits in a subtable of selective group of initial digits, (d) using the 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) detecting a dialed digit in excess of the quantity of digits and pointing instead to a next highest quantity of digits in the subtable of the selected group of initial digits, and (f) repeating step (e) until no dialed digit is detected which is in excess of a highest quantity of digits pointed to and using a corresponding communication route listed in the subtable for completion of the call.
REFERENCES:
patent: 4571463 (1986-02-01), Shefler
patent: 4661974 (1987-04-01), Bales et al.
patent: 5272749 (1993-12-01), Masek
patent: 5325422 (1994-06-01), Ladd
patent: 5479494 (1995-12-01), Clitherow
Lyon Steven G.
Maclsaac Brian
Baker Harold C.
Bui Bing
Hendry Robert G.
Matar Ahmad
Mitel Corporation
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