GB2303995A - Switching method and system with portable directory numbers - Google Patents

Description

1 SWITCHING METHOD AND SYSTEM WITH PORTABLE DIRECTORY NUMBERS 2303995 This

invention relates to a switching system and method for providing single portable directory numbers to users of a communications system.

Corporations and large institutions often use several PABXs to which lines of telephone sets or other station apparatus of employees are connected. Employees (referred to as subscrIbers, below) are sometimes moved from one department to the other, and in many such cases their telephones must be terminated on different PABXs than before the move. It is advantageous for these employees to retain their previous telephone numbers in order that telephone directories need not have to be reprinted or reprogrammed, and so that speed or other automatic dialers do not need to be reprogrammed. The service of retention of the same telephone number after a subscriber has moved to a line connected to another PABX is called portable directory numbers.

Previously, it was required that a system administrator program a specific route in a route selection table for each directory number which is to be moved from a local PABX, to provide portable directory numbers in a cluster of PABXs. This, however, has proved to be extremely complex to maintain for any significant time duration, or where there is a high volume of directory number locations to be changed. In addition most PABX systems place a limit on the number of routes that can be programmed, and some PABXs are very limited in the way in which dialing conflicts are handled between similar numbers used on more than one PABX.

2 In an embodiment to be described below, as an example illustrative of the present invention, a group of PABXs, defined herein as a cluster of PABXs, which offers portable directory numbers has a common directory number pool stored in a central database, i.e. no two directory numbers among the pool of directory numbers for all of the PABXs in the cluster are the same. This substantially eliminates the problem of dialing conflicts.

In one particular arrangement to be described below and illustrative of the invention, a method of processing a call within a cluster of PABXIS includes the steps of receiving a dialed directory number designating a called line within the cluster, accessing a database and obtaining an identity of a terminating PABX within the cluster on which a line corresponding to the dailed directory number is terminated, seizing a trunk, and generating and transmitting a message to the terminating PABX which identifies the terminating PABX and the dialed directory number, at the terminating PABX recognizing the terminating PABX identification and as a result translating the dialed directory number to an electrical line location, and completing the call on the terminating PABX to the line corresponding to the dialed directory number.

In another arrangement to be described below and illustrative of the invention, a method of processing a call within a cluster of PAMIS includes the steps of storing in a database: (a) a first table which corresponds telephone numbers with indexes to a second table defining the identities of PAM9 within the cluster on which called directory numbers are to be terminated, (ii) the second table corresponding the indexes with identities of the PABXs, (M) a third table which corresponds the indexes with directory numbers of lines terminating on the PABXs, (b) receiving 3 in an originating PABX in the cluster a set of dialed digits corresponding to a telephone number of a called party, (c) accessing the first table using the set of dialed digits to obtain an index, (d) accessing the second and third tables using the index to obtain an identity number of a terminating PABX on which a called party line is terminated and a directory number of the called party line on the terminating PABX, (e) assembling the identity number and the directory number 10 in a message format and sending the message to the PABX to complete a call to the called party in a manner as if the message containing the identity number and the directory number had been dialed from an originating line.

is A better understanding of the Invention will be obtained by reading the following description with reference to the following drawings, in which:

Figure 1 is a block diagram of a cluster of PAMs, Figure 2 is a block diagram of an originating PABX showing a call process during the origination of a call, Figure 3 Is a block diagram of a terminating PABX showing a call process during the completion of a call, Figure 4 is a block diagram of database in accordance with a preferred embodiment of the invention, Figure 4A is a table form for a corporate directory table, Figure 4B is a table form for a remote destination number table, 4 Figure 4C is a table form for assignment of cluster element (e.g. station apparatus) directory numbers to their host PAM, and Figure 5 is a diagram used to illustrate an example of operation of the invention.

Figure 1 illustrates a cluster of PABXs 1A, 1B and 1C, which may be model SX-2000 sold by Mitel Corporation. The structure of this PABX is described in U.S. Patents 4,615,028 issued September 30, 1986 and 4,616,360 issued October 7, 1986, invented by Conrad Lewis, which patents are incorporated by reference. Each PABX of the cluster is given a cluster number, which is shown on each PABX of the Figure as 159. Each PABX has its own cluster element identity (number) CEID, shown on the various PABXs as 5200, 5201, 5202, etc. Various lines connected to the PABXs have directory numbers, such as extension 4000 associated with PABX 1A, and extension 4001 associated with PABX 1C.

The cluster of PABXs are connected together via trunks or other signaling means which are capable of outbound dialing from one PABX of the cluster to another. In Figure 1, a call is being dialed from line 4000 connected to PABX 1A, through PABX 1B, to line 4001 connected to PABX 1C.

Figure 2 is a block diagram illustrating pertinent subsystems of the aforenoted SX-2000 PABX which relate to the present example. However, the arrangement can equally be used with other PABXIS, using the concepts described herein.

The PABX is comprised of a main controller 3 which is in communication with a peripheral unit 5. A station set 7 or other terminating device is connected to the peripheral unit 5 via a line circuit 9. In the SX-2000 PABX, circuit and message switches interface the main controller 3 and the peripheral controller, but the exact manner of control of the peripheral controller and of the station set need not be described as this will be understood by persons skilled in the art, and is not 5 critical to the operation of the arrangement.

The main controller normally operates a program stored in a random access memory (RAM) 11, which program performs call processing, including dialed digit translation to a called line location or to an outgoing trunk, seizing and ringing the called line, monitoring for the call to be answered, etc. The operation of the program is shown as process 13. The digit translation portion is shown as process 15.

In the particular example being described, the RAM 11 or another RAM 11A contains a database 17, which will be described in more detail below.

In operation, when the main controller of PABX 1A (15200) determines that a called line has been dialed, e.g. digits 4001 being dialed from line 4000, it operates the call process 13. The call process causes digit translation, and looks up the dialed digits 4001 in database 17. The data returned from the database is the identity of the remote PABX in the cluster to which the line identified by the dialed number is connected, i.e. PABX 15202, and the line number on the remote PABX. This is shown in Figure 2 as the contantenated number 52024001.

The digit translation continues, to identify an outgoing trunk destined to PABX 1C, and provides the concantenated number to the normal call process 13 whereby normal processing is continued. The main controller 3 then creates a message as shown in Figure 1 in the normal manner, e.g. transmitting the cluster number identification and calling (originating) line 4000 (OLI 594000), transmitting the destination number 6 and PABX number (DA 52024001), and sending it via a trunk and via PABX 1B If necessary to PABX 1C (#5202).

PABX 1C performs the reverse process as will be described below, and rings line 4001.

In the event that the digit translation determines that the destination is on the same PABX 1A as the PABX on which the call originated, the main controller 3 rings the line that the database has indicated corresponds to the called directory number.

Figure 3 illustrates the PABX 1C (which is similar to PABX 1A) carrying out the terminating process. The incoming call is received via trunk circuit 19, the data of which is passed via peripheral controller 5 to the main controller 3, In this case the incoming digit data is as was generated by PABX 1A, i.e.

52024001. The main controller operates the call process 13, looks up 52024001 in database 17A, finds the prefix 05202 designating itself (PABX 1C) and as a result of finding its own 15202 address, strips off the PABX identifier digits 5202 and continues the call terminating process. The digit translation process then reenters digit translation using the remaining digits 4001 to determine the electri6al location of line 4001, and continues with normal call processing to ring the line 4001 via peripheral controller 5 and line circuit 9A.

Figure 4 is a block diagram of database 17 or 17A and shows the lookup process.

A common corporate telephone directory 21 database table contains records 21A having the fields

Name, Telephone Number, Corporate Department, and Location (of the person named). This directory can be filled in and changed by means of a table as shown in Figure 4A 7 In addition to the above, the table contains a Field Type, which is a protected field that indicates whether the corresponding telephone number is local, external or is a remote directory number. The following values may be used for this field:

1. Int: Used for all telephone numbers which translate to local devices, hunt groups, etc.

2. Ext: Used for all telephone numbers which translate to ARS routes, list or plans.

3. A CEID index (e.g. 1 to 999) for remote cluster element devices (remote station apparatus) represented by a remote directory number. 4. Blank, when the corresponding telephone number field is blank.

A remote destination number table 23 contains records having two customer assignable fields, a directory number and a CEID index. The directory number is a programmable field of 1 to 7 digits (including and #) for assigning the directory number of a remote cluster element device (station apparatus). The CEID Index is a programmable field of 1 to 3 digits for assigning the CEID index.

The assignments of the remote directory numbers must conform to the following rules. The specified directory number must translate to a programmed remote directory number, or must not translate to a programmed local directory number. In the latter case, the specified directory number becomes as a remote directory number. Also the CEID index must already be assigned in the cluster element assignment form, to be described below.

This table can be filled in by using a displayed table as shown in Figure 4B. Once this table is filled in or changed by the customer administrator, the 8 directory table 21 is updated, and the additions or changes are visible in the directory shown in Figure 4A.

The local cluster element table 25, which can have an assignment form as shown in Figure 4C, contains records 27 formed of the following fields:

1. CEID Index (Cluster Element Index): a programmable field of 1 - 3 digits for assigning the

CEID index. This number must be in the range 1 - 999 and unique within the table.

2. CEID Digits (Cluster Element Digits): a programmable field of 1 to 7 digits (including and for assigning a cluster element's identification digit string. The CEID digits of remote cluster elements (PABXs) must translate to an ARS (e.g. a trunk) route, list or plan. one of the entries assigns the CEID digits of the local PABX as indicated in the adjacent field.

3. Local Element: a programmable Yes or a blank field. Entering Yes in this field Indicates that the adjacent CEID string represents the CEID digits of the local PAM. There can be only one entry identified as the local cluster element. The local entry is added to the PABX's numbering plan and therefore must be an unique directory number. An example of a local entry is 25 the number 5200. identifying PABX 1A. 4. Text: This Is an optional comment field that can be e.g. 20 characters long, for recording information about the cluster element (PABX). Programming rules for the cluster element assignments are as follows:

1. Each.CEID index must be unique within the table.

If a CEID index is to be deleted from the table, all telephone directory entries must be searched to ensure that the particular cluster element record is not referenced.

9 2. If a CEID index in entered there must be a corresponding CEID digit string. 3. The remote CEID digits must translate to at least one ARS route with identical leading digits.

4. Local CEID digits, if already programmed, must translate to the local cluster element database record.

If not already programmed, the CEID digits must not translate to any local device type.

S. If CEID digits are entered, there must be a corresponding CEID index.

6. Only one cluster element assignment record may be assigned to be local. If already programmed, the CEID digits of the designated local entry must translate to the designated cluster element database record. if not programmed, the CEID digits of the local entry must not translate to an existing internal number.

The records of the cluster element table 25 are thus pointed to by the remote destination number table 23, and thus the index recorded therein are contained in the cluster element table 25 in association with the CEID digits. As noted above, one of the local elements in the table is identified as the identification number of the local PABX number (e.g. 5200.

All PABXs in a cluster have the same primary node identification (e.g. a corporate single general telephone number). A cluster also has an unique numbering plan. Every PABX of the cluster will have an identical telephone directory. Each cluster element (PABX of the cluster) is given an unique identifier, its CEID, This identifier is used by the call process to resolve routing to the appropriate PABX and to aid in the centralized management of the cluster telephone directory.

In operation, therefore, once the database has been completed, the call process having received dialed digits (e.g. 4001) from local telephone set 7 processes through digit tree 29 (Figure 4), and accesses the cluster element table 25 of database 17 (Figure 5). A cluster element record corresponding to the dialed digits is retrieved from the table 25 (index 459), as well as the local PABX number 5200.

The fact that there is no local element indicator in the local element field of the record with index 459 can be used as an indicator that the call is to be terminated at another PABX. In that case, remote destination number table 23 can be looked up to determined the location of the called number, i.e. the remote destination PABX number. In the example shown, index 459 is contained in the record which designates PABX 5202, reference numeral 1C in Figure 1, which is the PABX on which called line 4001 terminates.

In the event that the local PABX 15200 is indicated as the terminating PABX, this information is returned to the call process, which finds the dialed line 4100 locally, and completes the call locally.

In the preferred embodiment being described, a single directory number pool for a cluster of PABXs is used, and a centralized database is maintained which can be downloaded to each PABX of the cluster for use by each PABX to process.calls at intervals depending on when changes to the database have been made. The directory database can be easily updated as needed by filling in the above-described form, which translates to tables identifying which PABXs carry the various lines.

The tables are accessed for digit translation when a call is made to a directory number in the cluster, the appropriate messaging to the correct PABX in the cluster is generated, and the call is routed to the correct PABX in the cluster. The correct record in the table is correlated to the correct PABX by means of the index.

11 A person understanding this invention may now conceive of alternative structures and embodiments or variations of the above. All of those which fall within the scope of the claims appended hereto are considered to be part of the present invention.

For example, although in an embodiment of the invention described above by way of example, the system has been described with reference to telephone numbers, it will be appreciated that the numbers may relate to any peripheral apparatus, for example facsimile, telex or computer apparatus.

12

Claims (11)

1. A method of processing a call within a cluster of PABXs comprising:

(a) receiving a dialed directory number designating a called line within the cluster, (a) accessing a database and obtaining an identity of a terminating PABX within the cluster on which a line corresponding to the dialed directory number is terminated, (b) seizing a trunk, and generating and transmitting a message to the terminating PABX which identifies the terminating PABX and the dialed directory number, (c) at the terminating PABX, recognizing the terminating PABX identification and as a result translating the dialed directory number to an electrical line location, and (c) completing the call on the terminating PABX to the line corresponding to the dialed directory number.

2. A method as defined in claim 1 including preparing a centralized database containing records correlating directory numbers with PAMs on which they terminate, and downloading the database to each of the PAMs within the cluster for use as the database In step (a).

3. A method as defined in claim 2 including changing the PABX location of at least one line on the centralized database, and downloading the database to 13 each of the PABU within the cluster for use as the database in step (a).

4. A method as defined in claim 3 including receiving dialed digits in a PABX, translating the dialed digits including looking up in a downloaded database a called PABX identity on which a line identified by the dialed digits is connected, and in the event the database indicates a terminating PABX carrying a line identified by the dialed digits which is the same as the PABX, completing the call within the PABX originating the call.

5. A method as defined in claim 4 including storing in a table of the database the identity of a local PABX against directory numbers, and using that identity to compare with the called PABX identity to determine whether or not the call is to be terminated on a local PAM.

6. A method as defined in claim 5 in which a table correlating directory numbers with PABX Identification numbers, and in which the table on which the local PABX is identified an well as an indication of whether directory numbers are not local, are related by a common index.

7. A method as defined In claim 7 in which a directory correlating names of subscribers with directory numbers are indexed by said Index.

8. A method of processing a call within a cluster of PAMs comprising:

storina in a database:

14 (I) a first table which relates telephone numbers with indexes to a second table defining the identities of PABXs within the cluster on which called directory numbers are to be terminated, (ii) the second table relating said indexes with identities of said PABXs, (111) a third table which relates said indexes with directory numbers of lines terminating on said PABXs, (b) receiving in an originating PABX in said cluster a set of dialed digits corresponding to a telephone number of a called party, (c) accessing the first table using the set of dialed digits to obtain an index, (d) accessing the second and third tables using said index to obtain an identity number of a terminating PABX on which a called party line is terminated and a directory number of the called party line on the terminating PABX, (e) assembling said identity number and said directory number in a message format and sending the message to said PABX to.complete a call to the called party in a manner as if the message containing said identity number and said directory number had been dialed from an originating line.

9. A method as defined in claim 8 in which at least one identity of a terminating PABX is absent, Identifying the terminating PABX as the same as the originating PABX In the event said identity is absent, and instead of carrying out step (c), processing the call to a line terminating on the originating PABX identified by said directory number.

is

10. A method of processing a call within a cluster of PAWS, as claimed in claim 1 or claim 8 substantially as described herein with references to Figs. 4, 4A, 4B, 4C and 5 of the accompanying drawings.

11. A system for use in processing a call within a cluster of PAWS emplying a method as claimed In any one of the preceding claims.