Note: Descriptions are shown in the official language in which they were submitted.
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FIELD OF THE INVENTION
This invention relates to the field of
telephony, and in particular to a system and method for
providing single portable telephone numbers to users
within a cluster of PABXs.
BACKGROUND TO THE INVENTION
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.
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SUMMARY OF THE INVENTION
In an embodiment 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 accordance with an embodiment of the
invention, a method of processing a call within a
cluster of PABXs is comprised 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 dialed 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 accordance with another embodiment, a method
of processing a call within a cluster of PABXs is
comprised of storing in a database: (a) a first table
which corresponds 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 corresponding the
indexes with identities of the PABXs, (iii) a third
table which corresponds the indexes with directory
numbers of lines terminating on the PABXs, (b) receiving
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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
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.
BRIEF INTRODUCTION TO THE DRAWINGS
A better understanding of the invention will be
obtained by reading the description of the invention
below, with reference to the following drawings, in
which:
Figure 1 is a block diagram of a cluster of
PABXs,
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,
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Figure 4C is a table form for assignment of
cluster element (e.g. station apparatus) directory
numbers to their host PABXs, and
Figure 5 is a diagram used to illustrate an
example of operation of the invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
Figure 1 illustrates a cluster of PABXs lA, lB
and lC, 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 #59. 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 lA,
and extension 4001 associated with PABX lC.
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 lA, through PABX lB, to line 4001
connected to PABX lC.
Figure 2 is a block diagram illustrating
pertinent subsystems of the aforenoted SX-2000 PABX
which relate to the present invention. However the
invention can equally be used with other PABXs, using
the concepts described herein.
The PABX in 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
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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
critical to the present invention.
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 accordance with the present invention, the
RAM 11 or another RAM llA contains a database 17, which
will be described in more detail below.
In operation, when the main controller of PABX
lA (#5200) 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 #5202, 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 lC, 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
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and PABX number (DA 52024001), and sending it via a
trunk and via PABX lB if necessary to PABX lC (#5202).
PABX lC 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 lA
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 lC (which is
similar to PABX lA) 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 lA, i.e.
52024001. The main controller operates the call process
13, looks up 52024001 in database 17A, finds the prefix
#5202 designating itself (PABX lC) and as a result of
finding its own #5202 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 electrical 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 in accordance with an
embodiment of the invention.
A common corporate telephone directory 21
database table contains records 2lA 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
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.
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
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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 PABX. 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
the number 5200, identifying PABX lA.
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.
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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 rout 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.
5. 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
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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 lC in Figure 1, which is
the PABX on which called line 4001 terminates.
In the event that the local PABX #5200 is
indicated as the terminating PABX, that PABX number is
compared with the PABX number 5200 indicated in table 25
as being the local PABX. In that case this information
is returned to the call process, which finds the dialed
line 4100 locally, and completes the call locally.
In the preferred embodiment of the invention 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
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in the cluster. The correct record in the table is
correlated to the correct PABX by means of the index.
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.
