Note: Descriptions are shown in the official language in which they were submitted.
CA 02224023 1997-12-OS
VIRTUAL WIDE AREA CENTREX
Field of the Invention
This invention relates to telecommunications
Intelligent Network call routing via SS7 signalling from a
network of switches, but more particularly to a method of
providing an improved Wide Area Centrex service such that
feature transparency is achieved across a plurality of
central office switches, each serving one or more customer
locations.
Description of the Prior Art
Centrex Service is a widely deployed generic
business offering which provides customers with features
that are normally associated with PBXs (Private Branch
Exchanges). Whereas a PBX is located on a customer's
premises, and is generally connected to other PBXs in the
area via leased facilities, Wide Area Centrex service is
provided from a Telco's central office premises and serves
the area (generally an entire city) via various local and
remote serving facilities. The services offered by Centrex-
capable central offices are shared with other business
customers as well as with the PSTN (Public Switched
Telephone Network), thus offering an extremely cost-
effective solution to private switching and value-added
services.
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Customers having several service centers or
locations within an Exchange, but which are distributed
among several central office serving areas, i.e. with
different NXXs, are customarily served at all locations from
a single central office, for example, the CO that serves the
main site. The remaining sites are then served by digital
remote concentrators that are homed on the main CO. This
arrangement allows all the customer's locations to be served
by a single NXX, which becomes, in effect, a private
Numbering Plan that can be administered by the customer.
In order to achieve a Private Numbering Plan which
can be administered by the customer, as well as to avoid
certain feature transparency issues, it is customary to
serve all of a particular customer's locations from a single
central office switch. The major shortcoming of this
serving arrangement is the cost of deploying remote serving
arrangements, generally consisting of remote switch
peripherals attached to the main serving central office
switch via dedicated high-speed transmission facilities.
The cost of such non-standard facilities is such that - in
addition to increasing the basic provisioning cost - the
service cannot be economically provided to all locations.
This is a major irritant for customers, particularly those
with a large main office and many small branch locations
within a city.
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In recent years, with the advent of the
Intelligent Network, a number of potential solutions have
been proposed for portions of the service, such as routing
using a database.
One such solution is described in U.S. Patent
Number 4,191,860, issued Mar. 4, 1980, to Roy P. Weber.
This and a number of subsequent patents have dealt with
inward call routing, primarily for 800 number type calls.
Those related to Centrex database applications have
generally dealt with enhanced vertical feature
functionality - e.g., speed or repertory dialing,
centralized message detail recording , automatic call
routing, person locator services. Only the following two
patents attempt to address the need identified above.
U.S. Patent Number 5,247,571, issued Sept. 21,
1993, to William A. Kay et al., discloses a method "for
providing private network service features to business
customers with facilities at a number of geographically
diverse locations through the public telephone network."
However, this patent focuses on extracting intelligence from
the network switches and vesting it in a central database.
The intent appears to be to reduce or eliminate switch-
vendor-provided software by providing equivalent
functionality in a central database under the control of the
Telco. Aside from moving some network intelligence from a
plurality of switches to a central database, this patent
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offers only a limited and somewhat questionable capability
for Private Numbering Plan administration.
In general, the method achieves benefits by
bringing the Centrex station features, translations, and
data recording from all the individual switches to a central
database where they can be more readily accessed or modified
by the customer. With respect to numbering plan
administration, the best mode for carrying out the invention
is revealed as abbreviated dialing, a private "location
prefix" being required to avoid number conflicts amongst
switches. However, a split Customer Number Access/Network
Node Address (CNA/NNA) scheme - identified in the Kay patent
as "private number"/North American Numbering Plan (NANP)
number - is proposed as an alternative to the abbreviated
number scheme and is identified as "Portable Intercom Number
Dialing."
There appear to be at least two serious
shortcomings to this scheme: i) internal callers can use
the private number to reach an internal extension but
external callers must use the NANP number to reach the same
extension; ii) terminating features that need to identify
the calling party, such as Integrated Voice Messaging
Systems (IVMS) will receive the NANP instead of the private
number, making it difficult for internal users to recognize
calls from other internal users.
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U.S. Patent Number 5,422,941, issued Jun. 6, 1995,
to George Hasenauer et al., expands on the method of U.S.
Patent Number 5,247,571 by addressing a serious shortcoming
identified by switch vendors: using a central database for
Private Numbering Plan administration and also for the
provisioning of vertical Centrex features (e. g., call
transfer, conferencing) "causes feature conflict problems."
The invention reveals a method of resolving the conflicts by
introducing two separate translation steps, one in the
switch and the other at the SCP. As such, this second
patent is merely a technical refinement of the first and
introduces nothing new in terms of capability. "Portable
Intercom Number Dialing" is elevated in importance and given
a feature name but retains the shortcomings identified
1 5 above .
Neither of these patents addresses the fundamental
issue of making a plurality of central office switching
systems, each at a different physical location, operate as
if they were a single switch. The melding is not seamless,
imposing operations or conditions which are not present when
service is provided from a single switch: either the user
is required to dial a location prefix to identify the target
switch or there is an awkward mixing of private and public
numbers. In the first instance, users should not be
required to know which network switch serves a particular
Centrex station. In the second, a user should only need to
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remember one number - if a short intercom number is to be
introduced, it should be an abbreviation of the public
number (typically the last three, four, or five digits), and
not a totally different number.
Summary of the Invention
There remains a need for providing a Centrex type
service which extends functionality to a plurality of
central office switches in a manner that is transparent to
the user.
It is therefore an object of the present invention
to provide Virtual Wide Area Centrex (VWAC) in which there
is a total separation of the telephone numbers seen and used
by customers (Customer Number Address - CNA) from the
telephone numbers used internally by the network for call
routing purposes (Network Node Address - NNA), such that
there are two separate and distinct numbering plan domains.
The most significant digits of the telephone
number normally associated with the customer, per the North
American Numbering Plan - typically the NPA NXX - form the
most significant digits of the CNA. The remaining digits of
the CNA - typically four - are administered by the customer.
With respect to the NNA, each geographic location has an
unique NPA NXX, generally one currently associated with the
serving switch. The remaining digits of the NNA are
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randomly assigned to subscribed Centrex stations by Telco
personnel and are of no consequence to the customer.
In essence, what is being disclosed is a multi
switch network deployment of an internal switch design
concept, wherein numbers seen and used by customers are
different from those used internally by the switch. The
former are Directory Numbers (DNs) whereas the latter are
commonly called Line Equipment Numbers (LENS). With respect
to operation of an individual switch, only Telco operations
personnel need to know the LEN, and, similarly, in a VWAC
environment, only Teleco operations personnel need to know
the NNA.
Another object of the present invention is to
provide VWAC services which make use of a central database -
typically an SCP - to translate CNAs to NNAs and vice versa
of stations served by Centrex type services.
A further object of the invention is to provide
dynamic control of the numbering plans through the central
database so that users may readily move from one location to
another while retaining their CNAs. Further enhancements,
to be discussed later, make it possible for users to move
from one physical location to another as quickly and easily
as wireless users may change location.
In accordance with an embodiment of the present
invention, there is provided a method of providing Wide Area
Centrex to a telephone network having a plurality of
CA 02224023 1997-12-OS
switching offices capable of providing traditional Centrex
station features (e. g., call transfer, conference bridging,
multiple appearance directory number, "Ring-Again"/Automatic
Callback), and of supporting SSPs (Service Switching Points)
operating with AIN (Advanced Intelligent Network)
application software. The method comprises the steps of:
assigning, as switch-resident datafill by Telco
personnel at Centrex network setup time, a "real"
telephone number to each subscribed station at the
customer sites, this being the NNA;
assigning, on an ongoing basis by the Telco or by the
customer, an abbreviated "virtual" telephone number to
each active station (i.e., a station with a specific
assigned user) at the customer sites, this being the
least significant digits of the CNA;
assigning, as switch-resident datafill by Telco
personnel at Centrex network setup time, a Business
Group ID (BGID) to each subscribed station at the
customer sites, this ID serving to imply the most
significant digits which are missing from the
abbreviated CNA (typically the NPA NXX);
treating the called number for all originating calls,
whether dialed by a Centrex user or received from the
PSTN (Public Switched Telephone Network), as a CNA;
connecting each central office to a central database -
i.e., an SCP (Service Switching Point) - this database
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having a number translation capability to map CNAs into
NNAs and vice-versa;
assigning, as switch-resident datafill by Telco
personnel at Centrex network setup time, AIN trigger
datafill such that at least some Centrex related calls
generate queries to the central database if certain
criteria are met;
at the database, translating the BGID plus the called
abbreviated CNA into an NNA to determine how to route a
call to a station at any one of the customer sites
served by the Centrex type services;
at the database, translating an originating, switch-
supplied Centrex Calling Line ID (CLID) from an NNA to
a CNA prior to authorizing the switch to execute call
completion, either to an internal Centrex station or to
the PSTN, such that Centrex, CLASS, or IVMS features at
each destination receive a network-dialable number
allowing them to work as they did prior to the present
invention;
after a called number translation, at the switch that
launched the query, setting a Conversion Flag (i.e., a
traveling class mark) on the call to indicate that the
called number has been converted from a CNA to an NNA;
at the terminating switch, with the aid of the
aforementioned Conversion Flag, ensuring that no call
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can be terminated at a Centrex station unless the
called number has been converted to an NNA;
connecting each central office to a high-speed data
router - i.e., an STP (Signalling Transfer Point) -
such that "connectionless" data messages - i.e., SS7
TCAP messages - can be routed from one network node to
another;
assigning, as STP-resident datafill by Telco personnel
at Centrex network setup time, appropriate GTTs (Global
Title Translations) such that TCAP queries from the AIN
triggers related to the Wide Area Centrex service are
routed to the appropriate SCPs, and that TCAP end-to-
end messages for various Centrex features are first
routed to a Signalling Processor Adjunct (SPA);
at the aforementioned Signalling Processor Adjunct,
performing a 10-digit translation of a CNA into the DPC
for the destination switch, and the translation of the
calling or called number fields in the SS7 TCAP message
from a CNA to an NNA, or vice-versa, as required by
specific end-to-end service features;
providing a database administration system - i.e., a
Service Management System (SMS) - to receive numbering
plan changes from the customer, create and assemble the
necessary network service orders, forward these service
orders to the SCP and the Signalling Processor Adjunct,
and save master copies;
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providing an outboard processor, having an internal
lookup database that is kept current by the SMS, to
convert switch-based operational measurement data such
as SMDR from NNA to CNA prior to their being presented
to the customer.
Brief Description of the Drawings
The invention will be better understood by an
examination of the following description, together with the
accompanying drawings, in which:
Fig. 1 is a block diagram of the main elements
forming part of a prior art telephone network offering a
form of Wide Area Centrex that ensures complete feature
transparency across a plurality of geographically diverse
customer locations;
Fig. 2 is a block diagram of the main elements
forming part of a telephone network offering Virtual Wide
Area Centrex according to the present invention;
Figs. 3a and 3b are flow charts illustrating how
calls generated from a Centrex station are handled in an
originating switch;
Fig. 4 is a flow chart illustrating how calls from
other Centrex switches and from the PSTN are handled in a
terminating switch; and
Fig. 5a and Fig. 5b are translation tables for use
with the network of the present invention
CA 02224023 1997-12-OS
Description of the Preferred Embodiments
In order to lighten the following description, the
following ronyms will be used:
ac
AIN: Advanced Intelligent Network;
BGID: Business Group Identification;
CCS7: Common Channel Signalling 7;
CLID: Calling Line Identification;
ClgPn: Calling Party Number;
CNA: Customer Number Address;
DN: Directory Number;
DTMF: Dual Tone Multi-Frequency;
GAP: Generic Address Parameter;
GTTs: Global Title Translations;
IAM: Initial Address Message;
IEC: Inter-Exchange Carrier;
IN: Intelligent Network;
ISDN: Integrated Services Digital Network;
ISUP: ISDN User Part;
IVMS: Integrated Voice Messaging Systems;
LENS: Line Equipment Numbers;
MBG: Multi-switch Business Group;
NANP: North American Numbering Plan;
NNA: Network Node Address;
PBXs: Private Branch Exchanges;
PIC: Primary Interexchange Carrier;
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PNP: Private Numbering Plan;
PSTN: Public Switching Telephone Network;
SCP: Signalling Control Point;
SMS: Service Management System;
SSPs: Service Switching Points;
SS7: Signalling System 7;
STP: Signalling Transfer Point;
TCAP: Transaction Capabilities Application Part;
and
VWAC Virtual Wide Area Centrex.
The networks shown in Figs . 1 and 2 do not show,
for sake of clarity, all elements normally associated with
SS7 messages. A typical SS7 network consists of signalling
links and nodes. SS7 nodes are referred to as Signalling
Points (SP) and are interconnected by signalling links.
Each SP is assigned a unique point code, serving as the
network address for message routing. SS7 Signalling Points
(SP) include Service Switching Points (SSP), Service Control
Points (SCP), and Signal Transfer Points (STP). Persons
skilled in the art to which the present invention pertains
are assumed to be familiar with conventional SS7
functionality, AIN application fundamentals, as well as
basic Centrex features and functions.
Services Switching Points (SSPs) are associated
with SS7 equipped switching offices. Their prime function
is to serve as a source and destination for messages related
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to the calls they handle. Outgoing messages (i.e., queries)
destined for SCPs are formatted in accordance with the SS7
Transaction Capabilities Applications Protocol (TCAP).
These messages are triggered at various points during call
processing, on some or all calls, if various criteria are
met - for example, combinations of a particular calling
station, a particular called number (or portion thereof), or
a particular incoming trunk group. Call processing is
suspended until a response, also in TCAP format, is received
from the SCP, whereupon call processing either simply
ignores the response and continues, proceeds using SCP-
modified call data, or is aborted.
Service Control Points (SCPs) are often referred
to as databases in that lookups of calling and called
numbers are among the most frequently performed functions.
Through the use of "service logic," SCPs can also serve as
centralized sources of network intelligence by determining
how calls are to be routed through the network. Queries and
responses to and from the SCP utilize the aforementioned
TCAP, and appear as data packets with source and destination
addresses in the form of point codes.
Signalling Transfer Points (STPs) are high-speed
data routers which provide a packet switching function
amongst other nodes in an SS7 network. They examine
incoming messages for a point code and then use this to
select an appropriate SS7 link to carry the message to the
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destination node. Three important functions of an STP are
i) to act as a tandem point for signalling links so that
every node in the network does not have to be linked to
every other node; ii) to provide a gateway for SS7 network
interconnection to screen out unauthorized access; and
iii) when so requested, to do a database lookup on the
called number and overwrite the original destination point
code. This latter function, called Global Title Translation
for TCAP applications, is service-specific, the specific
service being identified by a 3-digit Service Subsystem
Number (SSN). This third function of an STP is used by
certain enhanced station-to-station Centrex features in the
prior art as well as in VWAC.
Service Management Systems (SMSs) provide a master
database for all network data needed to specify a particular
service. The SMS is also responsible for formulating and
delivering service orders for all other network nodes,
particularly SCPs and STPs, such that the specified service
configuration is realized.
The SS7 messages transmitted between the SSP and
the SCP are formatted in accordance with TCAP, as mentioned
above, which provides standardized formats for various query
and response messages. Each query and response includes
data fields which contain a variety of information about a
call in progress. Of particular importance to the present
invention are the fields containing the calling and the
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called telephone numbers. The calling number is generated
by the SSP, as soon as a station goes off-hook, in that the
CLID for each station is part of the switch's Telco-
provisioned datafill. The called number, on the other hand,
represents the digits that a user has just entered on a dial
pad to set up the call in progress . Also important in the
current context is a Service Indicator and a Trigger
Identity so that the TCAP query can be routed to the
appropriate AIN SCP, and this SCP can select a query
processing routine from amongst a plurality of such
routines. In addition to providing modified call data,
responses also contain an instruction to the SSP on what to
do with the response and how to proceed with the call.
Fig. 1 shows a prior art telephone network
offering Wide Area Centrex to a number of remote customer
sites.
When customers have several locations within an
Exchange, but which are distributed among several central
office serving areas - historically known as wire centers -
it is customary to serve all the locations from a single
central office. Generally, this is the central office that
serves the customer's main site. The remaining sites are
then served by remote digital concentrators that are homed
on the main switch via dedicated high-speed transmission
facilities. The object of this costly configuration is to
provide seamless feature functionality across all the
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stations, particularly with respect to administration of the
Private Numbering Plan.
For example, in Fig. 1, the main site 10 of a
Centrex customer is served by a central office 11 which
provides Centrex functionality to other sites, remotely
located away from the serving area 12 of central office 11.
In Fig. 1, the other sites are depicted at reference
numeral 13 for site 1, 14 for site 2, and 15 for site 3.
All central offices are connected to the PSTN 16 and all
sites in this example are located within the same exchange.
That is, all sites are part of the same local calling area.
It is to be noted that although each site forms part of the
PSTN 16, they are shown separately to illustrate the
concepts of Wide Area Centrex. That is, each central office
19a, 19b and 19c is also used for non-Centrex customers and
thus each is shown connected to the PSTN 16. It should be
noted that the centrex customers at location 13, 14 and 15
are all served by central office switch 11 via remote line
peripherals, i.e. such as concentrators 22a, 22b and 22c.
Note that the concentrators would actually be physically
located with switching offices 19a, 19b and 19c
respectively.
With existing Wide Area Centrex services, each
site which is located within the same exchange, can be
reached using a single NPA NXX. (For the sake of
simplicity, reference to the NPA will be~omitted in the
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CA 02224023 1997-12-OS
description which follows.) For example, station 17 can
reach any Centrex site using the NXX 567, even though the
remote sites are located in areas served by central offices
with different NXXs. On the other hand, non-Centrex
telephone stations in the site 1 serving area are normally
assigned telephone numbers with the NXX of 234, site 2 with
an NXX of 789, site 3 with an NXX of 456, and the main site
with an NXX of 567.
When a caller at Centrex station 20 wishes to
reach another Centrex station, he or she can simply dial the
"intercom" number, typically the last four digits of the
Private Numbering Plan, to complete the call. Calls to non
Centrex stations are recognized by full-length (i.e., 7 or
10-digit) called numbers that are prefixed by an "escape"
code, typically the digit 9. If no escape code is used,
then the call becomes an intra-Centrex call, wherein
(typically) four digits are used to route the call, the
missing digits being implied by a Business Group ID (BGID)
assigned to the station by Telco personnel at Centrex
network setup time. In this example, if a caller at Centrex
station 20 wished to reach Centrex station 21 of site 2,
digits 4567 would be dialed at station 20. The digits would
be received by central office 11 via remote concentrator
22a.
For non-centrex calls, a caller at station 17 who
wishes to reach station 18 served by switching office 19a
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from the public switched telephone network (PSTN) 16 would
dial 234-XXXX. Any call to a station with an NXX of 234
would be routed the same way. Similarly, calls to stations
having an NXX of 789 and 456 will be routed via switching
offices 19c and 19b, respectively. On the other hand, a
caller at station 17 wishing to reach station 20a of the
centrex customer located at site 1, would dial the centrex
customer's published number, i.e. 567-1234 even though the
actual physical address of station 20a is 234-XXXX. When
the call is made, the 567-1234 digits would be received at
central office 11, which is the main centrex service site.
Central office 11 would determine from the last four (4)
digits that the called station is located on site 1. The
call would then be routed via concentrator 22a to station
20a.
When a caller at station 20a wishes to reach
another centrex station, the caller can simply dial the
extension number or last 4 digits of the private numbering
plan to complete the call. If an escape code, such as
digit 9, is dialed, the call is treated as a normal call
through the PSTN, but via central office 11 and not
switching office 19a. If no escape code is used, then the
call becomes a centrex type call, wherein the 4 digits are
used to route the call. In this example, if a caller at
station 20a wishes to reach station 21 of site 2, digits
3456 would be dialed at station 20a. The digits would be
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received by central office 11 via concentrator 22a and the
call routed to station 21 via concentrator 22b. Even if a
caller at station 20a wishes to call a station located on
the same location, for example, station 20b, the call would
still be routed via concentrator 22a to switch 11 and back
again to station 20b.
Thus, this arrangement allows all customer
locations to be served by a single NXX, which becomes, in
effect, a Private Numbering Plan that can be administered by
the customer. As can be seen, although most of the
fundamental business needs are met, this solution is costly
to deploy, inefficient, and not available to locations with
small numbers of lines. Thus, it is an irritant for
customers with a large main office and many small branches
within a city, the major banks exemplifying this type of
customer. For example, if a remote site has 20 lines
required for Centrex services, a concentrator with a minimum
cost-effective capacity of 150 lines is the best that can be
offered. The customer is thus paying for a system which has
a much higher capacity than is required.
Referring now to Fig. 2, the block diagram
illustrates the network elements required to provide a
Virtual Wide Area Centrex according to the present
invention. As in Fig. 1, the customer requires a Wide Area
Centrex service amongst a main site 30 and three remotely
located sites, i.e., sites 1,2, and 3. In Fig. 2, instead
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CA 02224023 1997-12-OS
of making-use of concentrators and dedicated facilities, the
main site 30, and remote sites 1 , 2 and 3 are connected to
each other via their respective Central Office (CO) and
PSTN 16. However, with the network of the present
invention, the telephone numbers associated with a
customer's Centrex service are assigned a virtual (typically
a 4-digit) Private Numbering Plan number, with total
separation of the virtual customer network address (CNA) and
real network node address numbers (NNA). That is, the
customer network address is a virtual telephone number used
within the centrex network and outside thereof to reach
another centrex subscriber station. On the other hand, the
real network node address is used by the network to route
calls internally and externally of the centrex network. The
NNA is not meant to be visible by the centrex subscriber but
is used to identify a physical, i.e. real address associated
with the dialed CNA.
The translation from virtual to real, and vice
versa, takes place at an SCP 31, allowing remote Centrex
stations to be served from any central office capable of
launching SS7 messages to the SCP. Costly remote
concentrators can then be removed or re-homed; small
locations, not previously accessible, can then be served
cost-effectively on ordinary lines from their nearest
central office. As indicated above, not all SS7 network
elements are shown for sake of clarity. For example,
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CA 02224023 1999-11-09
although dashed lines are used from the central offices of
each site directly to the SCP 31, the links could also be
accomplished via STPs.
To set up a network according to the present
invention, the NNAs are made identical to the non-
abbreviated versions of the original Centrex station
telephone numbers, or to the PSTN numbers of those former
non-Centrex stations which can now be accommodated in a Wide
Area Centrex solution. With respect to the CNAs, the NXX of
the CNA is made identical to the original NXX of the main
site - 567 in the Fig. 2 example. To minimize number
changes and service disruption, the last four digits of the
CNAs for users at the main site are made identical to the
last four digits of their original Centrex station numbers.
Users at sites 1, 2, and 3 are assigned CNAs from spare
numbers in the 567 NXX, resulting in number changes at these
locations. A number translation matrix for use with the
present invention is disclosed in applicant's United States
Patent No. 5,553,130 entitled NUMBER TRANSLATION SERVICES
MATRIX, which issued on September 3, 1996.
Before discussing call flows in detail, a high-
level description of how calls are routed to and from the
PSTN is provided as this represents a departure from the
prior art . In one embodiment of the invention, for a call
from a Centrex station to a PSTN station, say from calling
station 20 to called station 17, an escape code (e.g., the
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digit 9) is recognized by central office 19. The call is
then routed directly into the PSTN, thence to station 17,
which is consistent with prior art solutions for Wide Area
Centrex. In another embodiment of the invention, all calls
from a centrex serviced telephone network device, regardless
of whether they contain an escape code or not, trigger a
query to the SCP 31 . The advantages of sending a query to
the SCP for each call will be described further below.
For a call in the reverse direction, where
station 17 initiates the call, the routing is necessarily
indirect. This is because, as mentioned earlier, the
dialed number is treated as a virtual number, i.e. CNA upon
entering the Centrex network. In the example at hand, the
PSTN routing recognizes the called 567 NXX as belonging to
central office 11 and routes the call there. A database
lookup is then done by switch 11 to translate the CNA into
an NNA, whereupon it is recognized by switch 11 that the
call should be routed to central office 19 and completed to
Centrex station 20.
The call flows are now examined using the network
configuration of Fig. 2 and the call flow diagrams of
Figs. 3a and 3b and Fig. 4. A number of different AIN
triggers can be used in accord with the present invention.
For the Figs. 3a and 3b flow diagrams, the Individual Dial
Plan (IDP) trigger is used. For the Fig. 4 flow diagram,
the Terminating Attempt (TA) trigger is used. Triggers can
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CA 02224023 1997-12-OS
be either "assigned" or "office". With an "assigned"
trigger, any call transversing the switch encounters the
trigger.
As the call progresses through the trigger check
point, the criteria for that trigger is checked. The
criteria, which can be established by a service order data
fill, can include a specific line, trunk, dialed number,
etc. If a match is found for the criteria, the query is
sent to the SCP. If no match is found, the call continues
to progress until another check point is encountered. As in
this example, the assigned trigger is a particular number,
and if the dialed number matches the number assigned in the
trigger, a query will be automatically sent to the SCP.
In the example of Figs. 2, 3a and 3b, an internal
Centrex call originates at station 20 and terminates at
station 21.
Following collection of the dialed digits 40 at
switch 19, call processing encounters an AIN trigger 41 that
has been pre-assigned to station 20 by Telco personnel. As
described above, if the collection of all the expected
digits meets the trigger's criteria, the SCP is accessed 41.
In Fig. 2, a TCAP query is formulated at CO 19. This TCAP
query includes the called number, i.e. 5678 CNA of
station 21 and calling line ID of station 20, i.e. NNA 234-
4567. As will be described below, the SCP performs 2
translations, i.e. one for the called number and one for the
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CLID of the calling party. This is because the CNA is a
virtual number used only by the subscriber and the NNA is
used by the network for routing the calls. At the SCP, a
database lookup 42 is done using the switch-supplied NNA
from the CLID field as a key. If the NNA lookup yields no
CNA (i.e., no user has been assigned to the station) 43,
then the number of the customer's Private Numbering Plan
administrator is substituted for the called number 44.
Assuming an originating NNA with a valid CNA is assigned,
the first digit of the called number is examined for the
escape code 45. As this is an internal call, there is no
escape code and a database lookup 46 is done using a
composite of the BGID and the dialed CNA number as a key.
If the CNA is found to be invalid ( i . a . , not assigned to a
station), the SCP returns a treatment code; otherwise, the
SCP translates the CNA into an NNA 47 and inserts it into
the called number field. The translated number is tested 48
to ensure it is not the customer's PNP administration
center - if it is, the SCP service logic bypasses conversion
of the switch-supplied CLID. Otherwise, the CLID is
translated from an NNA to a CNA 49 and inserted into the
calling number field. It is necessary to translate the
switch-supplied CLID from an NNA to a CNA 50 so that the
called party receives a number that can be called back.
Switch 19 receives the response from the SCP and
deals with a treatment code 52, if any, by aborting the call
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CA 02224023 1997-12-OS
in the indicated manner. Otherwise, it overwrites the
called and calling numbers with data from the appropriate
fields in the SCP's response 53. The Conversion Flag is set
54 so that the call will complete to the destination without
being presented again to the SCP for number translation.
Normal call processing is then executed 55: If the called
NNA indicates an internal call, the switch executes normal
Centrex call processing; otherwise, it routes the call to
the Centrex switch serving the remote location, this being
identified by the NXX digits of the called NNA.
With reference to Fig. 2, whereas CO 19 would
normally establish a call set-up with using the CNA of
station 21 and NNA of station 20, with the method of the
present invention, when a response is received from SCP 31
at CO 19, an Initial Address Message (IAM) containing the
NNA of station 21 and CNA of station 20 is transmitted to
CO 23. The NNA of station 21 being the real address enables
the PSTN network to route the call, whereas the CNA of
station 20 enables station 21 to determine the identity of
the caller and number required to call to return the call if
necessary. When received at CO 23, the call path with
station 21 will be completed. The CLID of station 20, i.e.
CNA will be provided to the called station 21 . The CNA of
calling station 20 is provided instead of the NNA since that
is the call back number that has to be used.
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Referring again to Figs. 3a and 3b, the following
paragraphs describe a call that originates at Centrex
station 20 and terminates at station 17 in the PSTN.
Following collection of the dialed digits at
switch 19, call processing encounters an AIN trigger 40 that
has been pre-assigned to station 20 by Telco personnel.
Collection of all the expected digits meets the trigger's
criteria and the SCP is accessed 41. At the SCP, a database
lookup 42 is done using the switch-supplied NNA from the
CLID field as a key. This NNA belongs to the calling party.
If the NNA lookup yields no CNA (i.e., no user has been
assigned to the station) 43, then the number of the
customer's Private Numbering Plan administrator is
substituted for the called number 44. Assuming an
originating NNA with a valid CNA assigned, the first digit
of the called number is examined for the escape code 45.
Since the called number is preceded by the escape code, 9,
the subsequent digits are an external destination telephone
number and do not need to be translated. However, it is
necessary to translate the switch-supplied CLID from an NNA
to a CNA 50 so that the called party receives a number that
can be called back. As the calling CNA identifies a
specific user, network access privileges are screened 51 to
determine the user's authorization to make toll, overseas,
or other types of expensive calls. If the type of call is
not allowed, the SCP returns an appropriate treatment code.
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Thus, by verifying the presence of an escape code at the
SCP, unauthorized calls made via the PSTN may be blocked or
screened based on the service privileges of the subscriber
using that telephone. If no such screening is required, the
use of an escape code may be identified at the CO 19 instead
of the SCP 31.
Switch 19 receives the response from the SCP and
deals with a treatment code 52, if any, by aborting the call
in the indicated manner. Otherwise, it overwrites the
calling number with data from the appropriate field in the
SCP's response 53. The Conversion Flag is set 54, although
it is not normally used on a call to the PSTN. Call
processing resumes 55 and the call is routed to the PSTN 16,
and ultimately to station 17.
Referring to Fig. 4, calls that originate at
stations in other switches and are received on a trunk at
Centrex switch 11 will now be described. The first
paragraph describes a call from a Centrex station, the
second and third a call from PSTN station 17 destined for
Centrex station 20, and the fourth deals with invalid
scenarios.
The call flow of Fig. 4 is picked up at the point
where the process described in Figs . 3a and 3b resulted in
the originating Centrex switch establishing a trunk
connection to terminating Centrex switch 11. The digits are
collected by the terminating switch 70 and the terminating
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CA 02224023 1997-12-OS
trigger criteria of 71 and 72 are tested. Since the called
NNA is a Centrex station at the switch and the Conversion
Flag is set, the switch executes normal Centrex call
processing to the terminating station.
Assuming now that a call has originated in the
PSTN, the call flow is picked up at the point where a trunk
connection has been established between the PSTN and
switch 11. (Generally, all calls from the PSTN to the
Centrex NXX are presented to switch 11 because the NPA NXX
of the called CNA is a valid, non-ambiguous NANP destination
pointing to this switch.) In this case, the terminating
trigger criteria are met because the called number falls
into the range of VWAC stations and the Conversion Flag is
not set. (Because a called number from the PSTN is virtual
and not real, the switch cannot complete the call to a
Centrex station - a translation of the called number from a
CNA to an NNA is mandatory.) Because the trigger criteria
have been met, a query is launched to the SCP 74. The SCP
does a database lookup on the called number and if there is
an assigned NNA, this is placed in the appropriate response
field. Otherwise, the SCP returns a treatment code.
Switch 11 receives the response from the SCP and
deals with a treatment code 77, if any, by aborting the call
in the indicated manner. Otherwise, it overwrites the
called number with data from the appropriate field in the
SCP's response 78 and sets the Conversion Flag 79. Call
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CA 02224023 1997-12-OS
processing resumes 73, upon which it is determined that the
call should be forwarded to Centrex switch 19 and thence to
station 20.
Finally, there are the cases where the NNAs are
dialed directly, which is inappropriate as they are
irrelevant to the customer and its station users. Referring
to Fig. 2, the CNA for Centrex station 20a is 567-1234
whereas its NNA is 234-4567. Say PSTN station 18, which is
also served by switch 19, dials 234-4567. Although this is
an intra-switch call, it still encounters the terminating
trigger for Centrex station 20 and meets that trigger's
criteria, thereby launching a query on the SCP. A database
lookup is done, assuming the called number is a CNA,
whereupon it is found that there are no valid conversions in
the database for the 234 NXX. Consequently, a treatment
code is returned. (In fact, in this example, 234-4567 has
been reserved for Centrex use and therefore is a "no such
number" in the PSTN.) For the second example, say PSTN
station 17 dials 234-4567. The PSTN routes this call to
switch 19, whereupon it enters the call flow described in
Fig. 4. Because the number is in the Centrex range and the
Conversion Flag is not set, 71 and 72, a query is launched
to the SCP. Again, a database lookup is done, assuming the
called number is a CNA. Again, it is found that there are
no valid conversions in the database for the 234 NXX and a
treatment code is returned.
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As stated earlier, in order to work properly,
terminating features such as Caller ID, Call
Return/Automatic Callback/Ring-Again, and some types of IVMS
must capture telephone numbers which, when returned, will
reach the original calling party. This means that if a call
is received from a caller with a virtual number (i.e., a
CNA), then it is the virtual number that must be captured
and not the traditional switch-supplied CLID. The call
flows described in Fig. 3 and Fig. 4 meet this requirement.
Fig. 5a and Fig. 5b show the necessary database tables.
Fig. 5a represents the more conventional translation of a
virtual called number into a real one for network routing.
Fig. 5b, on the other hand, represents a "criss-cross" table
wherein the switch-supplied CLID is translated into a
"dialable" CLID. Note that one table is the mirror image of
the other, the search key and the record being interchanged.
Thus, given this similarity, both tables can be updated from
a single service order.
As a final note, it is necessary to convert
switch-based operational measurements pertaining to Centrex
stations from NNA to CNA since the former have no meaning to
the customer. Station Message Detail Recording (SMDR) data
is a prime example. This conversion can be done via an
outboard processor having an internal lookup database that
is kept current by the SMS.
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CA 02224023 1997-12-OS
The following deals with variations to the
preferred embodiment, as well as some novel capabilities.
First off, routing variations for incoming calls
from the PSTN are possible and may be desirable. In the
above description, all incoming calls are routed to the
switch serving the main site 11. Remembering that this
solution is targeted at customers with a large main site and
numerous geographically diverse smaller ones, this is a good
strategy. However, an analysis of traffic patterns might
suggest, for example, that calls to the VWAC from the east
end of the PSTN (see Fig. 2) are best routed to switch 19
instead of switch 11. In other words, a switch in the east
end of the PSTN receives a call destined for the 567 NXX,
but instead of routing it to CO 11 routes it to CO 19. This
is a good strategy provided that the majority of Centrex-
destined calls originating in the east end of the PSTN are
indeed destined for Centrex stations served by switch 19.
Currently, the industry is considering Conversion
Flags for other purposes such as Local Number Portability.
However, in the absence of such a flag, the functionality
can be emulated in the SCP by doing a lookup on the switch-
supplied CLID prior to CLID conversion. If the CLID is from
a Centrex station, it can be assumed that the Conversion
Flag is set; otherwise, it is not set.
A particularly important novel capability is the
ability for users to change physical location at will,
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CA 02224023 1997-12-OS
including the ability to move from any customer geographic
location in the VWAC to any another. With prior art, this
has been a major administrative expense, both for the
customer and the Telco. It has also been disruptive to the
customer's ongoing business as office moves have resulted in
long periods of substandard telephone service. The VWAC
solution solves the problem, as follows.
If a user (or an unauthorized person) attempts to
make a call from an unassigned location, that call is
automatically routed to the customer's PNP administrator
without conversion of the switch-supplied CLID (which is an
NNA). Alternatively, if a user moves into a new office and
then calls the PNP administrator, the CLID on that call is
not converted from an NNA to a CNA (refer to Fig. 3). In
either case, the administrator receives a call in which the
CLID identifies the caller's station (i.e., the caller's
physical location, as opposed to the caller's identity).
The caller provides his or her identity (i.e., the CNA) and
a Personal Identification Number (PIN). Assuming the CNA
and the PIN match, a service order for the SMS can then be
created which matches the user to the physical location -
i.e., matches the CNA to the NNA. At the SMS, this
involves deleting the user from an old physical location (if
previously assigned) and reinstating him or her at the new
location.
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The portability concept can be extended to the
point of full automation where the user interacts with an
interactive Voice Response System which extracts the NNA
from the CLID and the CNA from the user via a telephone dial
pad, then feeds the data to the SMS. This allows users even
more freedom - for example, to temporarily transfer their
service to guest offices and conference rooms. This is
accomplished by marking the NNAs for such locations as being
targets for temporary service only. Service reverts back to
the user's normal location at the end of an interval
established during session setup, or at the end of the
business day.
In general, the concept of identifying users
instead of physical stations allows important network
capabilities to be ported. The assignment of user
privileges is a case in point. With the prior art, user
privileges are assigned to stations at the serving switch.
With the present invention, user privileges are looked up in
the database at the time of CLID lookup and fed to the
Centrex switch where they are inserted into the call data as
a traveling class mark. Thus, privileged users can use
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CA 02224023 1997-12-OS
expensive call routing arrangements, access exclusive
service features, and even be able to barge into calls
within their customer group.
Changes and modifications to the embodiments
described above will no doubt become apparent to those
skilled in the art. The scope of this invention is
therefore intended to be limited solely by the scope of the
appended claims.
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