Note: Descriptions are shown in the official language in which they were submitted.
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ALTERNATE DESTINATION CALL PcEDIRECTION
FOR TELECOMMUNICATIONS SYSTEMS
Technical Field
This invendon relates to arrangements for redirecdng
S telecommunicadons calls when a primary deseinatdon is unavailable or inaccessible.
Problem
. .
A large total volume of telecomrnunications traffic is direc~ed to large
business customers who have geographically diverse facilities for handling the sarne
general type of call. For example, an airline may have privaee branch exchanges
10 (PBXs) for accepting ~eservadons in a number of cides. In such situadons, it is
economically important for the business customer to be aUe to use eheæ facilidesefficiently by ensuring that customers may reach alternate facilides even if a
pardcular preferred PBX facility is unavailable through being busy or because ofcongestdon in the telecornmunicadons network between the caller and the preferred
15 facility. The term PBX as used herein includes automatic call distributor (ACD)
aIrangements controlled at the customer's premises or at a local switch coMectedthereto, and includes central of fice controlled arrangements such as Centrex. The
PBX may be accessed directly from a toll switch or may be accessed via a local
switch.
In one presendy available arrangement, a database is accessed in order
to decide which PBX facility of a pardcular business customer is to receiYe a
pardcular call. This database allocates calls on a percentage basis to the different
automatic call distributors. A disadvantage of this arrangement is that the different
facilides may experience different holding dmes for their calls at any pardcular dme
25 so that even if a fair allocation of the traffic is made, some of these facilides may be
temporarily overloaded and others temporarily underloaded.
In another arrangement, the database maintains a record of the nurnber
of acdve calls which have been directed to each of the automatic call distributors. If
the primary choice PBX for any par~cular call is overloaded, then the call is routed
30 to an alternate PBX. ln this aIrangement, ~he database maintains a ~ecord of the
amount of traffic routed to each PBX in order to detect overloads. Customers can be
automatically routed to other teams of agents if no agents are available at the
preferred PBX but if the other tearns are also busy, the call is queued at the preferred
PBX.
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In another arrangement, if a particular PBX is overloaded it will still
accept the call but reroute it via dedicated private facilities to an alternate PBX.
All of these schemes have a number of limitations. A problem with any
arrangement wherein a database maintains a record of calls to the various ACDs is
5 that congesdon in the toll network or failure in the toll network cannot be readily
detected so and calls continue to be routed to a PBX even though these calls arelikely to be blocked as a result of the network congestion. F~her, the database
maintains a fixed maximum number of calls that can be accepted by each PBX,
although this number is changeable by a traffic adn~inistration; if the PBX is
10 connected to the toll network by facilides shared with other kinds of traffic, for
example, outgoing traffic, this number, in fact, changes dynamically. The
arrangement wherein calls are redirected over private facilides to an alternate PBX is -
costly since all or part of these private facilides are usually provided only for this
purpose; furthermore, the total number of call completions is limited by the access
15 facilities of the primary PBX.
Accordingly, a problem of the prior art is that there is no economically
sadsfactory soludon to the problem of distributing traffic among a plurality of PBX
facilides of a muldlocation or multi-entdty customer which is both capable of roudng
traffic to any PBX having an available server or a sufficiently small queue for such a
20 server, and capable of responding immediately to network congestion or failure
conditions, or customer premises disrupdons, or traffic surges which exceed the
capabilities of a shared access arrangement to serve offered traffic.
Solution
-
In accordance with the principles of this invendon, an advance is made
25 over the prior art in a method and apparatus arrangement wherein calls are inidally
directe~ to a preferred choice destination and, if ~he call cannot be completed
satisfactorily to that destinadon for any reason, the call is redirected to a prespecified
alternate destinatdon. Among the reasons why the call may not be completed are~
congesdon in the toll network required to access the preferred choice or other
30 desdnadons; unavailability of access facilides between the toll network and the
destinatdon; and failure of the toll egress switch for accessing the destination. For
the special case of customers having PBX facilides capable of sending message
signals to the toll network, these reasons are further expanded to include a busy
message from the desdnation or a message from the PBX requesting redirection
35 because of internal overload or any other reason. Advantageously, such an
a~Tangement permits the toll network to allocate traffic dynamically in response to all ~-~
~ s~
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of the above-named conditions.
The desdnation may be a PBX, a central of fice controlled ACD, a
multi-line hunting group or a single line.
In one specific implementation, this kind of messaging capability is
S provided through the facilities of an Integrated Services Digital Network (ISDN)
capability between the switch serving the PBX and the PBX.
In accordance with one feature of this invendon in one specific
embodiment of the invention, one or more databases shared by a toll network
provides an identificatdon of the preferred choice PBX. This identificadon is
10 no~nally in the form of a switch idendficadon, trunk group identification, and a
specific identificadon of the customer premises equipment. In accordance with one
specific implementadon, this number is transmitted to an ingress toll switch in the
form of a non-existent switch number that is used for accessing a translation table
which provides both the idendficadon of the real switch and the trunk number for15 accessing the preferred destinadon PBX. Advantageously, a non-existent switchnumber is a convenient signal that the features of this invention are being invoked
for this call.
In accordance with one aspect of the invention, a customer PBX
responds to an incorning call request by either accepting the call request or rejec~ng
20 it with a call reject message. This call reject message or a corresponding message
triggered thereby is subsequendy transported back to the ingress toll switch and used
as an indicadon to redirect the call. Advantageously, the intelligence of the customer
prernises equipment can be used to make an immediate decision based on current
traffic at that PBX and current availability of agents at that PBX to determine
25 whether to accept the call or to cause the call to be rerouted to another PBX. In
accordance with one aspect of this feature, the PBX may send a call redirecdon
message redirecting the call to a voice message operations center for storing a voice
message ~om the caller. This feature can also be used in the following way. Calls
to different telephone numbers may for the purposes of administration be routed in
~, 30 the same way to the same groups of PBXs. However, these calls may represent
different priority types of business, for example, they may represent complaints or
new orders. Clearly, new order traffic is more important to the business customer
than complaint traffic; the PBX may therefore set a different threshold for rejecdng
complaint calls than for rejecting new order calls. This can be done by sending out a
35 redirect message for a high priority call and a reJect message for a low pnority call.
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The call redirection discussed herein is for redirecting calls at or prior to
the time that the PBX receives an incoming call message. In response to the
incoming call message, the PBX accepts the call either by placing it in a queue or by
immediately connecting it to an agent or rejects the call with or without a request
S that the call be redirected to an alternate PBX.
In another application of this feature, the alternate destination and the
first choice destination are the same. However, the alternate destination is accessed
using a different path through the toll network and preferably using a different egress
toll switch. The two paths and toll egress switches are selected as a result of different
10 translations at the database and toll ingress switch. Advantageously, with such an
arrangement, calls can be completed to a particular PB~ even if the primary egress
switch for serving tha~ PBX is out of service.
In accordance with one aspect of the invention there is provided a
method for routing a call through a public switched network, comprising a plurality of
15 switching systems interconnected in said network, to one of a plurality of destinations,
comprising: responsive to receiving said call in an ingress switching system of said
public switched network, querying a data base shared by a plurality of switchingsystems Oe said network to obtain a routing indication; responsive to receiving a
routing indication from said data base, extending said call via another switching
20 system of said network and via an egress switching system of said network toward one
of said destinations; after extending said call to said another switching system and in ~ `
the absence of receipt of an answer indication on said call, determining in saidanother switching system whether said call can be further extended toward said one
destination; responsive to a determination that said call can be so extended,further
25 extending said call toward said one destination; responsive to a deterrnination that
; said call cannot be so extended, generating and transmitting from said another ~ ~ -
switching system to said ingress switching system a message comprising an indication
that said call cannot be completed to said one destination; and responsive to receiving
said message in said ingress switching system, accessing, in said ingress switching
30 system, alternative routing data related to said routing indication for extending said
call from said ingress switching system toward another of said destinations. ~ -
2023 1 40
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- 4a -
In accordance with another aspect of the invention there is provided in
an interexchange carrier network comprising a plurality of switching systems,
apparatus for routing a call destined for one of a plurality of destinations, comprising:
an ingress switching system, comprising processor means responsive, under program
control, to an incoming call destined for one of said plurality of destinations for
querying a data base shared by a plurality of said switching systems of said network to
obtain routing data for said call; said processor means responsive under programcontrol to receipt of said routing data for extending said call toward one of said
destinations over said network via at leat one other switching system of said network;
and said processor means further responsive, under program control, to a call control
message &om one of said at least one other switching system of said network and in
the absence of receipt of an answer indication for said call, said control message
indicating that said call cannot be competed to said one of said destinations and
supplying an identification of an alternate destination, for extending said call to said
alternate destination.
Brief Description ofthe Drawing
FIG. 1 is a block diagram illustrating how calls are directed and
redirected in accordance with the principles of this invention; and
FIGS. 2 and 3 are flow diagrams of a method for performing redirection
of calls.
Detailed Description
.
FIG. 1 is a block diagram of an example network illustrating how cails
may be redirected in accordance with the principles of this invention. A caller station ~
10 originates a call which can be served from PBX 30 or PBX 39, both associated ;~; `
with the same business. P~3X 30 and PBX 39 might be, for example, two PBXs for ~ -
, serving reservation requests for one airline. PBX 30 and PBX 39 are in different
cities and are served by different switches of a toll network 20. The caller station
accesses toll network 20 via local exchange network 12 which is connected to switch 1
of toll network 20. For the purposes of this call, switch 1 is an ingress switch to the
toll network and switches 2 and 3 connected respectively to PBXs 30 and 39 are ~ i~
egress switches of the network. While only three switches of the network are shown, i`
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20231 40
- 4b -
a typical real toll network may contain many more switches and the connections
between ingress switch 1 and egress switch 2 or egress switch 3 maybe via one ormore intermediate toll switches. In addition, toll network 20 includes a database 4
which is used for obtaining data about certain classes of dialed destinations.
S In this specific example, the telephone number dialed to be connected to
an agent of the airline is an 800 number using the initial digits 800 instead of a
conventional numbering plan area (NPA) code. Calls to 800 numbers are not
i
~ 2~23l~n
restricted to the area served by any one NPA. The principles of routing 800 calls
under the control of a database are disclosed in R. P. Weber, U.S. Patent 4,191,860.
All the toll switches are operative under the control of processor means controlled by
a program. Processor 40, including memory 41 which stores among other items a
5 program 42, is the processor means for controlling ingress switch 1. Egress
switches 2 and 3 have similar processors. When ingress switch 1 receives a call
destined for the airline served by PBX 30 or P3X 39, it first accesses database 4 to
obtain the data necessary to route the call to its destination. Ingress switch 1accesses database 4 via data link 5 with the 800 number dialed from caller station 10.
10 Database 4 responds over data link 5 with a ten-digit number comprising a switch
identification (SSS), a trunk group identification within the switch (TrI) and afurther specific identification of the destination (XXX). In accordance with thespecific embodiment of the invention, for a customer who wishes that calls whichcannot be completed to a prefelred one of that customer's PBXs be redirected to a
15 second of that customer's PBXs, this information from the database contains anumber of a non-existent switch instead of the conventional SSS switch number. In
this case SSS-~ = 208-000. When ingress switch 1 detects that the data returned
by the database includes the number of a non-existent switch, processor 40 of ingress
switch 1 access table 46 using the returned non-existent switch number and the
20 returned TIT number to obtain the real number of the switch which is connected to
the preferred choice PBX, in this case, PBX 30. The transladon therefore is from the
non-existent switch number to the number 002 which identifies egress switch 2
connected to the preferred PBX 30. Ingress switch 1 sends an initial address
message 50 comprising the non-existent switch number as well as the TTI and
25 XX~ number 51 obtained from the database 4 and routes the call toward egress
switch 2, the switch identified in the translation of table 46. The call is routed to
egress switch 2 which translates the incoming address message in its own version of ;
table 46 and discovers that the identification of the switch for SSS-Tl'r equals 208
000 is itx own switch number. Switch 2 obtains in its own translation table the
30 number of the trunk group 178 to be used for accessing the desired destination, in
this case PBX 30.
: - -
If the call has not been successfully extended to egress switch 2, a
release message for the Gall is sent from the point at which the extension was not
successfuL lf egress switch 2 detects an all circuits busy connection for circuits to
35 PBX 30, egress switch 2 will send a release message. If PBX 30 is a program
controlled system comprising a processo~ 31 and message generating capabilities, : -
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-- 2~231~
and wishes to reject the call, it will send a call rejection message 58 comprising a
reason for rejection segment 59 back to egress switch 2. In response to receiving
such a rejection message, egress switch 2 will send back to ingress switch 1 a release
message 60 comprising a reason for release indicator 62. If release messages have
S been generated for any of the reasons discussed above and transmitted to ingress
switch 1, whatever portion of the connection ~From ingress switch 1 toward PBX 30
has been established, is released and ingress switch 1 consults table 44 to determine
an alternate non-existent switch code corresponding to switch code 208, In this case
the alternate non-existent switch code is 209. The entry in table 46 of processor 40
10 of ingress switch 1 corresponding to 209-000 (000 is the lTI number originally
provided by database 4) is 3. Therefore, a second initial address message 65
containing the number 209-000 (segrnent 66) is transmitted to egress switch 3,
switch 3 having been the switch identified in the above-noted access of table 46.
Switch 3 translates 209-000 to 3-195, thus discovering that the call is destined for
itself, trunk group 195. Thereafter, if PBX 39 is able to accept the call, the call is -
extended from ingress switch 1 via egress switch 3 to PBX 39.
The specific reason for the release may be used to modify the
redirection. For example, if the redirecdon is to the same desdnatdon via another
egress switch, no redirection is performed if the reason is that the called subscriber is
20 busy.
In this specific embodiment, table 44 is used to advance from one non-
existent switch number to the next. Alternadvely, a programmed algorithm for
performing this advance (such as incremendng by 1 but limited to some specified
parameter, such as 212 to be comparable to the table 44 prescription) could also be
25 used. If, in a pardcular situadon, the number of alternate PBX desdnadons is fini~e
then the attempt to advance beyond the last alternate PBX is signaled by having a
translation in table 46 which indicates a non-existent switch number as a signal that
there are no ~e PBXs to which calls can be redirected. Further, while in this
example the egress switch is directly connected to the PBX, it can be connected to
30 the PBX via a local exchange network provided that the local exchange network has
a satisfactory method of signaling to the egress switch tha~ the call cannot be
satisfactorily completed to the selected destination. Note that the desdnation need
not be a PBX, but could be a single line customer, or any other destination.
There are, of course, many other alternative data layouts which can be
35 used to accomplish the fundamental obiectives of allowing for the recognition of a
call which may be redirected from one destination to another; allowing for the
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2~231 ~
- 7 -
termination of attempts to redirect the call; providing an indication to a selected
egress switch that the call is to be connected to a destination connected to that egress
switch, and identifying the proper trunk group for accessing the PBX. For exarnple,
table 46 can be a~ranged to supply the primaly and alternate switch numbers and to
5 use the table 44 to advance from one non-existent switch number to the next or to
provide the primary switch number and an alternate non-existent switch number and
I~T number which latter could then be used for accessing table 46 to find the next
alternative switch and next alternative non-existent switch number and TTT number.
Further, a separate table could be used for identifying 1~ numbers associated with
10 a switch acting as an egress switch.
FIG. 2 is a flow diagram of actions performed to irnplement automatic
redirecdon in accordance with the prin~iples of this invention. The flow diagramillustrates a specific example of a call but it will be apparent from the example what
actions are performed by the program in a general case.
15Suppose that the caller dials an 800 number, in this case
1-800-234-5678 (action block 202) The caller is connected via local exchange
network 12 to switch 1. Switch 1 requests routing from database 4 for the callednumber 1-800-234-5678 (action block 204). Database 4 returns to ingress switch 1 a
number OI the format SSS~TI XXXX wherein SSS specifies a switch number, l~IT a
20 trunk group within that switch, and XX~ a specific identificadon of the called
destinadon. In this case, database 4 retums the number 208-000-1234 (acdon
block 206). 208 is an identificadon of a non-existent switch (the AT&T network ;
contains fewer than 150 toll switches). The number 208-000 is used by ingress -
switch 1 to access memory table 46 which has a record corresponding to the 208-000
25 accessing number that indicates that the preferred desdnadon egress switch isswitch 2 (acdon block 207). Switch 1 then sends an inidal address message with the
desdnation field containing the number 208-000-1234 and routes the call to egress ~;
switch 2 (action block 210). Egress switch 2 is the switch whose number was
obtained in the transladon step 207. Test 212 checks whether the call encounters30 network congestion. If so, a release message is sent from the point of congesdon to
switch 1 (action block 214). Note that in case switch 1 itself detects that congestion
will be encountered in trying to access switch 2, that the acdons beginning withaction block 240, described hereinafter, are immediately initiated. If test 212
indicates that the call has not encountered network congestion, test 216 (FIG. 3)
35 checks whether the call encounters an all circuits busy condition at the destination
PBX 30. If so, then a release message is sent to switch 1 from egress switch 2
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- 8 -
(action block 214, FIG. 2). If the result of test 216 (FI(3. 3) is negative then PBX 30
tests whether it wants to reject the call. Outright call rejection as opposed toredirection might be requested if the PBX is overloaded, if the call is low priority,
and if there are indications that alternate PBX's are also overloaded. If so, then the
5 PBX sends a reject message to switch 2 (action block 220) and switch 2 generates a
release message with reason indicator 62 set to reject (action block 221) and sends
this message to switch 1 (acdon block 214). If the result of test 218 is negative, then
test 222 is used to test whether the PBX wants to redirect the call. This may occur
because too many calls are in the queue for the number of active agents; the
10 incoming queue has no more space; there has been an unexpected work stoppage; or
only pnority type calls, such as calls to place orders, can be accepted at this PBX. If
the PBX wants to redirect the call, then the PBX sends a redirect indication to
switch 2 (action block 224) and switch 2 converts the redirect indication into arelease message (action block 226), in this case, with the reason indicator 62 being
15 marked redirect. The release message is then sent to switch 1 (action block 214,
FIG. 2). If the PBX does not want to redirect the call, then the PBX will accept the
call and the call is completed (action block 228, FIG. 3).
Following the sending of a release message to switch 1 (action
block 214, FIG. 2), described above, switch 1 receives the release message (acdon
20 block 23û). Switch 1 then performs test 232 to determ~ne whether or not the release
message is for a redirectable call. In applicants' specific embodiment, the same type
of release message is used for simple release in case of busy as for a requestedredirecdon; this has reduced the development effort required to implement
applicants' invendon. Other reasons why the release message might not be for a
25 redirectable call are that the customer has not subscribed to call redirection service,
or that the redirecdon is only acdve during certain hours of certain days of the week,
or that only calls originating in certain NPA codes should be redirected. If therelease message is not for a redirectable call, then the call is released under the
control of ingress switch 1 (action block 234). If the release message is for a
30 redirectable call (positive result of test 232) then ingress switch 1 translates from the
non-existent switch number associated with this call attempt (in this case 208) to find
the redirect alternative non-existent switch number (action block 240). (The redirect
alternative non-existent switch number for 208 is 209 as specified in table 44).Ingress switch 1 then uses the new non-existent switch number to access table 4635 using the same lTI number (000) originalIy provided by database 4 to obtain the
identification of an egress switch for the alternative destination PBX. In this case,
' ` ; ~ I !
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2023141)
g
table 46 indicates that the egress switch number corresponding to SSS-l~IT =
209-000 is switch 3, the switch connected to PBX 39 which is the alternative
destination PBX. Ingress switch 1 then sends an IAM message with
destinadon 2û9-000-1234 routing the call to switch 3 identified in action block 242
5 (action block 244). Thereafter, the same actions previously described for blocks 212
starting with block 212 are performed except in this case switch 3 will send therelease message to switch 1.
The basic principles discussed above can be used to redirect a call more
than once if the first redirected to destination is also unavailable.
While in this specific embodiment, the database supplies only an initial
translation and the subsequent translations are made in the ingress switch, it is also
possible to perform all the translations in the database by providing a list of
alternative destinations to ingress switch 1 at the time of the first access or to request
the alternative destinations in a series of subsequent queries. The advantage of15 providing these translations from the database is that only one database need be
updated as customers for whom redirect capabilities are added or as customers
change their redirection requests.
Alternatively, the PBX could provide the redirection number as part of
the message and thus retain control of the redirection process.
In other arrangements for other types of calls, the routing data can be
directly stored in ingress switch 1, thus avoiding the necessity for accessing remote
database 4. For example, for a particularly important destination, such as a ~
government bureau, for added security, the alternative destinations may be stored ~`
directly in ingress switch 1. Also for destinations serving very high volume traffic, it
25 is desirable to avoid the extra per call database access by storing the routing da~a in
ingress switch 1.
The call may originally be routed to a local exchange controlled Centrex -
which is programmed to give the same kinds of response messages discussed above -
for a program controlled PBX. - .-
It is to be understood that the above description is only of one prefeIred
embodiment of the invendon. Numerous other arrangements may be devised by one ;
skilled in the art wi~out departing from the spirit and scope of the inven~on. The
invention is dlus li}mLted only as defined in the accompanying claims.
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