Telephonic communications – Plural exchange network or interconnection – With interexchange network routing
Reexamination Certificate
1997-12-22
2001-12-18
Hong, Harry S. (Department: 2642)
Telephonic communications
Plural exchange network or interconnection
With interexchange network routing
C379S201010, C379S221030, C379S221010
Reexamination Certificate
active
06332022
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The invention relates to a method and apparatus for handling of calls for emergency services in telecommunications networks and, in particular, so-called intelligent networks.
The invention is also applicable to routing within an intelligent network of emergency services calls from mobile stations.
2. Background Art
In existing telecommunications networks, particularly in North America, telephone calls for emergency services are routed to a Public Service Access Point (PSAP) which is staffed by emergency services operators and, for reasons of reliability and continuity of service, is accessed by way of a tandem switch dedicated to such emergency services. To access emergency services, the caller dials the emergency services access code, which in North America is 9-1-1. When the end office detects the digits 9-1-1, instead of routing the call like a normal voice call, it routes the call immediately to the 9-1-1 tandem switch which routes the call to the Public Service Access Point. In order to determine the most appropriate emergency services centre to provide the required services, the emergency services operator will determine the location of the caller by first obtaining the calling line identifier, either automatically if the tandem switch is provisioned with Automatic Number Identification (ANI), or by questioning the caller, and using it to access an Automatic Location Identification database (ALI) and obtain the geographical location of the caller.
Although it is usual to provide a second ALI database as a “hot spare” to ensure reliability of service, this existing way of handling emergency services calls is not entirely satisfactory because, if the trunks between the end office and the dedicated tandem switch, or between the tandem switch and the PSAP, were blocked, that PSAP could not supply the necessary emergency service to that caller. A further disadvantage is that automatic location identification is not available for mobile users.
An object of the present invention is to overcome or at least mitigate these deficiencies of existing emergency services systems. To this end, the present invention provides for calls for emergency services to be alternate routed using out-of-band or common channel signalling.
SUMMARY OF THE INVENTION
According to one aspect of the present invention, there is provided a method of handling emergency services calls from calling parties in an intelligent network having a plurality of emergency services operator stations, at least one Service Control Point (SCP) equipped with software for providing service features and having access to databases including routing data for said plurality of emergency services operator stations, a plurality of Service Switching Points (SSP) equipped with call processing software having point-in-call triggers for interrupting processing of a call and exchanging signalling messages with the Control Point (SCP) to obtain instructions for further processing of the call, and the Service Switching Points and Service Control Point (SCP) being interconnected by an out-of-band signalling system, the Service Switching Points being interconnected by trunks for calls therebetween, and the plurality of emergency services operator stations being each connected by trunks or lines to at least one of said Service Switching Points, the said routing data comprising routing numbers each identifying a network location for a respective one of said plurality of emergency services operator stations the routing data associating with each calling party a primary emergency services operator station and at least one alternative emergency services operator station, the method comprising the steps of:
(i) at a particular Service Switching Point, presetting a point-in-call trigger to operate at a predetermined point in a call for emergency services,
(ii) subsequently, when said particular Service Switching Point is processing an emergency services call, interrupting processing of the call and transmitting to the Service Control Point (SCP) a query signalling message requesting routing information,
(iii) at the Service Control Point (SCP), upon receipt of the query signalling message, accessing said routing data in dependence upon parameters in the query signalling message and selecting a routing number corresponding to said alternative emergency services operator station for that calling party, forming a response signalling message including the selected routing number and returning such response signalling message to said particular Service Switching Point,
(iv) at said particular Service Switching Point, upon receipt of said response signalling message, detecting the selected routing number, and routing the call to the network location corresponding to the selected routing number for completion to said alternative emergency services operator station.
The method may include the prior steps, at the Service Switching Point, of attempting to complete the emergency services call to a primary emergency services operator station on the basis of the dialled digits received from the calling party, and detecting that the call did not complete, the point-in-call trigger being selected to operate following failure of such initial call completion attempt.
Alternatively, the point-in-call trigger may be set to interrupt processing of all calls to emergency services operator stations upon receipt of the dialled digits from the calling party.
According to a second aspect of the present invention, there is provided apparatus for handling emergency services calls from calling parties in a telecommunications network employing an SS7 signalling system, the apparatus comprising a plurality of emergency services operator stations, at least one Service Control Point (SCP) equipped with software for providing service features and databases including routing data for said plurality of emergency services operator stations, a plurality of Service Switching Points equipped with call processing software having point-in-call triggers for interrupting processing of a call and exchanging signalling messages with the Service Control Point (SCP) to obtain instructions for further processing of the call, the Service Switching Points and Service Control Point (SCP) being interconnected by said SS7 signalling system, the Service Switching Points being interconnected by trunks for calls therebetween, and each emergency services station being connected trunks to at least one of the Service Switching Points, the routing data comprising routing numbers each identifying a network location for a respective one of the emergency services stations the routing data associating with each calling party a primary emergency services operator station and at least one alternative emergency services operator station, each Service Switching Point comprising:
means for presetting a point-in-call trigger to operate at a predetermined point in the processing of an emergency services call from a calling party, and
means operative during processing of a subsequent call for emergency services to interrupt processing of the call and transmit to the Service Control (SCP) Point a query signalling message requesting routing information, each Service Control Point (SCP) comprising:
means operative, upon receipt of the query signalling message, for accessing the routing data in dependence upon parameters in the query signalling message and selecting a routing number for said alternative emergency services station for that calling party, forming a response signalling message including the selected routing number and returning such response signalling message to the requesting Service Switching Point, each Service Switching Point further comprising means operative, upon receipt of said response signalling message, for routing the call to the network location corresponding to the selected routing number for completion to said alternative emergency services station.
The Service Switching Point may comprise means operative to attempt to complete the emergency s
Anderson Chad C.
Deane, Jr. William J.
Hong Harry S.
Nortel Networks Limited
Shannon John P.
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