Abstract:
A method is provided for routing an emergency call from Customer Premises Equipment (CPE) to a Public Safety Answering Point (PSAP). The method includes: establishing a session over a packet-switched network ( 200 ) between a CPE ( 110 ) and a network node ( 302 ), such that the CPE ( 110 ) accesses a Public Switched Telephone Network (PSTN) ( 400 ) from the network node ( 302 ) via a telecommunications switch ( 500 ) associated with a first PSAP ( 320 ) serving a geographic region ( 300 ) different than where the CPE ( 110 ) is currently located; identifying a telephone number for a second PSAP ( 120 ) serving the geographic region ( 100 ) in which the CPE ( 110 ) is located; and, substituting the identified telephone number for a dialed telephone number when the dialed telephone number is indicative of an emergency call.

Description:
FIELD 
     The present inventive subject matter relates to the telecommunication arts. Particular application is found in conjunction with public access emergency telecommunication services (e.g., emergency 911 calls) and the specification makes particular reference thereto. However, it is to be appreciated that aspects of the present inventive subject matter are also amenable to other like applications. 
     BACKGROUND 
     With reference to  FIG. 1 , packet switched networks (such as the Internet or a managed private internet  10 ) are being used to route voice telephone calls. Generally, this is known as voice-over-packet telephony, which includes, but is not limited to, VoIP (Voice over Internet Protocol). One of the advantages of voice-over-packet telephony is the ability for remote users to access the Public Switched Telephone Network (PSTN)  20  through their company&#39;s home telecommunication switch. 
     Various types of Customer Premises Equipment (CPE) are available for end users to participate in voice-over-packet telephony, e.g., an IP telephone, which may be a hardphone or a softphone running on a laptop computer or other like platform. For example,  FIG. 1  shows a typical case where a user, in a remote location or geographic region  30  (e.g., Cleveland, Ohio), is using a softphone running on a laptop computer  40  to engage in voice-over-packet telephony. The computer  40  is connected over the Internet  10  back to the user&#39;s home location or geographic region  32  (e.g., Phoenix, Ariz.), e.g., back to the user&#39;s office or normal place of business. Accordingly, access to the PSTN  20  is achieved via the user&#39;s company home switch  50  (e.g., a class 5 switch such as the Lucent Technologies 5ESS or another like switch). 
     The foregoing is a beneficial arrangement since other callers can reach the user by dialing their normal office telephone number. Similarly, calls made by the remote user appear to come from the user&#39;s normal office telephone number, e.g., such that the normal office telephone number is displayed on the called party&#39;s caller-ID, if available. The user may also be able to utilize PBX (Private Branch eXchange) and/or Centrex features supported at their home office or home switch  50 . This arrangement, however, can present certain problems for handling emergency calls, such as 911 calls. 
     As is known in the art, the PSTN  20  includes mechanisms for directing certain calls, such as an emergency 911 call, to a Public Safety Answering Point (PSAP). Commonly, different PSAPs serve different geographic regions. PSAP  60 , for example, serves region  30 , while PSAP  62 , serves region  32 . Accordingly, when a PSAP receives a 911 call, the corresponding regional safety officials or first responders (e.g., fire department, police, ambulance, etc.) can be called or mobilized as deemed appropriate for the circumstances. It is, therefore, desirable that 911 calls get routed to the PSAP serving the geographic region in which the calling party is currently located so that a proper response to the 911 call can be quickly and readily coordinated. 
     In the example shown in  FIG. 1 , if the remote user located in region  30  were to make a 911 call, it would appear to the PSTN  20  that the 911 call was originating from region  32  insomuch as the PSTN  20  was being access via the user&#39;s company home switch  50 . Absent suitable provisioning otherwise, the 911 call would be undesirably routed to the PSAP  62  serving the region  32 , rather than to the PSAP  60  serving the region  30  where the user is currently located. 
     Accordingly, a new and improved system and/or method for handling voice-over-packet emergency calls is disclosed that overcomes the above-referenced problems and others. 
     SUMMARY 
     In accordance with one embodiment, a method is provided for routing an emergency call from Customer Premises Equipment (CPE) to a Public Safety Answering Point (PSAP). The method includes: establishing a session over a packet-switched network between a CPE and a network node, such that the CPE accesses a Public Switched Telephone Network (PSTN) from the network node via a telecommunications switch associated with a first PSAP serving a geographic region different than where the CPE is currently located; identifying a telephone number for a second PSAP serving the geographic region in which the CPE is located; and, substituting the identified telephone number for a dialed telephone number when the dialed telephone number is indicative of an emergency call. 
     In accordance with another aspect, a system is provided for routing an emergency call from Customer Premises Equipment (CPE) to a Public Safety Answering Point (PSAP). The system includes: means for establishing a session over a packet-switched network between a CPE and a network node, such that the CPE accesses a Public Switch Telephone Network (PSTN) from the network node via a telecommunications switch associated with a first PSAP serving a geographic region different than where the CPE is currently located; means for identifying a telephone number for a second PSAP serving the geographic region in which the CPE is located; and, means for substituting the identified telephone number for a dialed telephone number when the dialed telephone number is indicative of an emergency call. 
     Numerous advantages and benefits of the inventive subject matter disclosed herein will become apparent to those of ordinary skill in the art upon reading and understanding the present specification. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present inventive subject matter may take form in various components and arrangements of components, and in various steps and arrangements of steps. The drawings are only for purposes of illustrating example embodiments and are not to be construed as limiting. Further, it is to be appreciated that the drawings are not to scale. 
         FIG. 1  is a block diagram illustrating an example of a conventional telecommunications network for handling 911 calls. 
         FIG. 2  is a block diagram illustrating an exemplary telecommunications network suitable for practicing aspects of the present inventive subject matter. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     For clarity and simplicity, the present specification shall refer to structural and/or functional elements, entities and/or facilities, relevant communication standards, protocols and/or services, and other components and features that are commonly known in the telecommunications art without further detailed explanation as to their configuration or operation except to the extent they have been modified or altered in accordance with and/or to accommodate the embodiment(s) presented herein. 
     With reference to  FIG. 2 , a user is located in a first geographic region  100 , and uses customer premises equipment (CPE)  110  to selectively place telephone calls. The CPE  110 , as illustrated, is an IP telephone, suitably, a hardphone or a softphone running as an application on a general purpose computer, laptop computer or other suitable platform. However, the CPE  110  may be any traditional packet-based CPE, e.g., used to engage in VoIP, voice-over-packet, facsimile, data or other like calls. In the usual manner, the CPE  110  operatively connects with a packet-switched network  200 , such as the Internet or another managed or unmanaged packet-switched network. 
     Suitably, the CPE  110  connects via the packet-switched network  200  to an IP or packet-based entity and/or connection point  302  in a second geographic region  300  that is different from the first geographic region  100 . For example, the second geographic region  300  may include the user&#39;s home region or the user&#39;s home office or normal place of business. Accordingly, the CPE  110  accesses the PSTN  400  from the connection point or node  302  via a telecommunications switch  500  serving the second region  300 . Optionally, the connection point  302  is the following mentioned gateway or softswitch, or alternately, it may be an IP or packet-based Centrex or PBX supported, respectively, by the switch  500  or at the user&#39;s home office or normal place of business. It is to be appreciated that, suitably, the remote location  100  is geographically distinct from the home location  300 , at least insomuch as the remote location  100  is served by a PSAP  120  that is different from a PSAP  320  serving the home location  300 . 
     Suitably, the switch  500  is a class 5 switch such as the Lucent Technologies 5ESS or another like circuit switch. The switch  500  is optionally paired with an appropriate gateway for bridging together circuit-switched and packet-switched networks. The telecommunications switch  500  is operatively connected to the PSTN  400  in the usual manner. The gateway (e.g., an IP gateway) is operatively connected between the switch  500  and the packet-switched network  200  thereby bridging the packet-switched network  200  with the PSTN  400  in the usual manner. That is to say, the gateway acts as a point of entry for packet-switched calls from the network  200  headed into the PSTN  400 , and similarly acts as a point of entry for circuit-switched calls from the PSTN  400  headed into the packet-switched network  200 . In the usual manner, the gateway selectively converts and/or translates packet-switched calls into circuit-switched calls and vice versa depending on the direction of traffic flow. For example, a suitable gateway is an iMerge® gateway provided by Lucent Technologies. Optionally, the combination of the switch and gateway is replaced by a softswitch that acts as the functional equivalent of the combination. 
     Before calls are placed with the CPE  110 , it is first registered with the connection point or entity  302 . At registration, the location of the CPE  110  is determined. That is to say, it is determined if the CPE  110  is connecting from a remote location, such as region  100 . Suitably, upon initialization of the remote CPE  110  (e.g., at the time of connection to the packet-switched network  200 ), a registration message is sent from the CPE  110 , over the packet-switched network  200  to the connection point or entity  302 . The location of the CPE  110  is optionally recognized as remote based upon where it is accessing the connection point  302  from, e.g., the location is deemed remote if the CPE  110  is not accessing the connection point or entity  302  from a known local IP address. If deemed to be accessing remotely, a current location for the remote CPE  110  is then established. 
     To establish the remote location of the CPE  110 , an identifier indicative of the remote location is obtained, e.g., from the registration message or at the time of registration. Suitably, the identifier is a local telephone number associated with the CPE&#39;s current location. For example, if the CPE  110  connects to the packet-switched network via a dial-up connection, through a modern pool or via a remote access server, the local number associated with the CPE&#39;s current location, is optionally obtained by the connection point or entity  302  via caller-ID, an Automatic Number Identification (ANI) spill, or the like. Alternately, the CPE  110  may be connecting, e.g., from a known non-local IP address such as an IP address for a branch office located in the region  100 . In this case, the connection point or entity  302  may optionally be provisioned with particular telephone numbers associated with locations within which particular ranges of IP addresses are used, or they may be obtainable from a suitable database. In yet another embodiment, if the associated local telephone for the CPE&#39;s current location is not automatically detected and/or obtained by one of the two means described previously, a dialog is launched between the CPE  110  and the connection point  302  in which the user may manually enter the local telephone associated with the CPE&#39;s current location. 
     Once the current remote location of the CPE  110 , and hence the remote user, has been established, the telephone number (e.g., a North American Numbering Plan (NANP) telephone number) for the PSAP serving that remote location is obtained or otherwise determined. Suitably, a PSAP database  600  is maintained that is accessible by the connection point or entity  302 . The database  600  contains a look-up table (LUT) or otherwise relates input telephone numbers with telephone numbers for the various PSAPs. That is to say, given a particular input telephone number, the database returns or otherwise provides the telephone number for the PSAP serving the geographic region corresponding to the given input telephone number. Suitably, the previously obtained local telephone number associated with the CPE&#39;s current remote location is used to query the database  600 . For example, the query may be accomplished by the use of an IP or other packet-switched message, optionally, sent to a PSTN SCP (Service Control Point). Such an arrangement would allow the database  600  to be used directly by IP or packet capable agents, as well as SS7 (Signaling System 7) based switches within the PSTN  400 . 
     Once the appropriate PSAP telephone number is identified and/or obtained, it is substituted as the dialed telephone number should a 911 call be placed from the remotely located CPE  110 . In one embodiment, for example, the identified PSAP telephone number is forwarded to the CPE  110  during the registration process. The CPE  110  is accordingly programmed and/or provisioned to store the received PSAP telephone for the duration of the session and substitute it as the dialed telephone number should a user dial 911 on the CPE  110 . Alternately, the substitution is made by and/or takes place at the connection point or entity  302 . For example, a Emergency Call Telephone Number Substitution (ECTNS) database  610  is optionally maintained. Suitably, the database  610  contains a list of registered remote CPE along with the respective PSAP telephone number corresponding to the current remote location of each CPE. In either case, when a 911 call is placed from the CPE  110  located in region  100 , the telephone number for the PSAP  120  serving the region  100  is substituted as the dialed number. Recall, that at or about the time of registration of the CPE  110  with the connection point or entity  302 , the telephone number for the PSAP  120  was read or otherwise obtained from the database  600 . 
     Consequently, when 911 (or another recognized emergency call number) is dialed on the remotely located CPE  110 , the telephone number for the PSAP  120  is effectively called and the call is therefore routed over the PSTN  400  or otherwise to the PSAP  120 . As can be appreciated, this is the proper PSAP serving the current location of the CPE  110  and its user. 
     It is to be appreciated that in connection with the particular exemplary embodiments presented herein certain structural and/or function features are described as being incorporated in defined elements and/or components. However, it is contemplated that these features may, to the same or similar benefit, also likewise be incorporated in other elements and/or components where appropriate. It is also to be appreciated that different aspects of the exemplary embodiments may be selectively employed as appropriate to achieve other alternate embodiments suited for desired applications, the other alternate embodiments thereby realizing the respective advantages of the aspects incorporated therein. 
     It is also to be appreciated that particular elements or components described herein may have their functionality suitably implemented via hardware, software, firmware or a combination thereof. Additionally, it is to be appreciated that certain elements described herein as incorporated together may under suitable circumstances be stand-alone elements or otherwise divided. Similarly, a plurality of particular functions described as being carried out by one particular element may be carried out by a plurality of distinct elements acting independently to carry out individual functions, or certain individual functions may be split-up and carried out by a plurality of distinct elements acting in concert. Alternately, some elements or components otherwise described and/or shown herein as distinct from one another may be physically or functionally combined where appropriate. 
     In short, the present specification has been set forth with reference to preferred embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the present specification. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.