Patent Publication Number: US-2016242016-A1

Title: Ss7 ansi-40 to sip based call signaling conversion gateway for wireless voip e911

Description:
The present application is a continuation application of U.S. patent application Ser. No. 14/287,561, filed 27 May 2014, which is a continuation of U.S. Patent application Ser. No. 13/532,344, filed 25 Jun. 2012; which is a continuation of U.S. Patent application Ser. No. 11/417,126, filed 4 May 2006 (now U.S. Pat. No. 8,208,461, issued on 26 Jun. 2012); which claims priority from U.S. Provisional Application No. 60/788713, filed 4 Apr. 2006, entitled “SS7 ANSI-41 TO SIP BASED CALL SIGNALING CONVERSION GATEWAY FOR WIRELESS VoIP E911”, to Mitchell, the entirety of which are expressly incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to E9-1-1 emergency phone calls. More particularly, it relates to handling emergency E9-1-1 calls using Voice Over Internet Protocol (VoIP). 
     2. Background of the Related Art 
     Voice Over Internet Protocol (VoIP) is a technology that has been developed as an alternative packet-based telephony technology to the conventional switched telephony service (e.g. PSTN). VoIP takes advantage of high speed Internet data networks, and is able to provide low cost telephony services to end users. VoIP technology emulates a phone call, but instead of using a circuit based switched system such as the telephone network, utilizes packetized data transmission techniques most notably implemented in the Internet. 
     VoIP phone calls are routed to a VoIP voice gateway, from which they are passed on to their destination VoIP device. Conventional VoIP voice gateways (i.e., soft switches) are typically located in only a few places across the country. A soft switch is a programmable network switch that can process the signaling for all types of packet protocols. Also known as a ‘media gateway controller,’ ‘call agent,’ or ‘call server,’ such devices are used by carriers that support converged communications services by integrating signaling system No. 7 (SS7) type switched telephone signaling with packet networks. Softswitches can support, e.g., IP, DSL, ATM and frame relay. 
     Because VoIP is Internet Protocol (IP) based, call related information such as CallerID type services may not be available or accurate. A location of a given VoIP device may be statically provisioned to be at a given geographic location, or queried from a home location register (HLR) in a mobile system. 
     911 is a phone number widely recognized as an emergency phone number that is routed to emergency dispatch personnel and used to determine a location of a caller. Enhanced 911 (E911) is defined by the transmission of callback number and location information to the relevant public safety answering point (PSAP). A PSAP is the endpoint of an emergency services call. PSAPs are responsible for answering emergency services calls. E911 may be implemented for landline and/or mobile devices. Some Public Safety Access Points (PSAPs) are not enhanced, and thus do not receive the callback or location information from any phone, landline or mobile. 
     The problem is not necessarily solved with the use of a centralized emergency call center. In such case, when a VoIP customer places an emergency call such as an E911 call, the call may be routed to an emergency call center that is very far away, and in some instances half-way across the world to reach the centralized emergency call center. The VoIP E911 call must then be transferred to the relevant 911 center (public safety access point (PSAP)). However, this transfer must take place over the Public Switched Telephone Network (PSTN) because such transfer cannot conventionally be gained to the PSAP&#39;s existing Enhanced 911 (E911) dedicated network where location and callback number of the originating 911 caller are provided. Moreover, note that even the call related information (e.g., CallerID) provided with the call would relate to the identity and location of the centralized call center—not to the callback number and certainly not the location of the customer originally dialing 911. 
       FIG. 7A  shows conventional relevant systems in an emergency 911 call made via a wireless caller in a GSM network. 
     In particular, as shown in  FIG. 7A , a wireless GSM caller  190  dials 911. The 911 call is serviced by a cell site of a service provider, which includes a given mobile servicing center (MSC)  402 . The MSC  402  performs a query of a PSAP Automatic Location Identification (ALI) database  406  via a gateway mobile location centre (GMLC)  432  to determine a unique 10-digit phone number of the proper local PSAP physically responsible for the location of the 911 caller  190 . 
       FIG. 7B  shows conventional relevant systems in an emergency 911 call made via a wireless caller in a CDMA or TDMA network. 
     In particular, as shown in  FIG. 7B , a wireless CDMA or TDMA caller  190   b  dials 911. The 911 call is serviced by a cell site of a service provider, which includes a given mobile servicing center (MSC)  402 . The MSC  402  performs a query of a PSAP Automatic Location Identification (ALI) database  406  via a mobile positioning center (MPC)  707  to determine a unique 10-digit phone number of the proper local PSAP physically responsible for the location of the 911 caller  190   b.    
     As technology progresses, dual mode wireless phones have emerged. A dual mode wireless phone is one that operates using CDMA or GSM technology when out on the open road, but which switches to a local area network such as a Wireless Fidelity (WiFi) network when within range at home or in the office. For instance, a wireless phone may join a WiFi network created in a home or office used by a wireless computer network, when within range of that WiFi network, to gain access to the Internet and thus communicate using voice over Internet Protocol (VoIP). Thus, dual mode phones operate as an ordinary cell phone as a mobile user traverses a cell network (e.g., a CDMA network), until you get home or to your office containing a WiFi network, at which time the cell phone drops use of the CDMA network and instead switches over to use of the WiFi network. 
     When a wireless phone is mobile and away from home or the office, latitude/longitude location information is pretty much the best that can be provided. However, when within a home or office on a WiFi network, it is preferable that more accurate location information such as MSAG format location information including street address be provided instead of merely lat/lon type location information. 
     Unfortunately, provision of MSAG format location information along with a WiFi wireless call presents significant expense to a wireless carrier. Instead, without change to the wireless carrier&#39;s network, lat/lon location information is the best that can be provided in all cases, even when the wireless dual mode phone is communicating over the Internet using a WiFi network. 
       FIG. 8  shows one conventional solution to delivery of location data in wireless E911 format, but providing only latitude/longitude (lat/lon) location information. 
     In particular, as shown in  FIG. 8 , a wireless caller  190  using a dual mode phone dials 911. 
     A user agent  180  provides service to the wireless VoIP device  190  so that the dual mode phone is provided with wireless Internet access. (“User agent” is a common name for a device that makes a VoIP call, e.g., a SIP phone, Skype™ on a Personal Computer, etc.). 
     The call then progresses over the Internet (Voice Over Internet Protocol (VoIP)) via a wireless fidelity (WiFi) access point  170 . A WiFi access point  170  is, e.g., a wireless local area network hub in a house or office. The WiFi access point  170  provides Internet access to the wireless dual mode phone  190  typically via a wired connection to the Internet. (While described with respect to WiFi, the invention as described below relates equally to later embodiments of local area network hot spots (e.g., WiMAX, etc.). 
     A wireless VoIP base station controller  160  communicates with the WiFi access point  170  to provide circuit switched, time-division multiplexing (TDM) access to the VoIP call. 
     The user agent  180 , WiFi access point  170  and a Wireless VoIP base station controller  160  use TCP/IP transport and session initiation protocol (SIP) protocols. 
     From the wireless VoIP base station controller  160 , the VoIP E911 call is passed to a mobile switching center (MSC)  800 . If part of a CDMA network, the MSC  800  passes an Origination Request (ORREQ) message (IS-41) to a 3 rd  Generation Partnership (3GPP2) mobile positioning center (MPC)  802  per the 3GPP2 joint standard #36 (J-STD-036). The ORREQ starts the process where location is ultimately obtained from a Position Determination Entity (PDE). The PDE consumes, or uses, the location information itself. 
     If part of a GSM network, the MSC  800  passes a subscriber location report (SLR) request to a Gateway Mobile Location Center (GMLC)  802 . An SLR is a push of location. Thus, location is actually obtained before the message is sent. In such a GSM network, the MSC  800  actually gets the location back from the network element (SMLC) on the time division multiplex (TDM) side. The MSC  800  then provides the location to the GMLC  802 . 
     The VoIP E911 call is then directed to a selective router  140  serving the designated public safety access point (PSAP)/911 network  195  for the determined lat/lon location. 
       FIG. 9  shows a conventional delivery of location data in MSAG format for VoIP calls for processing E911 calls using the NENA approved i2 call flow. 
     In particular, as shown in  FIG. 9 , a dual mode phone user  190  makes a 911 call over their WiFi network as otherwise described in  FIG. 8 . For instance, the VoIP E911 call is serviced by a user agent  180 , a WiFi access point  170 , and a wireless VoIP base station controller  160 , as otherwise shown and described with respect to  FIG. 8 . However, in the embodiment of  FIG. 9 , the wireless carrier is a voice service provider network  900 , enjoying the benefits of a VoIP network. 
     The voice service provider network  900  passes a SIP invite message to a VoIP positioning center  904 . The SIP invite is used to get location information from the VPC  904 . In this scenario, location is determined by the VPC  904 , and the VPC  904  is used to make decisions based on that location. In particular, the VPC  904  sends signaling to the VSP  900  so that it can get the call to the right PSAP  195 , but the location information itself is not sent back to the VSP  900 . Rather, just signaling codes necessary to route the VoIP E911 call to the proper selective router  140  and PSAP  195  (via an emergency services gateway  902 ) are sent from the VPC  904  to the VSP  900 . (An emergency services gateway (ESGW) is typically a function inside a standard media gateway. A media gateway is typically TCP/IP on one side, and TDM trunks on the other side.). 
     Location information itself in the embodiment of  FIG. 9  is maintained in a subscriber line database (SLDB), created from an out-of-band transaction. This means that the dual-mode phone user  190  presets their MSAG format location into the SLDB, e.g., by logging into a suitable SLDB portal during registration of their dual-mode phone, and enters their location (e.g., relevant street address). The PSAP  195  accesses this MSAG quality location information using a automatic location identificatier (ALI) query to the VPC  904 , which in turn pulls location data from the SLDB, formats it, and provides it back to the PSAP  195 . 
     Trials have been conducted in which a local exchange carrier (LEC) has permitted access to a selective router for the E911 network via the PSTN. In this trial, the LEC designated a specific 10-digit telephone number. A caller has their emergency call transferred to this 10-digit telephone number, which is then call-forwarded within the central office to the selective router, which then forwards the call to the correct PSAP based upon the digits dialed. However, this solution suffers the same significant drawbacks as that shown in  FIG. 7 , i.e., that callback number and location are not provided to the responsible PSAP. 
     Thus while carriers continue to accommodate and indeed foster development of a nationwide VoIP telephone network, difficulties nevertheless abound, particularly with respect to provision of location of a VoIP caller to an emergency response center. As a result, wireless carriers wishing to offer dual-mode phones to customers must make significant technology investments and infrastructure upgrades to handle VoIP calls. (Dual-mode phones are capable of initiating mobile E9-1-1 calls using, e.g., Global System for Mobile Communications (GSM) or code division, multiple access (CDMA), or even wireless fidelity (WiFi)). The desire is to handle use of such technologies in a VoIP communications network. However, the reality is that many wireless carriers continue to utilize switched technology equipment at least at the front end in communication with a VoIP caller. If an E911 call is placed, it is likely handled in the wireless carrier&#39;s network from a circuit switched interface. The present inventors realize that this causes a delay in the introduction of VoIP technology, and reduced competition from other carriers. Moreover, full compliance with national requirements may not be possible, e.g., the need to provide location and callback information. 
     There is the need for a simple and effective solution to providing easy and full access to the Enhanced 911 network of an emergency services provider (e.g., PSAP) from wireless VoIP users of a carrier utilizing a switched network. 
     SUMMARY OF THE INVENTION 
     In accordance with the principles of the present invention, a call protocol conversion gateway comprising a module adapted to receive signaling system number 7 (SS7)—based call signaling. Another module is adapted to convert the SS7 MAP/Lg+ based call signaling into session initiation protocol (SIP)-based call signaling, and yet another module is adapted to pass the SIP call signaling to a voice over Internet (VoIP) positioning center. 
     A method of converting a VoIP call, passed over a switched telephone network, into a VoIP call for presentation to a public safety access point (PSAP) in accordance with another aspect of the invention comprises receiving a voice over Internet protocol (VoIP) call from a VoIP phone via a local area network. The VoIP call is routed using signaling system number 7 (SS7) MAP/Lg+ based call signaling. The SS7 MAP/Lg+ based call signaling is converted into session initiation protocol (SIP) call signaling. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing relevant software elements including an SS7 based ANSI-41 J-STD-036 to SIP protocol conversion gateway used to handle placement of an E911 call from a VoIP user through a wireless carrier including switched network components, in accordance with the principles of the present invention. 
         FIG. 2  is a call flow diagram showing relevant call flow with respect to the use of an SS7 based ANSI-41 J-STD-036 to SIP protocol conversion gateway, in accordance with the embodiment shown in  FIG. 1 . 
         FIG. 3  is a block diagram showing relevant software elements including an SS7 based MAP-Lg+ to SIP protocol conversion gateway used to handle placement of an E911 call from a VoIP user through a wireless carrier including switched network components, in accordance with the principles of the present invention. 
         FIG. 4  is a call flow diagram showing relevant call flow with respect to the use of an SS7 based MAP-Lg+ to SIP protocol conversion gateway, in accordance with the embodiment shown in  FIG. 3 . 
         FIG. 5  is a block diagram showing relevant software elements including an SS7 based ISUP to SIP protocol conversion gateway used to handle placement of an E911 call from a VoIP user through a wireless carrier including switched network components, in accordance with the principles of the present invention. 
         FIG. 6  is a call flow diagram showing relevant call flow with respect to the use of an SS7 based ISUP to SIP protocol conversion gateway, in accordance with the embodiment shown in  FIG. 5 . 
         FIG. 7A  shows conventional relevant systems in an emergency 911 call made via a wireless caller in a GSM network. 
         FIG. 7B  shows conventional relevant systems in an emergency 911 call made via a wireless caller in a CDMA or TDMA network. 
         FIG. 8  shows one conventional solution to delivery of location data in wireless E911 format, but providing only latitude/longitude (lat/lon) location information. 
         FIG. 9  shows a conventional delivery of location data in MSAG format for VoIP calls for processing E911 calls using the NENA approved i2 call flow. 
     
    
    
     DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS 
     The present invention provides a signaling system number 7 (SS7) gateway device that translates between circuit-switched SS7 protocols and session initiation protocol (SIP) oriented protocol, allowing an E911 call initiated over a switched network to be routed by a VoIP network. 
     Use of an SS7 based gateway in accordance with the principles of the present invention, as opposed to the ORREQ technique shown in  FIG. 8 , or the SIP Invite technique shown in  FIG. 9 , is that it provides a PSAP with MSAG quality data without the need for carrier&#39;s to invest in building out a VoIP core. The SS7 gateway approach forms a marriage of the best features of the embodiments of  FIGS. 8 and 9 . This saves wireless carriers significant amounts of cash because they don&#39;t need to switch to a VoIP core (as in  FIG. 9 ) to have the capability to provide MSAG quality location information over a TDM network (such as the one shown in  FIG. 8 ). This allows carriers to keep their existing networks, while at the same time adding MSAG location capabilities for WiFi users, all at minimal infrastructure cost. 
     The consumer benefits as well, as use of an SS7 gateway in a TDM network provides emergency services with a high quality MSAG type location rather than just a lat/long quality location, when in their time of need. 
     Using todays systems, most wireless carriers provide lat/lon quality information for all WiFi callers. While lat/lon information (e.g., cell tower location, etc.) is somewhat accurate, it does not give emergency services personnel total comfort in their locating the caller in a timely fashion. However, using an SS7 based gateway inserted into a VoIP platform including a voice positioning center (VPC), users can use a dual mode phone, dial 911, and MSAG quality location information can be provided to the designated PSAP, all without significant investment in a VoIP core by the wireless carrier. The home or office address (MSAG quality location information) can be given because it&#39;s based on the VoIP network. 
     Thus, wireless carriers may continue signaling the way they are today, i.e., using the J-STD-036 standard for CDMA and GSM in North America, but see benefits of a VoIP network core, i.e., provision of MSAG quality location data to a PSAP. 
     In one aspect of the invention, SS7 based J-STD-036/Transaction Capabilities Application Part (TCAP) signaling is translated to SIP for purposes of E911 call routing. 
       FIG. 1  is a block diagram showing relevant software elements including an SS7 based ANSI-41 J-STD-036 to SIP protocol conversion gateway used to handle placement of an E911 call from a VoIP user through a wireless carrier including switched network components, in accordance with the principles of the present invention. 
     In particular, as shown in  FIG. 1 , a wireless VoIP user  190  places a 911 call, which is serviced by a user agent  180 . The user agent  180  gains access to the wired Internet via a WiFi access point  170 , and access to the wireless carrier&#39;s network via a wireless VoIP base station controller  160 . 
     From the wireless VoIP base station controller  160 , the VoIP 911 call over a WiFi network is routed to the wireless carrier&#39;s Mobile Switching Center (MSC)  150 . Ultimately, the 911 call is routed to an appropriate selective router  140 , and then to the proper PSAP E911 network  195 . 
     Importantly, in accordance with the principles of the present invention, 911 calls from the wireless MSC  150  are processed by an SS7 to SIP gateway  100  that accepts and sends SS7 TCAP [Transaction Capability Application Part]/J-STD-036 based signaling, but gateways the call signaling to session initiation protocol (SIP) signaling. Thus, the SS7 to SIP gateway  100  communicates with the MSC  150  to translate from J-STD-036 TCAP to SIP, i.e., between wireless technologies and VoIP location technologies. 
     Preferably the SIP signaling is compliant to a relevant standard, but there is currently no existing standardized SS7 interfaces allowed by the current standards for VoIP E911, i.e., National Emergency Number Association (NENA) i1/i2 standards for a voice over IP (VoIP) positioning center (VPC). 
     The SS7 to SIP gateway  100  translates call data received from the MSC  150  (e.g., calling party number) into relevant SIP INVITE parameters. The call data is then passed to a voice over Internet protocol (VoIP) positioning center (VPC)  120  as a VoIP call. 
     The VPC  120  is an application that determines the appropriate PSAP, based on the location of the 911 caller  190 , returns associated routing instructions to the VoIP network, and provides the callback number to the PSAP  195  through an automatic location identifier (ALI). (An ALI is a database that relates a specific telephone number to an address. This database accepts a PSAP query with a telephone number and responds with an address. In the case of an ESQK, the ALI database steers (redirects) the query to the appropriate VoIP positioning center and steers the response back to the querying PSAP). 
     The SIP INVITE command from the SS7 to SIP gateway  100  preferably includes the following parameters:
         a) The “from” field
           =the dialed digits from the VoIP caller  190 
               (NPA-xxx-yyyy)   
               b) The “to” field
               =911   
               c) The CBN field
               =callback number of the VoIP caller  190     
               
               

     The SS7 to SIP gateway  100  receives routing instruction from the VoIP positioning center (VPC)  120  and sends the routing key (e.g., emergency services query key (ESQK), a trunk select code (e.g., emergency services routing number (ESRN)), and optionally an i1 public switched telephone network (PSTN) number (e.g., last routing option (LRO)) back to the MSC  150 . (The ESRN is a 10-digit number that specifies the selective router  140  to be used to route a call. The LRO is routing information sent by the VPC  120  that provides a “last chance” destination for a call, for example the contingency routing number (CRN) or a routing number associated with a national call center.). 
     The call then proceeds as it otherwise would for a wireless E911 call. 
       FIG. 2  is a call flow diagram showing relevant call flow with respect to the use of an SS7 based ANSI-41 J-STD-036 to SIP protocol conversion gateway, in accordance with the embodiment shown in  FIG. 1 . 
     In particular, as shown in step  101  of  FIG. 2 , a caller  190  makes an E911 call while connected via a wireless IP based network. 
     The E911 call requires routing to a Public Safety Answering Point (PSAP)  195  based upon the street address of the caller (e.g., MSAG quality location data), which may be provisioned beforehand by the service provider based on, e.g., a billing address, etc. Alternatively, the E911 call can be routed to the correct PSAP  195  based on the absolute location of the caller, e.g., as determined by received data about their wireless access node such as wireless fidelity (WiFi) access point  170 . 
     The MSC  150  sends out signaling data related to the wireless E911 call using the J-STD-036/TCAP protocol standard, including use of a TCAP message OriginationRequest (ORREQ). The TCAP OriginationRequest message should contain the calling party&#39;s number (CgPN) and called pary number (e.g., 911, etc.). 
     In step  102  of  FIG. 2 , the SS7 to SIP gateway  100  translates received J-STD-036/TCAP parameters into session initiation protocol (IETF), i.e., into SIP INVITE parameters. 
     In step  103  of  FIG. 2 , the VoIP positioning center (VPC)  120  assigns routing based upon the location retrieved from the location information service/subscriber line database (LIS/SLDB)  130 . 
     Preferably the SLDB is configured so that no modifications are required to the core conventional existing VoIP E9-1-1 network. The SLDB  130  is used to relate a Session Initiated Protocol (SIP) Universal Resource Identifier (URI) or a telephone number to a PSAP. In databases that use tables in lieu of GIS for routing determination, the address of the “subscriber” can be any valid street address within the jurisdiction of the PSAP. 
     In step  104  of  FIG. 2 , the SS7 to SIP gateway  100  receives routing instruction from the VoIP positioning center (VPC)  120 , including an emergency services query key (ESQK) and an emergency services routing number (ESRN), and translates these NENA i2 standard elements into wireless E911 elements, e.g., ESQK=ESRK; ESRN=Trunk select code; and, optionally an i1 PSTN number, e.g., (LRO)). 
     In step  105  of  FIG. 2 , the MSC  150  then egresses the call based upon the ESRK and the trunk select code for use by the selective router  140 . The selected selective router  140  delivers the call to the assigned PSAP, e.g., PSAP  195 , based upon the ESRK. 
     In another aspect of the invention, SS7 based TCAP/MAP/Lg+ signaling is translated to SIP for purposes of E911 call routing. 
       FIG. 3  is a block diagram showing relevant software elements including an SS7 based MAP-Lg+ to SIP protocol conversion gateway used to handle placement of an E911 call from a VoIP user through a wireless carrier including switched network components, in accordance with the principles of the present invention. 
     In particular,  FIG. 3  shows calls from a wireless MSC processed by a SS7 to SIP gateway  200  that accepts and sends SS7 TCAP (Transaction Capability Application Part)/MAP based signaling (Lg+ interface), but gateways the signaling to SIP protocol signaling. Again, ideally the SIP signaling is compliant to a relevant standard for SIP signaling in a VoIP network, if existing and in place. 
     The 911 call from the wireless VoIP user  190  is routed to the wireless carrier&#39;s Mobile Switching Center (MSC)  150  via a user agent  180  for the wireless VoIP device, a WiFi access point  170 , and a UMA network controller UNC  220 . 
     This aspect of the invention creates an SS7 based gateway  200  that translates from mobile application part; interface specification Lg+ (MAP Lg+) to SIP. The SS7 based MAP-Lg+ to SIP gateway  200  is in communication with the MSC  150 , and serves as a translator between wireless technologies and VoIP location technologies. 
     The SS7 based MAP-Lg+ to SIP gateway  200  translates the call data received from the MSC  150  (e.g., calling party number) into SIP INVITE parameters, which are then passed to a VPC  120  as a voice over IP (VoIP) call. 
     The SS7 based MAP-Lg+ to SIP gateway  200  receives routing instruction from the VPC  120  and sends a routing key (e.g., an emergency services query key (ESQK), trunk select code (e.g., emergency services routing number (ESRN), and (optionally) an i1 public switched telephone network (PSTN) number, e.g., last routing option (LRO) back to the MSC  150 . The 911 call then proceeds as it would otherwise for a wireless E911 call. 
       FIG. 4  is a call flow diagram showing relevant call flow with respect to the use of an SS7 based MAP-Lg+ to SIP protocol conversion gateway  200 , in accordance with the embodiment shown in  FIG. 3 . 
     In particular, as shown in step  201  of  FIG. 4 , a caller makes an E911 call while connected via a wireless IP based network. The 911 call requires routing to a public safety answering point (PSAP) based upon the street address of the wireless VoIP caller  190  (which is provisioned beforehand), or their absolute location (determined by received data about the wireless access node associated with the WiFi access point  170 . 
     The MSC  150  sends out signaling data related to the VoIP 911 call over a WiFi network using MAP/Lg+. Preferably the MAP message, i.e., “SubscriberLocation Report (SLR)” contains the calling party number (CgPN) and called party number (i.e., 911 etc). 
     In step  202  of  FIG. 4 , the SS7 based MAP-Lg+ to SIP conversion gateway  200  translates received MAP/Lg+ parameters into SIP INVITE parameters. 
     In step  203  of  FIG. 4 , the VPC  120  assigns routing based upon the location retrieved from the relevant location information server (LIS)/subscriber line database (SLDB). 
     In step  204  of  FIG. 4 , the SS7 based MAP-Lg+ to SIP conversion gateway  200  receives routing instruction from the VPC  120  (e.g., an emergency services query key (ESQK) and an emergency services routing number (ESRN), and translates these NENA i2 standard elements into Wireless E9-1-1 elements. For instance, the ESQK is translated into an emergency services routing key (ESRK), the ESRN is translated into a trunk select code for use by the selective router  140 , and optionally an i1 PSTN phone number, e.g., last routing option (LRO). 
     In step  205  of  FIG. 4 , the MSC  150  then egresses the 911 call based upon the ESRK and the trunk select information to the relevant selective router  140 , which delivers the 911 call to the PSAP based upon the ESRK. 
     In yet another aspect of the invention, SS7 based ISUP signaling is translated to SIP, e.g., for purposes of E911 call routing. 
       FIG. 5  is a block diagram showing relevant software elements including an SS7 based ISUP to SIP protocol conversion gateway used to handle placement of an E911 call from a VoIP user through a wireless carrier including switched network components, in accordance with the principles of the present invention. 
     In particular,  FIG. 5  shows calls handled by a wireless MSC  150  are processed by an SS7 based ISUP to SIP conversion gateway  300  that accepts and sends SS7 ISUP based signaling, but gateways the signaling to SIP signaling. Preferably, the SIP signaling to which the SS7 based ISUP to SIP conversion gateway  300  converts is fully compliant to any applicable standard, if available. 
     The 911 call from the wireless VoIP user  190  is routed to the wireless carrier&#39;s Mobile Switching Center (MSC)  150  as shown. The SS7 based ISUP to SIP conversion gateway  300  then translates from integrated services user part (ISUP) protocols into SIP protocol signaling. 
     The SS7 based ISUP to SIP conversion gateway  300  is in communication with the MSC  150 , and serves as a translator between wireless and VoIP location technologies. The SS7 based ISUP to SIP conversion gateway  300  translates call data received from the MSC  150  (e.g., calling party number) into appropriate SIP INVITE parameters, which are then passed to the VPC  120  as a VoIP call. 
     The SS7 based ISUP to SIP conversion gateway  300  receives routing instruction from the VPC  120  and sends the routing key (e.g., the emergency services query key (ESQK), trunk select code (e.g., emergency services routing number (ESRN), and (optionally) an i1 public switched telephone network (PSTN) phone number, e.g., last routing option (LRO) back to the MSC  150 . The VoIP/WiFi 911 call then proceeds as it would for a wireless E911 call. 
       FIG. 6  is a call flow diagram showing relevant call flow with respect to the use of an SS7 based ISUP to SIP protocol conversion gateway  300 , in accordance with the embodiment shown in  FIG. 5 . 
     In particular, as shown in step  301  of  FIG. 6 , a caller makes an E911 call while connected via a wireless IP based network (e.g., WiFi). The call requires routing to an appropriate public safety answering point (PSAP) based upon the street address of the dual-mode phone user  190  (which is provisioned beforehand), or their absolute location (e.g., determined by received data about the lat/lon of the WiFi wireless access node  170 . 
     The MSC  150  sends out signaling data related to the call using ISUP. Preferably, the IAM contains the calling party number (CgPN) and called party number (e.g., 911, 411, etc.). 
     In step  302  of  FIG. 6 , the SS7 based ISUP to SIP conversion gateway  300  translates received ISUP IAM parameters into relevant SIP INVITE parameters. 
     In step  303  of  FIG. 6 , the VPC  120  assigns routing based upon the location retrieved from the location information server (LIS) or subscriber line database (SLDB)  130 . 
     In step  304  of  FIG. 6 , the SS7 based ISUP to SIP conversion gateway  300  receives routing instruction from the VPC  120 . Exemplary routing instruction includes an emergency services query key (ESQK) and an emergency services routing number (ESRN), and translates these NENA i2 standard elements into Wireless E9-1-1 elements. For instance, an ESQK is translated into an emergency services routing key (ESRK), an ESRN is converted into a trunk select code for the relevant selective router  140 , and optionally an i1 PSTN number, e.g., last routing option (LRO). 
     In step  305  of  FIG. 6 , the MSC  150  then egresses the call to the proper selective router  140  based upon the ESRK and trunk select information. The selective router  140  then delivers the E911 call to the proper PSAP  195  based upon the ESRK information. 
     Accordingly, use of an SS7 to SIP conversion gateway in accordance with the principles of the present invention provides for a low cost architecture that has the ability to ease the transition from circuit switched routing of wireless calls (including emergency calls such as E911) to Internet Protocol (IP) based routing of wireless calls (i.e., voice over IP (VoIP)). 
     The invention has applicability to wireless carriers, and in particular to the use of dual-mode phones over local area wireless networks such as WiFi networks. 
     While the invention has been described with reference to the exemplary embodiments thereof, those skilled in the art will be able to make various modifications to the described embodiments of the invention without departing from the true spirit and scope of the invention.