Abstract:
A secondary directory telephone number (SDN) is assigned either to each voice over IP (VOIP) IP port utilized by subscribers or to each public safety access point (PSAP). The SDN, MAC address of the IP port accessed by a subscriber, and geographic location of the SDN or MAC address are stored in a database. This information is accessed by the PSAP based on SDN or MAC address to obtain the location of a VOIP subscriber to facilitate providing emergency services in response to a 911 call by a VOIP subscriber.

Description:
BACKGROUND 
     The present invention is directed to providing emergency “911” services for Internet protocol (IP) telephones, and is more specifically directed to resolving the location of IP telephones in order to provide emergency services in response to a 911 call. 
     Emergency services are available in the United States by dialing “911” from a conventional wireline telephone. Such calls are routed to a public safety answering point (PSAP) based on the telephone number of the calling party which is available by calling line identification (CLI). The telephone number of the calling party is used to determine the appropriate PSAP, normally the closest PSAP to the calling party, to receive the emergency call. An automatic location identifier (ALI) database in the public switched telephone network (PSTN) contains records that associate telephone numbers to geographic locations. 
     The availability of 911 emergency services is complicated by the growing popularity of IP telephones. Because an IP telephone can be moved by the user to any available IP port maintained by the provider of IP telephony services subscribed to by the user, the directory number (DN) assigned to an IP telephone cannot be assumed to correspond with a specific location of the user. For example, an employee normally uses his IP phone in a home office in Chicago but elects to take the IP phone to a remote office in New York City that also supports IP telephony services for the company. The telephone number of the IP phone does not change when it is used in New York City by the employee. Hence, the telephone numbers of IP phones cannot be relied upon to determine the current location of the user. 
     It is important to be able to automatically determine the geographic location of the user associated with a 911 call since the user may become incapacitated or otherwise not available to provide location information to a 911 operator. Thus, there exists a need to be able to determine the geographic location of IP telephone users requesting emergency 911 services. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a solution to this problem. 
     In accordance with an embodiment of the present invention, a secondary directory telephone number (SDN) is assigned to each IP port that is enabled for voice over IP (VOIP). A database contains a record of each SDN and its fixed Media Access Control (MAC) address. Upon initial registration of an IP telephone at a supported port, the supporting telecommunication switch stores the SDN as well as the DN for the IP telephone. Upon a 911 call from the IP telephone, the switch retrieves the corresponding SDN and uses the SDN to determine the PSAP to route the call for handling since geographic location is associated with the SDN, i.e. the physical location of the port and not the specific IP phone utilizing the port. The SDN, and preferably the DN, are provided to the PSAP. The PSAP uses the SDN to query a database to retrieve corresponding location information of the subscriber requesting emergency services. 
     In accordance with another embodiment of the present invention, an SDN is assigned for each PSAP, and one of the SDNs is assigned to each IP port. Thus, multiple MAC addresses corresponding to different IP ports can be assigned the same SDN that will be used to route the emergency 911 calls to the specific PSAP associated with the single SDN. Upon initial registration of an IP phone at a supported port, the supporting telecommunication switch will store the SDN, MAC address, and DN for the IP user. Upon a 911 call from the IP phone, the switch retrieves the corresponding SDN based on DN or IP address and uses the SDN to determine the associated PSAP to receive the call. The MAC address and DN are provided to the PSAP. The PSAP retrieves the specific location of the IP telephone from a database by sending a query based on the MAC address since the SDNs are not location specific in this embodiment. Advantageously this embodiment does not require a different SDN to be assigned to each IP port, and thus minimizes the number of additional telephone numbers required to be assigned. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of an exemplary telephony network suited for supporting an embodiment of the present invention. 
         FIG. 2  is a flow diagram illustrating an exemplary method in accordance with the present invention. 
         FIG. 3  is a flow diagram illustrating another exemplary method in accordance with the present invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a telecommunications system  10  in which the arrows pointing from dashed lines  12  and  14  indicate different geographic regions such as Chicago and New York City, respectively. In the geographic region represented by line  12 , a plurality of PSAPs represented by PSAP  16  and  18  are supported by a tandem switch  20  that supports the routing of 911 emergency calls to one of the PSAPs. An IP telephone  22  is connected to an IP port enabled for VOIP of client server  23 , e.g. a hub or Ethernet switch. A laptop computer  24  is also enabled to support VOIP and is connected to a port of client server  23  with VOIP capability. A location resolution database (LRD)  26  stores information relating to SDNs and the corresponding fixed MAC addresses of the VOIP enabled ports. 
     In the geographic region represented by line  14 , the illustrated telecommunication elements are identical to those shown in geographic region  12 . The PSAPs  30  and  32  are supported by tandem switch  34  that supports the route routing of 911 emergency calls to one of the PSAPs. An IP telephone  36  is connected to an IP port enabled for VOIP of client server  37 . A laptop computer  38 , also enabled to support VOIP, is supported by a VOIP capable port of client server  37 . A LRD  40  stores information relating to SDNs and the corresponding MAC addresses of the VOIP enabled ports. As used herein an “IP telephone” is intended to encompass all devices that support VOIP. 
     A telecommunication switch  42  capable of supporting VOIP is connected to tandem switches  20  and  34 , a subscriber database  44 , and automatic location identifier (ALI) database  46 . The switch  42  is also connected to the IP network, e.g. the internet,  48  that serves as a communication backbone to transport VOIP traffic between switch  42  and exemplary VOIP users  22 ,  24 ,  36  and  38  via client servers  23  and  37 . Communications between switch  42  and the exemplary LRDs  26  and  40  are also carried via Internet  48 . Registration host  50  is connected to the internet  48  and serves as a centralized node for authenticating and registering valid VOIP users. Typically registration host  50  will serve a community of users such as employees of a company. Although elements  42 ,  44 ,  46  and  50  are shown as being in a geographic region outside of regions  12  and  14 , it will be apparent to those skilled in the art that these elements could also be located within either region  12  or  14 . 
     First Embodiment: SDN Assigned for Each VOIP Port 
     In this exemplary method an IP subscriber is a member of a company with his office in region  12 , e.g. Chicago. The subscriber is on a business trip at a company office in region  14 , e.g. New York City, and has carried his laptop computer  38  that is VOIP enabled. The enterprise network administrator has assigned an SDN for each VOIP enabled port, and caused this information along with the corresponding MAC address for each VOIP enabled port to be stored in LRD  26 . This information along with location information for each VOIP enabled IP port is also stored in the ALI database  46 . 
     As shown in  FIG. 2 , the subscriber connects his laptop computer  38  to a VOIP enabled IP access port supported by client server  37  to initiate registration in order to receive VOIP services at step  52 . In step  54  the registration host  50  receives a first registration request and uses the received MAC address of the accessed IP port to locate an assigned corresponding SDN. This involves the registration host transmitting a query based on the MAC address of the IP port to the LRD  26  that contains the corresponding record. Where multiple or distributed LRDs are used in the network, the registration host can either determine which LRD to query, e.g. based on the DN and/or MAC address, or send a query to each LRD and await the LRD with the record to respond with the appropriate information. The LRD  26  locates the record corresponding to the IP MAC address and transmits the corresponding SDN in response to the query. In step  56  the registration host  50  sends a second registration request to switch  42 ; the second registration request includes the DN and SDN of the subscriber requesting service. The switch  42  locates the corresponding record in subscriber database  44  based on DN and stores the SDN in step  58 . 
     In step  60  the subscriber  38  initiates an emergency request using VOIP supported by his laptop computer by dialing 911. In step  62  switch  42  receives the emergency call request including the DN of the calling party, retrieves the corresponding SDN for the subscriber from the subscriber database  44 , and determines that the tandem switch  34  is the appropriate tandem switch for call routing. The switch  42  sends the calling party&#39;s DN and SDN to tandem switch  34  in step  64 . In step  66  the tandem switch  34  routes the call to PSAP  32  based on the SDN. In step  68  PSAP  32  receives the emergency call request that includes the calling party&#39;s DN and SDN. The PSAP  32  uses the SDN to retrieve address and location data of the caller from ALI database  46  in step  70 . Since the SDN is unique and has a corresponding MAC address stored in the ALI database during registration, location can be determined based on the fixed MAC address for the port in use by the calling party, or alternatively location information can be stored in the ALI for direct retrieval. If a call disconnect occurs before the PSAP operator obtained the necessary information from a conversation with the calling party, the operator places a return call using the calling party&#39;s DN in step  72 . The return call is routed by switch  42  to the calling party  38  in step  74 . The PSAP operator gathers the necessary information from the calling party and dispatches appropriate emergency personnel in step  76 . 
     It will be apparent that steps  72 ,  74  and  76  will not be required if the PSAP operator obtains the necessary information from the calling party without a call disconnect occurring. Alternatively, the operator can dispatch a default emergency team if a conversation with the calling party is not possible, e.g. calling party is unable to speak or speaks a language not understood by the operator. These additional steps are shown to illustrate the ability of a PSAP operator to initiate a return call based on the DN of the calling party even though the SDN associated with the calling party was utilized to identify the appropriate PSAP to handle the call. This embodiment does not require any changes to the ALI database. 
     Second Embodiment: SDN Assigned for Each PSAP 
     Similar to the first embodiment an IP subscriber is a member of a company with his office in region  12 , e.g. Chicago. The subscriber is on a business trip at a company office in region  14 , e.g. New York City, and has carried his laptop computer  38  that is VOIP enabled. However, in this embodiment the enterprise network administrator has assigned an SDN for each PSAP instead of assigning a different SDN for each VOIP port. The assigned SDN and MAC address for each VOIP port are stored in LRD  26 . This information along with location information for each VOIP enabled IP port is also stored in the ALI database  46 . 
     As shown in  FIG. 3 , the subscriber connects his laptop computer  38  to a VOIP enabled IP access point supported by client server  37  to initiate registration in order to receive VOIP services at step  100 . In step  104  the registration host  50  receives a first registration request and uses the received MAC address of the accessed IP port to locate an assigned SDN. This involves the registration host transmitting a query based on the MAC address of the IP port to the LRD  26  that contains the corresponding record. Where multiple or distributed LRDs are used in the network, the registration host can either determine which LRD to query, e.g. based on the DN and/or MAC address, or send a query to each LRD and await the LRD with the record to respond with the appropriate information. The LRD  26  locates the record corresponding to the IP MAC address and transmits the corresponding SDN in response to the query. In step  104  the registration host  50  sends a second registration request to switch  42 ; the second registration request includes the DN, MAC address and SDN of the subscriber requesting service. The switch  42  locates the corresponding record in subscriber database  44  based on DN and stores the SDN in step  106 . 
     In step  108  the subscriber  38  initiates an emergency request for services using VOIP supported by his laptop computer by dialing 911. In step  110  switch  42  receives the emergency call request, retrieves the corresponding SDN for the subscriber from the subscriber database  44  based on the DN or IP address, and determines that the tandem switch  34  is the appropriate tandem switch for call routing. The switch  42  sends the calling party&#39;s DN, SDN and MAC address to tandem switch  34  in step  112 . In step  114  the tandem switch  34  routes the call to PSAP  32  based on the SDN. In step  116  PSAP  32  receives the emergency 911 call that includes the calling party&#39;s DN and MAC address. The PSAP  32  uses the MAC address to retrieve the location of the caller from ALI database  46  in step  118 . Location can be determined based on the unique MAC address for the port in use by the calling party since location information is stored in the ALI database for each MAC address by the system administrator. If a call disconnect occurs before the PSAP operator obtained the necessary information from a conversation with the calling party, the operator places a return call using the calling party&#39;s DN in step  120 . The return call is routed by switch  42  to the calling party  38  in step  122 . The PSAP operator gathers the necessary information from the calling party and dispatches appropriate emergency personnel in step  124 . 
     It will be apparent that steps  120 ,  122  and  124  will not be required if the PSAP operator obtains the necessary information from the calling party without a called disconnect occurring. These additional steps are shown to illustrate the ability of a PSAP operator to initiate a return call based on the DN of the calling party even though the SDN associated with the calling party was utilized to identify the appropriate PSAP to handle the call. 
     In accordance with embodiments of the present invention, the registration procedure for the registration host and the switch will need to accommodate SDN and MAC address information as well as having the ability to query the LRD database. The registration message format will accommodate the transmission of SDN and MAC address information. The ALI database will need to accommodate records that include SDN and MAC addresses, as well as permitting records to be accessed based on queries for this information. 
     Various modifications of the embodiments as described above and shown in the drawings can be made by those skilled in the art without departing from the scope of the present invention. Depending on the capacity and intelligence associated with nodes as shown in  FIG. 1 , separate elements can be combined into a single node. The different geographic regions shown in  FIG. 1  are intended to aid in understanding implementations in which IP users may elect to connect VOIP enabled devices at IP ports other than a normal home port including ports that are geographical remote from the home port. Of course, the embodiments of the present invention also perform the desired functions if the subscriber is located at his home port. Depending upon the nodes available and desired network architecture, information can be stored in a central database or distributed among a variety of databases located throughout the network. Although only a single switch is utilized in the illustrative embodiment, it will be apparent that a plurality of switches may be utilized depending upon the size and capacity of the network to be supported. A variety of VOIP enabled devices including wireline and wireless devices can be utilized. 
     Although embodiments of the present invention have been described above and shown in the drawings, the scope of the invention is defined by the claims that follow.