Patent Publication Number: US-2007121642-A1

Title: Method and system for supporting an emergency call

Description:
FIELD OF THE INVENTION  
      The present invention relates generally to wireless networks, and more specifically to a method for supporting an emergency call in an Internet Protocol (IP) based system, such as a Wireless Local Area Network (WLAN) system.  
     BACKGROUND  
      In an emergency, people need the ability to quickly contact an appropriate agency, such as the police, the fire department, or an ambulance. For such situations, a single telephone number, such as 911, is provided to connect emergency calls from a communication device to an emergency call center.  
      In cellular telephony systems, cellular operators are required to connect emergency calls to the emergency call center even if the communication device is not subscribed to the cellular telephony system. Therefore, users of un-subscribed communication devices have limited access to the resources of cellular telephony systems. However, in some cases such as the absence of cellular coverage or insufficient cellular capacity, emergency calls may need to be supported by a Wireless Local Area Network (WLAN) system. The WLAN system may connect the communication device to its resources by using Voice over Internet Protocol (VoIP). Therefore, users of un-subscribed communication devices need to be provided with limited access to the WLAN VoIP system for emergency calls.  
      Using WLAN systems for supporting emergency calls is problematic, since, conventionally, WLAN systems provide users with complete access to resources available within the WLAN system. In such a case, users of unsubscribed communication devices would be able to access resources they are not authorized to access, and which do not correspond to the emergency calls.  
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
      The accompanying figures, where like reference numerals refer to identical or functionally similar elements throughout the separate views and which together with the detailed description below are incorporated in and form part of the specification, serve to further illustrate various embodiments and to explain various principles and advantages all in accordance with the present invention.  
       FIG. 1  illustrates communication between a communication device and an emergency call center via a communications network, in accordance with some embodiments of the present invention.  
       FIG. 2  is a flowchart illustrating a method for supporting an emergency call in a communication device, in accordance with some embodiments of the present invention.  
       FIG. 3  illustrates the communication network of  FIG. 1  for supporting an emergency call, in accordance with various embodiments of the present invention.  
       FIG. 4  is a flowchart illustrating a method for supporting an emergency call, in accordance with various embodiments of the present invention.  
       FIG. 5  is a flow diagram illustrating messaging between elements of the communication network of  FIG. 3 , in accordance with various embodiments of the method for supporting an emergency call. 
    
    
      Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and/or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments of the present invention. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are often not depicted in order to facilitate a less obstructed view of these various embodiments of the present invention. It will further be appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. It will also be understood that the terms and expressions used herein have the ordinary meaning as is accorded to such terms and expressions with respect to their corresponding respective areas of inquiry and study except where specific meanings have otherwise been set forth herein.  
     DETAILED DESCRIPTION  
      Before describing in detail embodiments that are in accordance with the present invention, it should be observed that the embodiments reside primarily in combinations of method steps and apparatus components related to supporting an emergency call. In this document, relational terms such as first and second, top and bottom, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms “comprises”, “comprising”, or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by “comprises . . . a” does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.  
      It will be appreciated that embodiments of the present invention described herein may be comprised of one or more conventional processors and unique stored program instructions that control the one or more processors to implement, in conjunction with certain non-processor circuits, some, most, or all of the functions of supporting an emergency call described herein. The non-processor circuits may include, but are not limited to, a radio receiver, a radio transmitter, signal drivers, clock circuits, power source circuits, and user input devices. As such, these functions may be interpreted as steps of a method for supporting an emergency call. Alternatively, some or all functions could be implemented by a state machine that has no stored program instructions, or in one or more application specific integrated circuits (ASICs), in which each function or some combinations of certain of the functions are implemented as custom logic. Of course, a combination of the two approaches could be used. Thus, methods and means for these functions have been described herein. Further, it is expected that one of ordinary skill, notwithstanding possibly significant effort and many design choices motivated by, for example, available time, current technology, and economic considerations, when guided by the concepts and principles disclosed herein will be readily capable of generating such software instructions and programs and ICs with minimal experimentation.  
      A method and system for supporting an emergency call while restricting access to all other resources of an Internet Protocol (IP) based system is disclosed. The method includes initiating an emergency call through an IP based system. The method further includes receiving authorization for restricted access to resources of the IP based system for the purpose of making the emergency call only.  
       FIG. 1  illustrates communication between a communication device  102  and an emergency call center  104  via a communication network  106 , in accordance with some embodiments of the present invention. Examples of the communication device  102  include, but are not limited to, a mobile phone, a third Generation Partnership Project (3GPP)-compliant mobile handset, a two-way pager, and a Personal Digital Assistant (PDA) wherein such example devices incorporate the ability to communicate through the IP based system  108 . The communication device  102  includes a processor  101  and communicates with the emergency call center  104  through a communication network  106 . The functions of the processor  101  will be described in conjunction with  FIG. 2 .  
      In an exemplary embodiment of the present invention, the communication network  106  includes an IP based system  108 , an IP network  109  and a cellular communication system  110 . Examples of the IP based system  108  may incorporate, but are not limited to, a Voice over Internet Protocol (VoIP), Internet Telephony, and WiFi. Examples of the IP Network  109  are a Digital Subscriber Line (DSL) network or a Hybrid Fiber Coaxial (HFC) Cable Network. Examples of the cellular communication system  110  include, but are not limited to, a Global System for Mobile Communications (GSM) network and a Code Division Multiple Access (CDMA) network. The communication device  102  is not subscribed to the IP based system  108 . The communication network  106  supports an emergency call, from the communication device  102 , even if the communication device  102  is not subscribed to the IP based system  108 .  
       FIG. 2  is a flowchart illustrating a method for supporting an emergency call from the communication device  102 , in accordance with some embodiments of the present invention. At step  202 , a user of the communication device  102  makes an emergency call by, for example, dialing 911 to place a call to the emergency call center  104 . The processor  101  initiates the emergency call through the IP based system  108 . In accordance with an embodiment of the present invention, the processor  101  initiates the emergency call by sending an Extensible Authentication Protocol (EAP) message to a gateway ( 306  in  FIG. 3 ). At step  204 , the processor  101  receives authorization for restricted access to the resources of the IP based system  108 , only for the purpose of making the emergency call. Therefore, the user of the communication device  102 , which is not subscribed to the IP based system  108 , is only authorized to access the resources of the IP based system  108 , to make the emergency call. Access to IP based resources corresponding to a non-emergency call is denied. At step  206 , the processor  101  receives authorization for restricted access to the resources of the cellular communication system  110 , only for the purpose of completing the emergency call. The user of the communication device  102  is only authorized to access the resources of the cellular communication system  110 , for the purpose of completing the emergency call. Access to Cellular Communication System resources corresponding to a non-emergency call is denied.  
       FIG. 3  illustrates a system  300  for supporting an emergency call, in accordance with some embodiments of the present invention. The system  300  includes the communication device  102 , the IP based system  108 , the IP Network  109 , the cellular communication system  110 , and a Public Switched Telephone Network (PSTN)  304 . The IP based system  108  includes an Access Point  302  coupled to a gateway  306 . The gateway  306  includes a processor  308 . Details regarding the functions of these elements as they pertain to the present invention will be provided in conjunction with the descriptions of  FIGS. 4 and 5 .  
      In one embodiment, the IP Network  109  is a DSL network. A DSL network, as commonly known in the art, typically includes a Digital Subscriber Line Access Multiplier (DSLAM), such as a Broadband Digital Terminal/Universal Services Access Multiplier (BDT/USAM) commercially available from Motorola, Inc.; routers, and support servers such as Domain Name Server (DNS), Authentication Authorization and Accounting (AAA), and the like. The Customer Premise Equipment (CPE) portion of the DSL network (DSL router) can be either embedded in the gateway  306  or can be an external device in the home.  
      In another embodiment, the IP Network  109  is a HFC Cable network. A HFC Cable network, as commonly known in the art, typically includes a Cable Modem Termination System (CMTS), such as the BSR64000, commercially available from Motorola, Inc; routers, and support servers such as DNS, AAA, and the like. The cable modem is either embedded in the gateway  406  or would be an external device in the home. In both the DSL or HFC Cable Network case, the IP Network  109  provides access (routing) between the IP based system  108  and other IP entities including the (PDG)  310 .  
      The cellular communication system  110  includes a Packet Data Gateway (PDG)  310 , an AAA server  312 , a Home Subscriber Server (HSS)  313  and a Call Session Control Function (CSCF)  314 . Details regarding the functions of these elements as they pertain to the present invention will be provided in conjunction with the descriptions of  FIGS. 4 and 5 .  
       FIG. 4  is a flowchart illustrating a method for supporting the emergency call, in accordance with various embodiments of the present invention. The method will now be described in conjunction with  FIG. 3 . At step  402 , the processor  308 , present in the gateway  306 , receives a request to authorize the emergency call. The user of the communication device  102  sends the request. The communication device  102  is not subscribed to the IP based system  108 . In accordance with an embodiment of the present invention, the request is an Extensible Authentication Protocol (EAP) message, specifying that the emergency call requires authentication. In accordance with an embodiment of the present invention, the processor  308  determines that the communication device  102  is not subscribed to the IP based system  108  by interrogating the AAA server  312 .  
      At step  404 , the processor  308  authorizes the user of the communication device  102  restricted access to the resources of the IP based system  108 , only for the purpose of making the emergency call. The user of the communication device  102 , being a non-subscriber of the IP based system  108 , is only allowed to access those resources of the IP based system  108  that correspond to the emergency call. The processor  308  authorizes the user of the communication device  102  by associating the communication device  102  with an access point  302 . In accordance with an embodiment of the present invention, the access point is a WLAN access point.  
      At step  406 , the processor  308  receives authorization for the user of the communication device  102  to gain restricted access to the resources of the cellular communication system  110 . This authorization is for the purpose of completing the emergency call to the emergency call center  104 . Access to the resources of the cellular communication system  110  for completing a non-emergency call, is denied. In one embodiment of the present invention, the AAA server  312  authorizes the user of the communication device  102  after receiving notification messages from the processor  308 . The notification messages from the processor  308  notify the AAA server  312  about the request for the emergency call.  
      Turning now to  FIG. 5 , detailed messaging between the elements of  FIG. 3  to implement an embodiment of the method of supporting an emergency call will be described. At step  502 , the communication device  102  sends a message to the gateway  306  to inform the gateway  306  that an emergency call requires special authorization. In the present embodiment, the message is an EAP message. Upon receiving the notification, at step  504 , the gateway  306  will authorize the emergency call by allowing the communication device  102  to associate with the IP based system&#39;s access point  302 . At step  504 , the gateway  306  also sends a message to the AAA server  312  in the cellular communication system  110  to notify it of the emergency call. In accordance with an embodiment of the present invention the emergency call is identified based on an International Mobile Station Identity (IMSI) associated with the communication device  102  that made a request for the emergency call. In accordance with one embodiment, the AAA server  312  is notified using a Remote Authentication Dial-in User Service (RADIUS) message. At step  506 , the AAA server  312  subsequently sends a message to the HSS  313  to notify the HSS  313  of the emergency call. Subsequent to step  506  and prior to the SIP registration process beginning (step  518 ), the HSS  313  notifies the CSCF  314  about the emergency call and authorizes the call by sending a notification message to the CSCF  314  (step  507 ). This causes the CSCF  314  to reject all non-emergency calls. At step  508 , the AAA server  312  notifies the PDG  310  about the emergency call. In accordance with an embodiment of the present invention, the AAA server uses a RADIUS message to notify the PDG  310  about the emergency call. Meanwhile, at steps  510  and  512 , the communication device  102  obtains a local IP address through the DHCP (not shown). Further, at steps  514  and  516 , the communication device  102  and the PDG  310  go through EAP-Authentication Key Agreement (EAP-AKA) within Internet Key Exchange version 2 (IKEv2) to establish an IPsec security association.  
      When the security association is completed at the PDG  310 , registration of the communication device  102  commences at step  518 . In accordance with an embodiment of the present invention, the registration is a Session Initiation Protocol (SIP) registration. The processor  308 , present in the gateway  306 , directs all traffic related to SIP signaling for the emergency call to the PDG  310  (step  522 ). At the same time, the processor  308  drops data packets that are addressed to locations other than the PDG  310 . The CSCF  314  ensures that only an emergency call established to the Emergency Call Center  104  via the Public Switched Telephone Network (PSTN)  304  through a media gateway.  
      After SIP registration and SIP INVITE processing is completed (steps  522  and  523 ) and the CSCF  314  establishes the emergency call to the Emergency Call Center  104 , the CSCF  314  redirects the voice bearer of the emergency call to the media gateway for the emergency call (step  524 ). At step  526 , the PDG  310  routes the voice bearer packet data from the communication device  102  directly to the media gateway, without the voice bearer packet passing through the CSCF  314 . The PDG  310  routes the voice signaling packet data from the communication device  102  directly to the CSCF  314  (step  526 ). The PDG  310  restricts all other packet data from the communication device  102  to prevent unauthorized usage of cellular communication system  110  resources. To accomplish this, the PDG  310  is informed of the Internet Protocol (IP) address of the media gateway and CSCF  314  for the emergency call by the HSS. In accordance with an embodiment of the present invention, the PDG  310  is pre-configured with the IP addresses of the media gateways and CSCF  314  used for the emergency calls placed by the unsubscribed communication devices.  
      In accordance with another embodiment of the present invention, the CSCF  314  separately sends the IP address of the media gateway for the emergency call, to the PDG  310 . In accordance with yet another embodiment of the present invention, the emergency call remains routed through the CSCF  314  throughout the duration of the emergency call. In accordance with yet another embodiment of the present invention, if the optional encryption of SIP messages through the CSCF  314  is disabled, then the PDG  310  sniffs the emergency call SIP messages from the CSCF  314  to determine the IP address of the media gateway for the emergency call. The method and system described above allow a user of a communication device, which is not subscribed to the IP based system, to make an emergency call to an emergency call center, without compromising the security of the devices present in the IP based system. Unsubscribed communication devices are not allowed to access resources present in the IP based system, for the purpose of making non-emergency calls.  
      It will be appreciated the communication device  102  and the gateway  306  described herein may be comprised of one or more conventional processors and unique stored program instructions that control the one or more processors to implement, in conjunction with certain non-processor circuits, some, most, or all of the functions of the communication device and the gateway described herein. The non-processor circuits may include, but are not limited to, a radio receiver, a radio transmitter, signal drivers, clock circuits, power source circuits, and user input devices. As such, these functions may be interpreted as steps of a method to perform supporting an emergency call. Alternatively, some or all functions could be implemented by a state machine that has no stored program instructions, or in one or more application specific integrated circuits (ASICs), in which each function or some combinations of certain of the functions are implemented as custom logic. Of course, a combination of the two approaches could be used. Thus, methods and means for these functions have been described herein.  
      It is expected that one of ordinary skill, notwithstanding possibly significant effort and many design choices motivated by, for example, available time, current technology, and economic considerations, when guided by the concepts and principles disclosed herein will be readily capable of generating such software instructions and programs and ICs with minimal experimentation.  
      In the foregoing specification, specific embodiments of the present invention have been described. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of the present invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of present invention. The benefits, advantages, solutions to problems, and any element(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential features or elements of any or all the claims. The present invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims as issued.