BACKGROUND OF THE INVENTION  
         [0001]    1. Field of Invention  
           [0002]    The invention relates to a public network and, in particular, to an authentication system and method for public services on a wireless local area network (WLAN).  
           [0003]    2. Related Art  
           [0004]    Since the introduction of the global system for mobile communication (GSM), wireless communications have had a great breakthrough in security. This breakthrough came from the idea of installing a subscriber identity module (SIM) on the mobile phone, helping the mobile network in authentication and encryption. FIG. 1 shows a structure of the GSM authentication system in the prior art. The mobile phone  100  has an SIM card  88  for performing authentication with the GSM network. In the GSM network, the base station (BS)  36  exchanges wireless signals with the mobile phone  100  and wired signals with the mobile switch center (MSC)  70 . The MSC  70  and the visitor location register (VLR)  75  have mission of performing an authentication procedure for the mobile phone  100 . (Therefore, the MSC  70  and the VLR  75  are usually designed to be together.) Every time a mobile phone  100  requests services, the VLR  75  asks the MSC  70  to authenticate the mobile phone  100 . The MSC  70  sends out an authentication request to and receives an authentication response from the mobile phone  100 , checking whether the authentication response from the mobile phone  100  is correct. If the authentication is successful, the MSC  70  notifies the mobile  100  of services accept; otherwise, the MSC  70  notifies the mobile  100  of services reject. In other elements of the GSM network, the authentication center (AuC)  95  keeps authentication keys Ki of mobile phones  100 , generates authentication parameters (e.g. RAND, SRES, and so on), and sends them to the VLR  75  through the home location register (HLR)  90 . The billing center (BC)  80  accepts charging data records (CDR&#39;s)  86  generated by the MSC  70  for billing information.  
           [0005]    In recent years, the WLAN has been used to provide public services due to its tremendous growth. When the public uses WLAN cards to access the Internet services through the public WLAN set up by a service provider, security becomes the most important issue. Therefore, most famous manufacturers install SIM cards in their WLAN card products to enhance the WLAN security. FIG. 2 shows a structure of the public WLAN authentication system in the prior art. The structure contains four types of elements: client end, access network end, Internet end, and GSM core network end. The user end includes a mobile station (MS)  10  and a WLAN card  200 , where the WLAN card  200  is equipped with an SIM card  88 . The access network end includes a WLAN access point (AP)  30 , a router  40 , and an authentication gateway (AG)  250 . The Internet end contains the Internet  50  and a server  60 . The GSM core network end includes a MSC  70 , a VLR  75 , an AuC  95 , an HLR  90 , and a BC  80  (just as in FIG. 1). In the structure shown in FIG. 2, if the MS  10  passes authentication, it then has access rights to the AP  30  and the router  40 , connecting to the Internet  50  and obtaining the Internet services from the server  60 . During the authentication process, when the MS  10  requires Internet services, it sends out a service request to the AG  250 . The AG  250  transfers this service request to the VLR  75 . The VLR  75  then asks the MSC  70  to send out an authentication request to the MS  10 . This authentication request is transferred by the VLR  75  to the MS  10 . The MS  10  uses the SIM card  88  of the WLAN card  200  to execute an authentication response. The authentication response is transferred by the AG  250  to the MSC  70 , checking if the authentication is successful. If the authentication is successful, the MSC  70  notifies the AG  250  of services accept and the AG  250  allows the MS  10  to connect to the Internet  50  using the AP  30  and the router  40 . If the authentication fails, the MSC  70  notifies the AG  250  of service reject. After the MS  10  passes the authentication, the router  40  generates a usage record. The AG  250  generates the charging data record according to such usage records and sends the charging data record to the BC  80 . Therefore, the main task of the AG is to process the service request from the MS, to transfer the authentication signals between the MS and the MSC, to control the access right of the MS to the Internet, and to generate CDR&#39;s for the BC.  
           [0006]    Due to the SIM card  88  embedded inside the WLAN card  200 , the design of the WLAN card becomes much more complicated. Consequently, some companies choose to leave the current WLAN card design unchanged but add the SIM card function to the MS. As shown in FIG. 3, the MS  10  is equipped with a WLAN card  20 . It reads the data on the SIM card  88  through a computer interface  300  (e.g. PCMCIA, USB, RS232, etc) to perform authentication. (The network end in FIG. 3 is totally the same as that in FIG. 2.)  
           [0007]    From FIGS.  1  to  3 , it is obvious that the SIM card  88  is embedded in the client end devices, such as the mobile phone  100  in FIG. 1, the WLAN card  200  in FIG. 2, and the laptop computer MS  10  in FIG. 3. In these authentication systems, the client end devices use the SIM card to obtain authentication from an authentication server. However, this requires design of an SIM card slot in the client end device, which unavoidably increases the complexity and cost in design.  
         SUMMARY OF THE INVENTION  
         [0008]    To avoid changes in the design of the client end devices, to lower the client end device cost, and to achieve the objective of public wireless network authentication, the invention provides an authentication system and method for public wireless networks. The system includes an MS, an authentication server, and an authentication agent (AA). The MS no longer has an SIM card installed. The SIM card of the MS is installed on the AA. So the MS performs authentication with the AA, while the AA perform authentication with the authentication server. In addition, the AA has to process the service request from the MS, control the access right of the MS to the Internet, and generate CDR&#39;s for the BC. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]    These and other features, aspects and advantages of the invention will become apparent by reference to the following description and accompanying drawings which are given by way of illustration only, and thus are not limitative of the invention, and wherein:  
         [0010]    [0010]FIG. 1 is a structural diagram of the GSM authentication system in the prior art;  
         [0011]    [0011]FIG. 2 is a structural diagram of the public WLAN authentication system in the prior art;  
         [0012]    [0012]FIG. 3 is a structural diagram of the public WLAN authentication system in the prior art;  
         [0013]    [0013]FIG. 4 is a structural diagram of the disclosed public WLAN authentication system according to the present invention;  
         [0014]    [0014]FIG. 5 is a signaling flow chart of a normal MS in the authentication system according to the present invention; and  
         [0015]    [0015]FIG. 6 is a signaling flow chart of a roaming MS in the authentication system according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0016]    With reference to FIG. 4, the disclosed public WLAN authentication system comprises five types of elements: client end elements, access network end elements, external access network end elements, Internet end elements, and GSM core network end elements. The client end elements include an MS  10  and a WLAN card  20 . The access network end elements include an AP  30 , a router, and an AA  800  in a WLAN. The AA  800  is connected to an SIM card slot  888  through a computer interface  886 . The SIM card slot  888  has an SIM card  88 . The computer interface  886  may be an RS232, USB, PCI or PCMCIA bus so that the AA  800  can access the authentication information on the SIM card  88 . The external access network end elements include a BS  35 , a router  45 , and an access right controller (ARC)  600 . The Internet end elements include the Internet  50  and a server  60 . The GSM core network end elements include an MSC  70 , a VLR  75 , an AuC  95 , an HLR  90 , and a BC  80 . (The GSM core network end elements are the same as those in FIG. 1.)  
         [0017]    In the structure of FIG. 4, when the MS  10  asks for the Internet services, the MS  10  has to authenticate with the AA  800  and the AA  800  authenticates with the MSC  70  using the SIM card  88  of the MS  10 . The authentication communication protocol between the MS  10  and the AA  800  needs not be standard. It can be the remote authentication user service (RADIUS), Kerberos, or the service provider&#39;s property. If the MS  10  fails the authentication, the service request is rejected. If the MS  10  passes the authentication, it gains the access right to the BS  30  and the router  40  and is therefore able to obtain the Internet services from the server  60  and connect to the Internet  50 . After the MS  10  obtains the Internet services, the router  40  generates a usage record. The AA  800  then produces CDR&#39;s according to such usage records for the BC  80 .  
         [0018]    With reference to FIG. 5, the disclosed authentication system comprises three authentication elements: an MS  10 , an AA  800 , and an authentication server  700 . The AA  800  has the SIM card  88  of the MS  10 , to process authentication with the authentication server  700  on behalf of the MS  10 . The authentication server  700  can be the MSC  70  in a GSM network, responsible for the authentication with the SIM card  88 . When the MS  10  needs Internet services, it sends out a service request to the AA  800  (signal  510 ) and processes authentication with the AA  800  (signal  520 ). If the MS  10  fails the authentication, the service request is rejected. If the authentication is successful, the AA  800  sends out a service request to the authentication server  700  (signal  530 ). The authentication server  700  sends out an authentication request (signal  540 ) to the AA  800 . The AA  800  uses the SIM card  88  of the MS  10  to process authentication response (signal  550 ). When the authentication server  700  receives the authentication response  550 , it checks whether the authentication is successful. If the authentication is successful, the authentication server  700  notifies the AA  800  of the services accept (signal  560 ). The AA  800  then notifies the MS  10  of the services accept (signal  570 ). The AA  800  further allows the MS  10  to connect to the Internet. If the authentication fails, the authentication server  700  notifies the AA  800  of the services reject (signal  580 ). The AA  800  then notifies the MS  10  of the services reject (signal  590 ).  
         [0019]    Therefore, the AA in the disclosed authentication system has the SIM card of the MS. Its tasks include processing the service requests of the MS, processing authentication with the MS, processing authentication with the authentication server (e.g. the MSC), controlling the access right of the MS to the Internet, and generating CDR&#39;s for the BC.  
         [0020]    In the structure shown in FIG. 4, the MS  10  may roam to an external access network. If the MS  10  now needs Internet services, it has to obtain the access right for the AP  35  and the router  45 . In the external access network, the access right of the AP  35  and the router  45  is monitored by the ARC  600 . Therefore, the MS  10  has to send out a service request to the ARC  600  until it obtains services accept from the ARC  600 .  
         [0021]    With reference to FIG. 6, the authentication system for a roaming MS comprises four authentication elements: an MS  10 , an ARC  600 , an AA  800 , and an authentication server  700 . When the MS  10  roams to the external access network and needs the Internet services, the MS  10  sends out a service request (signal  610 ) to the ARC  600 . The ARC  600  in turn sends out a service request (signal  615 ) to the AA  800  of the MS  10 . The AA  800  starts to process authentication for the MS  10 . If the authentication fails, the service request is rejected. If the authentication is successful, the AA  800  processes authentication with the authentication server  700  (signals  530 - 580  as in FIG. 5). If the authentication is also successful, then the AA  800  notifies the ARC  600  that the service request is accepted (signal  660 ). The ARC  600  further notifies the MS  10  about services accept (signal  665 ) and allows the MS  10  to connect to the Internet. On the other hand, if the last authentication fails, the AA  800  notifies the ARC  600  of services reject (signal  680 ), and the ARC  600  notifies the MS  10  of services reject (signal  685 ).  
         [0022]    Although the invention has been described with reference to specific embodiments, this description is not meant to be construed in a limiting sense. Although the embodiments explicitly refer to the public WLAN, the invention can still be applied to public wired networks. Various modifications of the disclosed embodiments, as well as alternative embodiments, will be apparent to persons skilled in the art. It is, therefore, contemplated that the appended claims will cover all modifications that fall within the true scope of the invention.  
         [0023]    Furthermore, the public authentication system of the invention does not install a SIM card on the MS. Instead, a SIM card is installed in the AA so that one does not need to change the design of the user&#39;s MS and the manufacturing cost lowers. By processing authentication between the MS and the AA and between the AA and the authentication server using the SIM card of the MS, the invention also achieve the same objective of authentication between the MS and the authentication server.  
         [0024]    While the invention has been described by way of example and in terms of the preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements as would be apparent to those skilled in the art. Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.
In conventional public networks, a subscriber identity module (SIM) is installed on a mobile station for authenticating users and improving the communication security between mobile stations and the network. This specification proposes an authentication agent (AA) installed on a network and with the SIM of the mobile station installed on the AA. Thus, the mobile station gets authenticated from the AA and then the AA uses the SIM of the mobile station to obtain authentication from the authentication server.