Abstract:
An authentication system for performing authentication of a wireless terminal is a system that issues an authentication request to an authentication server connected to a communication network and includes a wireless base station and an authentication server. The wireless base station includes: an authentication information acquisition means for acquiring authentication information from a wireless connection request packet; and an authentication request transmission means for transmitting the authentication information acquired by the authentication information acquisition means and RAS unique information registered in the wireless base station to the authentication server. The authentication server includes a means for acquiring the transmitted authentication information and RAS unique information and comparing the acquired authentication information and RAS unique information with previously registered wireless terminal authentication information previously registered to determine whether or not they coincide with each other. In the case where the acquired authentication information and RAS unique information and previously registered wireless terminal authentication information coincide with each other, the wireless terminal is authenticated.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an authentication system and authentication method for performing authentication of a wireless terminal that issues an authentication request to an authentication server connected to a communication network through a wireless base station and, more particularly, to an authentication system and authentication method in which an authentication server uses an RAS (Remote Access Service) unique information unique to a wireless base station to perform authentication of a wireless terminal. 
     2. Description of the Related Art 
     As a conventional system for performing authentication of a wireless terminal, there is known one in which a wireless terminal issues an authentication request including authentication information such as user ID (identification) and password to a wireless base station, and the wireless base station performs an authentication determination for the received authentication request or asks an authentication server in which authentication information has been registered for the authentication determination to thereby accept or reject an access of the wireless terminal to a network service. 
     As a conventional system for performing authentication of a wireless terminal, a typical authentication system disclosed in Patent Document 1 (JP-2002-324052-A) will be described below with reference to  FIG. 5 . 
     A system for performing authentication of a wireless terminal shown in  FIG. 5  includes a first wireless base station # 1 , a second wireless base station # 2 , a third wireless base station # 3 , a wireless terminal  21 , an authentication server  31 , and a communication network  41 . 
     The first wireless base station # 1  (wireless base station  11 ) includes a wireless interface section  12 , an authentication processing section  14 , a filtering table  15 , a filtering section  16 , and a wired interface section  17 . 
     The second and third wireless base stations # 2  and # 3  have the same configuration as that of the wireless base station  11  and, as shown in  FIG. 5 , a plurality of wireless base stations are connected to the communication network  41 . 
     The wireless base station  11  is connected to the authentication server  31  through the communication network  41 . Upon receiving an authentication request including authentication information such as user ID and password from the wireless terminal  21 , the wireless base station  11  asks the authentication server  31  in which authentication information has been registered for the authentication determination to thereby accept or reject an access of the wireless terminal  21  to a network service. 
     When the wireless terminal  21  is once authenticated by the authentication server  31  and access to a communication network is allowed, the wireless base station  11  stores the terminal ID of the wireless terminal  21  in the filtering table  15 . That is, the acceptance/rejection determination for the wireless terminal  21  to be performed within the wireless base station  11  is made based on whether the terminal ID stored in the filtering table  15  coincides with the received terminal ID. 
     The wireless interface section  12  of the wireless base station  11  performs wireless communication with the wireless terminal  21  to exchange packets therewith. Then, the wireless interface section  12  determines whether a received packet is a wireless connection request packet. If the received packet is the wireless connection request packet, the wireless interface section  12  extracts authentication information and terminal ID from the received wireless connection request packet. If the received packet is not the wireless connection request packet, the wireless interface section  12  extracts terminal ID from the received packet. 
     If a received packet is a wireless connection request packet, the authentication processing section  14  acquires authentication information and terminal ID from the wireless interface section  12 , generates an authentication request packet including the received authentication information, and transmits the generated authentication request packet to the authentication server  31  through the wired interface section  17  and communication network  41 . 
     The authentication processing section  14  receives an authentication reply from the authentication server  31  through the communication network  41  and wired interface section  17 . If the authentication reply indicates “authentication acceptance”, the authentication processing section  14  stores the terminal ID in the filtering table  15  and transmits a wireless connection acceptance packet to the wireless terminal  21 . If the authentication reply indicates “authentication rejection”, the authentication processing section  14  does not store the terminal ID in the filtering table  15  but transmits a wireless connection rejection packet to the wireless terminal  21 . 
     The outline of operation of the entire wireless terminal authentication system shown in  FIG. 5  will next be described. 
     First, the wireless terminal  21  issues a network connection request to the authentication server  31  connected to the communication network  41  through the wireless base station  11 . 
     In this case, the wireless base station  11  acquires authentication information and terminal ID from a wireless connection request packet including the authentication information which is transmitted from the wireless terminal  21  and transmits the acquired information in the form of an authentication request packet to the authentication server  31 . 
     After acquiring the authentication information from the authentication request packet transmitted from the wireless base station  11 , the authentication server  31  checks authentication information that has previously been registered in an authentication information management table  32  provided in the authentication server  31  to determine where there is authentication information coinciding with the acquired authentication information. 
     If there is no authentication information coinciding with the acquired authentication information in the authentication information management table  32  of the authentication server  31 , the authentication server  31  determines “authentication rejection” for the wireless terminal  21 . On the other hand, if there is authentication information coinciding with the acquired authentication information, the authentication server  31  determines “authentication acceptance”. 
     If it is determined to be “authentication acceptance”, the authentication server  31  generates an authentication acceptance reply packet and transmits the generated authentication acceptance reply packet to the wireless base station  11 . On the other hand, if it is determined to be “authentication acceptance”, the authentication server  31  generates an authentication rejection reply packet and transmits the generated authentication rejection reply packet to the wireless base station  11 . 
     If the wireless base station  11  receives the authentication acceptance reply packet, it transmits a wireless connection acceptance replay packet to the wireless terminal  21 . On the other hand, if the wireless base station  11  receives the authentication rejection reply packet, it transmits a wireless connection rejection replay packet to the wireless terminal  21 . 
     As described above, the wireless terminal  21  that has received the wireless connection acceptance packet can be connected to the communication network  41  through the wireless base station  11  and can perform communication with a device connected to the communication network  41 . On the other hand, with regard to the wireless terminal  21  that has transmitted authentication information that does not coincide with the authentication information registered in the authentication information management table  32  of the authentication server  31 , connection to the communication network  41  is rejected for the purpose of preventing unauthorized use of the wireless terminal (see Patent Document 1). 
     In the authentication system disclosed in Patent Document 1, unauthorized use of the wireless terminal can be prevented by deleting the authentication information of the relevant wireless terminal from the authentication information management table  32  of the authentication server  31 , even if a given wireless terminal is stolen or lost. However, in the case where a given wireless terminal is shared by a plurality of users, it is difficult to identify when, where, and by whom the terminal is used. Thus, in the case of theft or loss, it takes a long time to find out the unauthorized use. For this reason, the above authentication system can be said to be vulnerable to the unauthorized use. 
     Here, there is known a method in which authentication information and validity period for authentication are registered in the authentication information table  32  of the authentication server  31  in association with each other. In this method, in the case where the wireless terminal  21  issues a connection request within a given authentication validity period and authentication acceptance is determined, the authentication validity period is updated for prolonged use. 
     In the case where there is no connection request from the wireless terminal  21  within the validity period and authentication acceptance is not determined, expiration of the validity period of the authentication is determined to invalidate the authentication information of the wireless terminal  21 . As described above, by setting time limit for authentication and combining of determinations whether or not the received authentication information and registered authentication information coincide with each other and whether or not the validity period has elapsed, unauthorized access to the communication network  41  can be prevented. 
     To shorten the validity time in such a conventional technique is an effective way for preventing unauthorized use of the wireless terminal at the time of its theft or loss. However, expiration of the authentication validity period may occur frequently due to reasons other than the theft or loss. Accordingly, invalidation work of the authentication information becomes an everyday affair to increase the workload of an administrator who manages the authentication information. Further, the wireless terminal frequently becomes disabled due to the invalidation, interfering with everyday activities. As described above, the abovementioned conventional authentication system is an impractical one. 
     As another system for preventing unauthorized use of the wireless terminal, there are known a security system for a mobile wireless terminal, a mobile wireless terminal, and a recording medium storing a security program (see Patent Document 2 (JP-2001-346257-A)). 
     However, the authentication method for a wireless terminal, wireless base station, and communication system disclosed in Patent Document 1 employs an authentication system obtained by combining authentication information and terminal ID, so that if the wireless terminal is stolen, unauthorized use of the wireless terminal cannot be prevented. 
     Further, the security system for a mobile wireless terminal, mobile wireless terminal, and recording medium storing a security program disclosed in Patent Document 2 prevents the unauthorized use by utilizing authentication information associated with wireless terminal unique information and by periodically changing authentication information to be input by a user. However, in the case where program update or data update in a business terminal needs to be performed through a communication network at night in an unmanned manner, authentication information cannot be input due to unmanned operation. 
     Thus, in the conventional wireless terminal authentication system that rejects authentication according to the set validity period or confirms the validity of authentication based on the ID/password input operation of a user, an effective means of preventing unauthorized use of the wireless terminal at the time of its theft or loss and preventing unauthorized use in a wireless terminal for business use allowing unmanned operation has not been established. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the above problems, and an object thereof is to provide an authentication system and authentication method for performing authentication of a wireless terminal that issues an authentication request to an authentication server connected to a communication network through a wireless base station, having a practical and effective function of preventing unauthorized use of the wireless terminal at the time of its theft or loss. 
     According to an aspect of the present invention, there is provided an authentication system for performing authentication of a wireless terminal that issues an authentication request to an authentication server connected to a communication network through a wireless base station for access to the communication network, wherein the wireless base station comprises: an authentication information acquisition means for acquiring authentication information from a wireless connection request packet including the authentication information transmitted from the wireless terminal; and an authentication request transmission means for transmitting the authentication information acquired by the authentication information acquisition means and RAS unique information which is information unique to the wireless base station that has previously been registered in the wireless base station to the authentication server as an authentication request packet, the authentication server comprises: a base station information acquisition means for acquiring the authentication information and RAS unique information of the wireless base station from the authentication request packet transmitted by the authentication request transmission means; and a base station information determination means for comparing the authentication information and RAS unique information acquired by the base station information acquisition means with wireless terminal authentication information in which the authentication information and RAS unique information have previously been registered in association with each other to determine whether or not they coincide with each other, and in the case where the acquired authentication information and RAS unique information and previously registered wireless terminal authentication information coincide with each other, the base station information determination means authenticates the wireless terminal. 
     In the authentication system according to the present invention, the authentication server may further comprise: a RAS unique information determination means and an authentication result transmission means. The RAS unique information determination means determines authentication rejection in the case where the authentication information acquired by the base station information acquisition means and previously registered wireless terminal authentication information do not coincide with each other; the RAS unique information determination means determines authentication acceptance in the case where the authentication information acquired by the base station information acquisition means and previously registered wireless terminal authentication information coincide with each other and where corresponding RAS information coincide with each other to update the validity period of the wireless terminal authentication information; the RAS unique information determination means determines authentication acceptance in the case where the authentication information acquired by the base station information acquisition means and previously registered wireless terminal authentication information coincide with each other but corresponding RAS information do not coincide with each other and where the authentication request is within the validity period of the wireless terminal authentication information; and the RAS unique information determination means determines authentication rejection in the case where the authentication information acquired by the base station information acquisition means and previously registered wireless terminal authentication information coincide with each other but corresponding RAS information do not coincide with each other and where the authentication request is beyond the validity period of the wireless terminal authentication information. The authentication result transmission means transmits an authentication acceptance replay packet generated by the authentication server to the wireless base station in the case where authentication acceptance is determined by the RAS unique information determination means; and the authentication result transmission means transmits an authentication rejection replay packet generated by the authentication server to the wireless base station in the case where authentication rejection is determined by the RAS unique information determination means. Further, in the authentication system according to the present invention, the wireless base station may further comprise an authentication result base station transmission means. The authentication result base station transmission means transmits a wireless connection acceptance replay packet to the wireless terminal when receiving the authentication acceptance replay packet transmitted by the authentication result transmission means of the authentication server; and the authentication result base station transmission means transmits a wireless connection rejection replay packet to the wireless terminal when receiving the authentication rejection replay packet transmitted by the authentication result transmission means of the authentication server. 
     Further, in the authentication system according to the present invention, in the case where the RAS unique information determination means determines that the RAS unique information coincide with each other and that the authentication request from the wireless base station is beyond the validity period of the wireless terminal authentication information, the authentication server may determine expiration of the authentication validity period and generates an authentication validity period expiration replay packet so as to transmit to the wireless base station. 
     Further, in the authentication system according to the present invention, in the case where the RAS unique information determination means determines that the RAS unique information do coincide with each other, the authentication server may determine authentication rejection regardless of whether the authentication request is within or beyond the validity period. 
     Further, in the authentication system according to the present invention, the authentication server may change the RAS unique information of the wireless base station which has previously been registered in association with the authentication information of the wireless terminal to which the authentication result base station transmission means of the wireless base station has transmitted the wireless connection acceptance replay packet. 
     As described above, according to the present invention, acceptance or rejection of authentication is determined by the authentication information of the wireless terminal and RAS unique information of the wireless base station. Thus, authentication is not accepted by the authentication server unless an authentication request is made through a particular wireless base station, thereby preventing a stolen wireless terminal from illegally accessing the communication network. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a view showing an outline of a wireless terminal authentication system according to a first embodiment of the present invention; 
         FIG. 2  is a flowchart showing operation according to the first embodiment of the present invention; 
         FIG. 3  is a flowchart showing operation according to the first embodiment of the present invention; 
         FIG. 4  is an example of an authentication information management table according to the first embodiment of the present invention; and 
         FIG. 5  is a view showing a typical configuration of a conventional wireless terminal authentication system. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
     First Embodiment 
       FIG. 1  is a view showing an outline of an authentication system for performing authentication of a wireless terminal according to the present invention. In  FIG. 1 , the same parts as those in  FIG. 5  are indicated by the same reference numerals. 
     The authentication system for performing authentication of an wireless terminal shown in  FIG. 1  includes a first wireless base station # 1 , a second wireless base station # 2 , a third wireless base station # 3 , a wireless terminal  21 , an authentication server  31 , and a communication network  41 . 
     The first wireless base station # 1  (wireless base station  11 ) includes a wireless interface section  12 , an RAS (Remote Access Service) unique information management section  13 , an authentication processing section  14 , a filtering table  15 , a filtering section  16 , and a wired interface section  17 . 
     As can be seen from comparison with the abovementioned prior art, the authentication system according to the present embodiments is characterized by further comprising the RAS unique information management section  13 . 
     The second and third wireless base stations # 2  and # 3  have the same configuration as that of the wireless base station  11  and, as shown in  FIG. 1 , a plurality of wireless base stations are connected to the communication network  41 . 
     The wireless base station  11  is connected to the authentication server  31  through the communication network  41 . Upon receiving an authentication request including authentication information such as user ID (identification) and password from the wireless terminal  21 , the wireless base station  11  asks the authentication server  31  in which authentication information has been registered for the authentication determination to thereby accept or reject an access of the wireless terminal  21  to a network service. 
     When the wireless terminal  21  is once authenticated by the authentication server  31  and access to a communication network is allowed, the wireless base station  11  stores the terminal ID of the wireless terminal  21  in the filtering table  15 . In the future authentication process, the filtering section  16  compares received terminal ID and terminal ID stored in the filtering table  15  to perform acceptance/rejection determination for the same wireless terminal  21 . 
     The wireless interface section  12  of the wireless base station  11  performs wireless communication with the wireless terminal  21  to exchange packets therewith. Then, the wireless interface section  12  determines whether a received packet is a wireless connection request packet. If the received packet is the wireless connection request packet, the wireless interface section  12  extracts authentication information and terminal ID from the received wireless connection request packet. If the received packet is not the wireless connection request packet, the wireless interface section  12  extracts terminal ID from the received packet. 
     The RAS unique information management section  13  retains and manages unique information that the wireless base station  11  has. This unique information is RAS unique information. More specifically, MAC (Media Access Control) address, serial number, host name (computer name), and the like correspond to the RAS unique information. 
     If a received packet is a wireless connection request packet, the authentication processing section  14  acquires authentication information and terminal ID from the wireless interface section  12 , generates an authentication request packet including the received authentication information and RAS unique information, and transmits the generated authentication request packet to the authentication server  31  through the wired interface section  17  and communication network  41 . 
     The authentication processing section  14  receives an authentication reply from the authentication server  31  through the communication network  41  and wired interface section  17 . If the authentication reply indicates “authentication acceptance”, the authentication processing section  14  stores the terminal ID in the filtering table  15  and transmits a wireless connection acceptance packet to the wireless terminal  21 . If the authentication reply indicates “authentication rejection”, the authentication processing section  14  does not store the terminal ID in the filtering table  15  but transmits a wireless connection rejection packet to the wireless terminal  21 . 
     When receiving a communication packet of the wireless terminal  21  from the wireless interface section  12 , the filtering section  16  detects a transmission source terminal ID and compares the detected terminal ID and terminal ID stored in the filtering table  15 . If the same terminal ID as the detected terminal ID is stored in the filtering table  15 , the filtering section  16  transfers the communication packet to the communication network  41 . 
     On the other hand, if the same terminal ID as the detected terminal ID is not stored in the filtering table  15 , the filtering section  16  discards the communication packet. 
     Further, the filtering section  16  detects a transmission destination terminal ID from a packet on the communication network  41  and compares the detected transmission destination ID and terminal ID stored in the filtering table  15 . If the same terminal ID as the detected transmission destination terminal ID is stored in the filtering table  15 , the filtering section  16  transfers the communication packet to the wireless interface section  12 . On the other hand, if the same terminal ID as the detected transmission destination terminal ID is not stored in the filtering table  15 , the filtering section  16  does not transfer the packet to the wireless interface section  12 . 
     An example of operation of the authentication system according to the present invention will be described in detail with reference to flowcharts shown in  FIGS. 2 and 3  and an authentication information management table  32  shown in  FIG. 4 . 
     When connecting to the wireless base station  11 , the wireless terminal  21  transmits a wireless connection request packet (corresponding to the abovementioned authentication request) including authentication information. 
     The wireless base station  11  receives the wireless connection request packet in the wireless interface section  12  and acquires authentication information (user ID and password) in the authentication processing section  14  ( 101  of  FIG. 2 ). 
     The authentication processing section  14  acquires the RAS unique information of the wireless base station  11  from the RAS unique information management section  13  and adds it to the authentication information to generate an authentication request packet. Then, the authentication processing section  14  transmits the generated authentication request packet to the authentication server  31  through the wired interface section  17  and communication network  14  ( 102  of  FIG. 2 ). 
     The authentication server  31  acquires the authentication information (user ID, password) of the wireless terminal  21  and RAS unique information of the wireless base station  11  from the authentication request packet ( 103  of  FIG. 2 ) and checks the authentication information management table  32  shown in  FIG. 4  for whether or not there is an user ID coinciding with the user ID of the wireless terminal  21  ( 104  of  FIG. 2 ). 
     The authentication information management table  32  shown in  FIG. 4  is registered in the authentication server  31  and stores user IDs and passwords of respective wireless terminals, RAS unique information in which the respective wireless terminals are registered, and validity periods. Note that the user ID, password, RAS unique information and validity period are merely exemplars, and the content thereof is not limited to the above. 
     If there is no user ID coinciding with the user ID of the wireless terminal  21  in the authentication server  31 , the authentication server  31  determines “authentication rejection”. Then, the authentication server  31  generates an authentication reject replay packet and transmits it to the wireless base station  11  ( 110  of  FIG. 3 ). 
     On the other hand, if there exists a user ID coinciding with the user ID of the wireless terminal  21  in the authentication server  31 , the authentication server  31  determines whether or not the corresponding passwords coincide with each other ( 105  of  FIG. 2 ). 
     If the corresponding passwords do not coincide with each other, the authentication server  31  determines “authentication rejection”. Then, the authentication server  31  generates an authentication reject replay packet and transmits it to the wireless base station  11  ( 110  of  FIG. 3 ). 
     On the other hand, if the corresponding passwords coincide with each other, the authentication server  31  determines whether or not the corresponding RAS unique information of the wireless base station  11  coincide with each other ( 106  of  FIG. 3 ). 
     If the corresponding RAS unique information do not coincide with each other, the authentication server  31  determines whether or not the authentication request is within its validity period ( 109  of  FIG. 3 ). 
     If the authentication information of the wireless terminal  21  is beyond its validity period, the authentication server  31  determines “authentication rejection”. Then, the authentication server  31  generates an authentication rejection replay packet and transmits it to the wireless base station  11  ( 110  of  FIG. 3 ). 
     On the other hand, if the authentication information of the wireless terminal  21  is within its validity period, the authentication server  31  determines “authentication acceptance”. Then, the authentication server  31  generates an authentication acceptance replay packet and transmits it to the wireless base station  11  ( 108  of  FIG. 3 ). 
     If the corresponding RAS unique information coincide with each other, the authentication server  31  determines “authentication acceptance”. Then, the authentication server  31  updates the validity time ( 107  of  FIG. 3 ), generates an authentication acceptance replay packet, and transmits it to the wireless base station  11  ( 108  of  FIG. 3 ). 
     The length of the validity period may be arbitrarily set in the authentication server  31 . For example, the validity period may start from the day on which “authentication acceptance” is determined until six months have elapsed, or to the last day of each quarterly period. 
     In the case where the wireless base station  11  receives the authentication rejection reply packet from the authentication server  31 , it generates a wireless connection rejection packet in the authentication processing section  14  and transmits the generated wireless connection rejection packet from the wireless interface section  12  to the wireless terminal  21 . 
     On the other hand, in the case where the wireless base station  11  receives the authentication acceptance reply packet from the authentication server  31 , it generates a wireless connection acceptance packet in the authentication processing section  14  and transmits the generated wireless connection acceptance packet from the wireless interface section  12  to the wireless terminal  21  and, at the same time, registers the terminal ID of the wireless terminal  21  in the filtering table  15  so as to allow communication between the wireless terminal  21  and communication network  41  during a time period during which the terminal ID is registered. 
     As described above, in the present embodiment, the authentication server  31  stores the authentication information (user ID, password) of the wireless terminal  21  as listed in the authentication information management table  32  of  FIG. 4  and RAS unique information if the wireless base station  11  registers the terminal ID of the wireless terminal  21  that has received the authentication acceptance replay packet from the authentication server  31  in the filtering table  15 . 
     As described above, according to the present embodiment, acceptance or rejection of authentication in the authentication system is determined by the authentication information (user ID, password) of the wireless terminal  21 , RAS unique information of the wireless base station  11 , and validity period of the authentication information. In order to access the communication network  41  once again using the wireless terminal  21  after the validity period has elapsed, it is only necessary to issue authentication request through a particular wireless base station having the same RAS unique information as that has been registered in the authentication server  31 . 
     Thus, even after the validity period has elapsed, it is possible to update the validity period when the RAS unique information registered in the authentication server  31  and RAS unique information of the wireless base station  11  coincide with each other, thereby eliminating the need for an administrator to manage the validity period of authentication information. This leads to a reduction of a workload on the administrator, resulting in a reduction of management cost. 
     Further, by installing the particular wireless base station  11  in an improved security environment, it is possible to prevent a stolen wireless terminal from illegally accessing the communication network after the validity period has elapsed. 
     Another Embodiment 
     In the first embodiment of the present invention, as shown in the flowchart of  FIG. 4 , the authentication server  31  compares the RAS unique information stored in the authentication information management table  32  and RAS unique information received from the wireless base station  11  through the communication network  41  and determines the validity period of the authentication information of the wireless terminal  21  in the case where a result of the comparison between the RAS unique information does not show coincidence. Alternatively, however, the authentication server  31  may determine the update of the validity period of the authentication information in the case where the RAS unique comparison result does not show coincidence, or authentication server  31  may transmit the authentication rejection replay in the case where the RAS unique comparison result does not show coincidence. 
     In this case, the authentication server  31  can identify the wireless terminal  21  and wireless base station  11  by confirming the coincidence between the RAS unique information. Therefore, the authentication server  31  can determine the update of the validity. 
     Further, in the case where the wireless terminal  21  is used in factories or research facilities, the wireless base station  11  can be identified. Thus, if a result of the comparison between the RAS unique information does not show coincidence, the authentication server  31  can determine that the wireless terminal  21  has been illegally used due to theft or loss to determine “authentication rejection” for the wireless terminal  21 . 
     Further, the authentication server  31  may not only update the validity period in the authentication management table  32  but also change the RAS unique information registered therein. 
     Specifically, in the case where the wireless terminal  21  goes out of the coverage of the wireless base station  11  due to removal or job transfer of a user of the terminal  21 , the authentication server  31  changes the RAS unique information of the authentication information management table  32  to RAS unique information of a new wireless base station  11  that covers the wireless terminal  21  only for the wireless terminal  21  to which the authentication server  31  has issued the authentication acceptance reply through the previous wireless base station  11 . As a result, the user can use the wireless terminal  21  to access the communication network through a new wireless base station  11  performing troublesome operations. 
     Alternatively, the authentication server  31  may change the RAS unique information of the authentication information management table  32  for the purpose of canceling prevention of unauthorized use due to theft or loss of the wireless terminal  21 . 
     Specifically, for example, in the case where the stolen or lost wireless terminal  21  issues an authentication request from a wireless base station  11  covering the area other than that associated with the wireless terminal  21 , the authentication request is rejected by the authentication server for prevention of unauthorized use. 
     However, in the case where the wireless terminal  21  is stolen or lost and the identity of the user has been confirmed afterwards, the RAS unique information of the authentication information table  32  of the authentication server  31  may be changed so as to cancel a function of preventing unauthorized use of the wireless terminal  21  found after its theft or less. 
     Further, by setting new RAS unique information without changing the authentication information of the wireless terminal  21 , it is possible to change the wireless base station  11  covering the wireless terminal  21  while maintaining the existing authentication information of the wireless terminal  21 , thereby improving the prevention function against the unauthorized use due to the theft or loss.