Abstract:
Provided is a method for enabling a first communications system for providing first communication services to cooperate with a second communications system for providing second communication services for providing complementary communication services in a network including the first and second communications system, which includes the steps of detecting the necessity of providing the second communication services for a mobile communication terminal presently receiving the first communication services; and notifying the second communications system of the necessity of providing the second communication services so as to cause the second communications system to establish a communication link for the mobile communication terminal to receive the second communication services.

Description:
PRIORITY  
       [0001]     This application claims priority under 35 U.S.C. §119 to an application entitled “Method for Service Interworking Between Heterogeneous Systems” filed in the Korean Intellectual Property Office on May 30, 2005 and assigned Serial No. 2005-45651, the contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates generally to a communication system, and more particularly to a system for enabling heterogeneous communication systems to cooperate in providing communication services and method therefor.  
         [0004]     2. Description of the Related Art  
         [0005]     Presently communication systems are undergoing rapid development toward next generation communication systems employing new communication technologies. Accordingly, provision of communication services requires using the next generation communication systems, rather than the conventional systems. But, until the communication services employing the next generation communication system become more stable and marketable, employing both the next generation communication system and the conventional communication system remains essential for complementary communication services.  
         [0006]     For example, if the conventional communication system is based on Code Division Multiple Access 2000 1×EVDO (CDMA 2000 1× Evolution Data Only), and the next generation communication system is based on broadband wireless access (BWA), it is necessary to employ both CDMA 2000 1×EVDO system and BWA system for providing complementary communication services until BWA becomes more stable and marketable. This calls for a technological solution for enabling the conventional communication system and the next generation communication systems to cooperate for providing complementary communication services.  
       SUMMARY OF THE INVENTION  
       [0007]     It is an object of the present invention to provide a system and method for enabling heterogeneous communication systems to cooperate for providing complementary communication services.  
         [0008]     According to an aspect of the present invention, a method for enabling a first communication system for providing first communication services to cooperate with a second communication system for providing second communication services in providing complementary communication services in a network including the first and second communication system, includes detecting the necessity of providing the second communication services for a mobile communication terminal presently receiving the first communication services; and notifying the second communication system of the necessity of providing the second communication services for causing the second communication system to establish a communication link for the mobile communication terminal to receive the second communication services.  
         [0009]     According to still another aspect of the present invention, a method for enabling heterogeneous communication systems to cooperate for providing communication services, includes detecting the necessity of providing second communication services for a mobile communication terminal receiving first communication services from a first communication system through a first communication link; causing the first communication system to ask a second communication system for authentication of the mobile communication terminal; causing the second communication system to notify the first communication system of permission for providing second communication services after authenticating the mobile communication terminal; causing the first communication system to notify the mobile communication terminal of the permission for the second communication system to provide the second communication services; and causing the mobile communication terminal to establish a second communication link with the second communication system to provide the second communication services for the terminal.  
         [0010]     According to still yet another aspect of the present invention, a system for enabling heterogeneous communication systems to cooperate for providing complementary communication services, includes a mobile communication terminal capable of working both at first communication service mode and second communication service mode; a first communication system for providing first communication services; and a second communication system for providing first communication services, wherein the first communication system detects the necessity for providing the second communication services for the mobile communication terminal presently receiving the first communication services, and notifies the second communication system of the necessity of providing the second communication services so as to cause the second communication system to establish a communication link for the mobile communication terminal to receive the second communication services. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawing in which:  
         [0012]      FIG. 1  is a block diagram schematically illustrating a network designed to enable CDMA 2000 1×EVDO and BWA systems to cooperate in providing complementary communication services according to the present invention;  
         [0013]      FIG. 2  is a block diagram schematically illustrating the internal structure of CAG ( 117 ) as shown in  FIG. 1 ;  
         [0014]      FIG. 3  is a flowchart for illustrating a process of a dual mode communication terminal for accessing a network as shown in  FIG. 1  according to the present invention; and  
         [0015]      FIG. 4  is a schematic diagram for illustrating the process of providing BWA communication services to a dual mode communication terminal connected to CDMA 2000 1×EVDO communication system according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0016]     Preferred embodiments of the present invention will be described herein below with reference to the accompanying drawings. In the drawings, the same or similar elements are denoted by the same reference numerals even though they are depicted in different drawings. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.  
         [0017]     In order to more specifically describe the inventive system and method for enabling heterogeneous communication systems to cooperate for providing complementary communication services for a mobile communication terminal, the conventional communication system is selected based on Code Division Multiple Access 2000 1×EVDO (CDMA 2000 1×EVDO), and the next generation communication system on Broadband Wireless Access (BWA).  
         [0018]     Referring to  FIG. 1 , there is shown a network designed to enable BWA system  110  and CDMA 2000 1×EVDO system  130  to cooperate in providing complementary communication services according to the present invention. For simplicity, a communication system presently providing communication services for a mobile communication terminal is referred to as “home communication system”, and another communication system where the mobile communication terminal visits as “visit communication system”. In  FIG. 1 , if it is assumed that a mobile communication terminal presently connected to the BWA communication system  110  visits CDMA 2000 1×EVDO system  130 , where the home communication system of the mobile communication terminal will be the BWA communication system  110 , and the visit communication system will be the CDMA 2000 1×EVDO system  130 . In order to receive complementary communication services by the cooperation of the BWA and CDMA 2000 1×EVDO systems  110  and  130 , respectively, the mobile communication terminal can work at dual mode, i.e., both at BWA communication mode and CDMA 2000 1×EVDO communication mode.  
         [0019]     The BWA communication system  110  includes a subscriber station (SS)  111 , a radio access station (RAS)  113 , an access control router (ACR)  115 , a cellular access gateway (CAG)  117 , and an authorization, authentication, and accounting (AAA) server  119 . It is noted that the dual mode terminal as described above herein is named SS  111  when working at the BWA communication mode.  
         [0020]     The ACR  115  performs the authentication of the SS  111 , the treatment of medium access control (MAC) protocol, allocation of Internet protocol (IP) addresses, and the routing function. The CAG  117  performs the authentication of the SS  111  accessing the CDMA 2000 1×EVDO communication system  130 , the treatment of point-to-point protocol (“PPP”) session, allocation of IP addresses, routing, and provision of BWA communication services for the SS  111 . The AAA server  119  performs the authentication, authorization and accounting of the SSS  111 .  
         [0021]     The CDMA 2000 1×EVDO communication system  130  includes an access terminal (AT)  131 , an access network controller/access network transmission system (ANC ANTS)  133 , a packet control function (“PCF”) unit  135  for performing session control/mobility management (SC/MM), a packet data serving node (hereinafter referred to as “PDSN”)  137 , and an access network (AN)-AAA proxy server  139 . In this case, it is noted that the dual mode communication terminal is called AT  131  working at the CDMA 2000 1×EVDO communication mode.  
         [0022]     The PCF (SC/MM) unit  135  manages the packet data session between the ANC/ANTS  133  and the PDSN  137  or the CAG  117 , delivering a user traffic. The PDSN  137  delivers CDMA 2000 1×EVDO communication services to a mobile communication terminal connected to the CDMA 2000 1×EVDO communication system  130 . The AN-AAA proxy server  139  delivers the signaling messages relating to the authentication, authorization and accounting between the AT  131  connected to the CDMA 2000 1×EVDO communication system  130  and the AAA server  119 .  
         [0023]     Hereinafter will be described the cooperation of the BWA and CDMA 2000 1×EVDO communication systems  110  and  130 , respectively, for providing complementary communication services for the mobile communication terminal.  
         [0024]     First, accessing the BWA communication system  110 , the SS  111  may receive BWA communication services through the RAS  113  and ACR  115 .  
         [0025]     Second, accessing the CDMA 2000 1×EVDO communication system  130 , the AT  131  can receive BWA communication services through the CAG  117  connected to the PCF (SC/MM) unit  135  to the ANC/ANTS  133 .  
         [0026]     Third, accessing the BWA communication system  110 , the SS  111  may receive CDMA 2000 1×EVDO communication services through the CAG  117  connected to the ACR  115  to RAS  113 .  
         [0027]     Fourth, accessing the CDMA 2000 1×EVDO communication system  130 , the AT  131  may receive CDMA 2000 1×EVDO communication services through PDSN  137  connected to the PCF (SC/MM) unit to the ANC/ANTS  133 . The following Table 1 shows the interfaces between the units constituting the network shown in  FIG. 1 .  
                   TABLE 1                       Interface   Description                   A8   Treating a user traffic transferred between ANC and           PCF unit       A9   Defining signaling process such as transmission, ending,           and reception of a packet call between ANC and PCF unit       A10   Treating a user traffic transferred between PCF unit           and PDSN or CAG       A11   Defining signaling process such as transmission and           ending of a packet call between PCF unit and PDSN or CAG       A12   Authenticating a user and mobile communication terminal           between SC/MM server and AN-AAA proxy server, and           defining the signaling process for delivering Mobile Node           Identifier (MNID)       H bis     Transferring signaling and a user traffic between ACR           and RAS       H ia     Transferring session information and establishing tunnel           either between different ACRs or between ACR and CAG       IEEE   Defining wireless access specification between the       802.16e   mobile terminal and RAS, and protocol governing the           signaling process, packet transferring process and MAC           relating to authentication and connection of the mobile           terminal accessing a BWA system       IS-856   Defining radio access specification between the mobile           terminal and ANTS, and protocol governing the signaling           process, packet transfer process and MAC relating to           transmission/reception of a CDMA 2000 1 × EVDO           packet call                  
 
         [0028]     In order to enable the BWA and CDMA 2000 1×EVDO communication systems  110  and  130  to cooperate for providing complementary communication services, the dual mode mobile communication terminal and CAG  117  require the following essential functions.  
         [0029]     First, the dual mode terminal requires the particular functions as follows:  
         [0030]     1. To select and access the optimum one of the BWA and CDMA 2000 1×EVDO communication systems;  
         [0031]     2. To generate a network access identifier (NAI) delivered to the PCF (SC/MM) unit  135  during the authentication of challenge handshake authentication protocol (CHAP) upon accessing the CDMA 2000 1×EVDO communication system. In this case, the NAI includes the identifier by which the BWA communication system can identify the dual mode terminal; and  
         [0032]     3. To perform establishment of the PPP session and service authorization with the CAG  117  and receive an allocation of an IP address after transmitting a CDMA 2000 1×EVDO call when the authentication of CHAP is successfully completed by accessing the CDMA 2000 1×EVDO communication system  130 .  
         [0033]     Secondly, the CAG  117  requires the particular functions as follows:  
         [0034]     1. To treat A10/A11 interfaces with the PCF (SC/MM) unit  135 ;  
         [0035]     2. To dynamically generate or maintain security association (SA) with the PCF (SC/MM) unit  135 ;  
         [0036]     3. To generate and maintain the PPP session for the dual mode terminal connected to the CDMA 2000 1×EVDO communication system  130 ;  
         [0037]     4. To perform the service authorization between the AAA server  119  and the dual mode terminal connected to the CDMA 2000 1×EVDO communication system  130 ;  
         [0038]     5. To allocate an IP address for the dual mode terminal accessing the CDMA 2000 1×EVDO communication system  130  according to dynamic host control protocol (DHCP) or IP control protocol (hereinafter referred to as “IPCP”), and then to allocate the static IP address received together with the service authorization result from the AAA server  119  to the dual mode terminal;  
         [0039]     6. To support a communication terminal receiving mobile IP services by including foreign agent (FA) function;  
         [0040]     7. To perform PPP framing delivered through the A10 interface to the PCF(SC/MM) unit  135  for a user traffic transferred to the dual mode terminal connected to the CDMA 2000 1×EVDO communication system  130 ;  
         [0041]     8. To perform IP routing for user traffic received from the PCF (SC/MM) unit  135  through the A10 interface;  
         [0042]     9. To collect the accounting information of the dual mode terminal accessing the CDMA 2000 1×EVDO communication system  130  delivered to the AAA server  119 ; and  
         [0043]     10. To end the PPP session of the dual mode terminal upon requesting of the AAA server  119 .  
         [0044]     Describing the internal structure of the CAG  117  in connection with  FIG. 2 , the CAG  117  generally includes a session management part, an interface processor, a traffic processor, and a network device.  
         [0045]     The session management part includes a BWA session management part  205  for managing the BWA session of the AT  131 , and a PPP management part  213  for managing the PPP session and PPP framing. The session management part manages the session of the mobile communication terminal connected to the BWA or CDMA 2000 1×EVDO communication system  110  or  130  by using the access information of the mobile communication terminal.  
         [0046]     The interface processor includes H in  interface processor  201  for processing the H ia  interface between the ACR  115  and CAG  117 , and A10/A11 interface processor  211  for processing the A10/A11 interface between the CAG  117  and PCF (SC/MM) unit  135 . The H ia  interface processor  201  processes the signaling messages transferred between the ACR  115  and CAG  117 , and the user traffic transferred through a tunnel between the ACR  115  and CAG  117 .  
         [0047]     The traffic processor includes an IP routing management part  203  for managing IP routing, an AAA function processor  207  for processing AAA signaling messages of authentication, authorization and accounting, and a transmission control protocol (TCP)/IP protocol stack  209 .  
         [0048]     The network device  215  transfers the signaling messages received from an external unit like the ACR  115  to the interface processor, and also from the interface processor to an external unit such as the ACR  115 .  
         [0049]     Describing the operation of the CAG  117 , if the dual mode terminal accesses the BWA communication system  110 , the H ia  signaling messages transmitted from the ACR  115  are delivered through the network device  215  and TCP/IP protocol stack  209  to the H ia  interface processor  201 , which processes various signaling messages defined by the H ia  interface. On the contrary, the signaling messages transmitted from the H ia  interface processor  201  of the CAG  117  are delivered through the TCP/IP protocol stack  209  and network device  215  to the ACR  115 .  
         [0050]     Alternatively, if the dual mode terminal accesses the CDMA 2000 1×EVDO communication system  130 , the A11 signaling messages transferred from the PCF (SC/MM) unit  135  are delivered the network device  215  and TCP/IP protocol stack  209  to the A10/A11 interface processor  211 . On the contrary, the A11 signaling messages transmitted from the A10/A11 interface processor  211  of the CAG  117  are delivered through the TCP/IP protocol stack  209  and network device  215  to PCF (SC/MM) unit  135 . In addition, the signaling messages between the CAG  117  and AAA server  119 , for example, those according to the remote authentication dial-in user service (“RADIUS”) protocol and DIAMETER protocol, are delivered through the AAA function processor  207 , TCP/IP protocol stack  209  and network device  215 .  
         [0051]     In addition, if a dual mode terminal connected to the BWA communication system  110  transmits an IP packet, it is delivered through the network device  215  and TCP/IP protocol stack  209  of the CAG  117  to the IP routing management part  203  to another dual mode communication terminal connected to an external communication system different from the BWA communication system connected with the former dual mode communication terminal, for example, the CDMA 2000 1×EVDO communication system  130 , or other dual mode terminals connected to the BWA communication system  110 . The same procedure applies when other dual mode terminals accessing the CDMA 2000 1×EVDO communication system  130  or the BWA communication system  110  transmit an IP packet.  
         [0052]     Alternatively, if the dual mode terminal accessing the CDMA 2000 1×EVDO communication system  130  transmits a PPP frame, it is delivered through the network device  215  and TCP/IP protocol stack  209  of the CAG  117  to the A10/A10 interface processor  211 , which removes the IP header and GRE (Generic Record Encapsulation) header from the PPP frame delivered to the PPP management part  213 , which in turn decodes the PPP frame to generate the IP packet delivered to the IP routing management part  203 . Then the IP routing management part  203  delivers the IP packet through the TCP/IP protocol stack  209  and network device  215  to an external communication system or another dual mode terminal according to the result of a routing procedure for obtaining packet transfer case by referring to a routing table, for example, one prescribed in the system.  
         [0053]     Alternatively, if a dual mode terminal connected to an external communication system or another dual mode terminal connected to the same BWA communication system  110  transmits an IP packet to a dual mode terminal connected to the CDMA 2000 1×EVDO communication system  130 , the IP packet is delivered through the network device  215  and TCP/IP protocol stack  209  of the CAG  117  to the PPP management part  213 , which then transforms the IP packet into a PPP frame delivered to the A10/A11 interface processor  211 . Then the A10/A11 interface processor  211  generates the GRE header for the PPP frame delivered through the TCP/IP protocol stack  209  and network device  215  to the PCF (SC/MM) unit  135 . Thus, the PPP frame is transferred to the dual mode terminal connected to the CDMA 2000 1×EVDO communication system  130 .  
         [0054]     Referring to  FIG. 3 , there is shown the process of a dual mode terminal placed in the service region of the CDMA 2000 1×EVDO communication system  130  to access the system. In this case, the dual mode terminal firstly accesses the CDMA 2000 1×EVDO communication system  130  after power-on, and then the BWA communication system. For convenience&#39;s sake, the service region of the CDMA 2000 1×EVDO communication system  130  is referred to as “CDMA 2000 1×EVDO communication service region”.  
         [0055]     The dual mode terminal placed in the CDMA 2000 1×EVDO communication service region, i.e., AT  310  powered on, searches the CDMA 2000 1×EVDO communication system for the ANC/ANTS to which it belongs.  
         [0056]     Upon detecting the ANC/ANTS, the AT  310  accesses the PCF (SC/MM) unit  330  of the CDMA 2000 1×EVDO communication system through the ANC/ANTS  320 . The AT  310  performs unicast access terminal identifier (“UATI”) allocation and CDMA 2000 1×EVDO session negotiation with the PCF (SC/MM) unit  330  (Step  301 ).  
         [0057]     Completing the UATI allocation and CDMA 2000 1×EVDO session negotiation, the AT  310  originates a CDMA 2000 1×EVDO packet call to receive an allocation of wireless resources from the CDMA 2000 1×EVDO system. Namely, the AT  310  performs AT initiated connection setup with the PCF (SC/MM) unit  330  (Step  303 ). Then, the AT  310  performs link control protocol (LCP) negotiation, i.e., link hierarchical negotiation, according to the PPP protocol, with the PCF (SC/MM) unit  330  (Step  305 ).  
         [0058]     Following the LCP negotiation, the PCF (SC/MM) unit  330  sends a CHAP challenge value to the AT  310 . In this case, the challenge value is a random value generated by the authentication server, used by the authenticated terminal to calculate a response value transmitted to the authentication server (Step  307 ). Meanwhile, the AT  310  generates NAI during the CHAP authentication process, transmitted to the PCF (SC/MM) unit  330 . The NAI generated by the AT  310  represents the identifier for distinguishing the AT  310 .  
         [0059]     Thereafter receiving the CHAP response value from the AT  310 , the PCF (SC/MM) unit  330  generates A12 access request message delivered to the AN-AAA proxy server  340  (Step  309 ). Then the AN-AAA proxy server  340  analyzes the NAI contained in the A12 access request message to obtain the information of the AAA server  360  to allow access of the AT  310 . Thereafter, the AN-AAA proxy server  340  generates an access request message transmitted to the AAA server  360  (Step  311 ).  
         [0060]     Upon receiving the access request message, the AAA server  360  analyzes the information of the NAI, CHAP challenge/response values, etc. contained in the access request message to perform the access authentication. Then completing successfully the access authentication, the AAA server  360  transmits an access accept message in response to the access request message to the AN-AAA proxy server  340  (Step  313 ).  
         [0061]     Receiving the access accept message from the AAA server  360 , the AN-AAA proxy server  340  generates A12 access accept message transmitted to the PCF (SC/MM) unit  330  (Step  315 ), which in turn generates a CHAP success message delivered to the AT  310  (Step  317 ). Namely, the PCF (SC/MM) unit  330  notifies the AT  310  of the successful authentication by the CHAP success message.  
         [0062]     After transmitting the CHAP success message to the AT  310 , the PCF(SC/MM) unit  330  generates A14 authentication completed message transferred to the ANC/ANTS  320  (Step  319 ), which in turn transmits A14 authentication completed acknowledge (ACK) message generated in response to the A14 authentication completed message to the PCF(SC/MM) unit  330  (Step  321 ). In this case, the message generated by the ANC/ANTS  320  in response to the A14 authentication completed message from the PCF(SC/MM) unit  330  may be A14 authentication completed acknowledge (ACK) message or A14 authentication completed negative-acknowledge (NACK) message, whereby the AT  310  is notified whether the access authentication has succeeded or failed.  
         [0063]     Completing the access authentication of the AT  310 , the ANC/ANTS  320  generates A9-setup-A8 message delivered to the PCF (SC/MM) unit  330  to request the setup of a CDMA 2000 1×EVDO packet call (Step  323 ). In this case, the A9-setup-A8 message represents the signaling message to set up A8 interface, i.e., GRE tunnel between the PCF (SC/MM) unit  330  and the ANC/ANTS  320 .  
         [0064]     Upon receiving the A9-setup-A8 message, the PCF (SC/MM) unit  330  generates A11 registration request message delivered to the CAG  350  (Step  325 ). In this case, the A11 registration request message represents the signaling message to set up A10 interface, i.e., GRE tunnel between the PCF (SC/MM) unit  330  and CAG  350 . Upon receiving the All registration request message, the CAG  350  recognizes that the AT  310  is attempting to access the BWA communication system through the CDMA 2000 1×EVDO communication system.  
         [0065]     Then the CAG  350  transmits A11 registration response message generated in response to the A11 registration request message to the PCF (SC/MM) unit  330 . Namely, the CAG  350  allows the setup of GRE, whereby the GRE tunnel is formed between the PCF (SC/MM) unit  330  and the CAG  350  (Step  327 ).  
         [0066]     Following setting up the GRE tunnel with the PCF (SC/MM) unit  330 , the CAG  350  performs LCP negotiation with the AT  310  (Step  329 ). Then, the CAG  350  transfers the CHAP challenge value to the AT  310 , which in turn transmits the CHAP response value to the CAG  350  (Step  337 ). In this case, the AT  310  generates NAI delivered to the CAG  350  during the CHAP authentication.  
         [0067]     Receiving the CHAP response value from the AT  310 , the CAG  350  analyzes the NAI to locate the AAA server  360  to which the AT  310  belongs. The CAG  350  generates an access request message delivered to the AAA server  360  (Step  333 ).  
         [0068]     Then the AAA server  360  analyzes the information of the NAI and CHAP challenge/response values contained in the access request message to perform service authentication. Completing the service authentication, the AAA server  360  transmits an access accept message generated in response to the access request message to the CAG  350  (Step  335 ). Upon receiving the access accept message, the CAG  350  generates a CHAP success message delivered to the AT  310  (Step  337 ).  
         [0069]     Completing successfully the CHAP authentication, the CAG  350  and the AT  310  performs IP configuration for a communication channel between them (Step  339 ). Namely, the CAG  350  allocates an IP address to the AT  310  according to the IP address allocation process by using Dynamic Host Control Protocol (DHCP) or IPCP.  
         [0070]     Thus, the BWA communication system can provide BWA communication services for a dual mode terminal connected to the CDMA 2000 1×EVDO communication system. Although the previous description in connection with  FIG. 3  relates the BWA communication services provided for the dual mode terminal connected to the CDMA 2000 1×EVDO communication system, the present invention shall not be limited to this case.  
         [0071]     Hereinafter in connection with  FIG. 4  is described the process of providing the BWA communication services for the dual mode terminal connected to the CDMA 2000 1×EVDO communication system according to the present invention. Firstly, described is the server RAS  415  placed in the BWA communication service region  420  that transmits a packet to a dual mode terminal  401 . The packet transmitted from the RAS  415  is delivered through the ACR  413  and IP network  411  to the CAG  409  that has allocated an IP address to the dual mode terminal  401 . Then the CAG  409  transfers the packet to the PCF (SC/MM) unit  407  of the CDMA 2000 1×EVDO communication service region  410  accessed by the dual mode terminal  401 . Consequently, the packet received by the PCF (SC/MM) unit  407  from the BWA communication service region  420  through the CAG  409  is transferred through the base station ANC/ANTS  403  to the dual mode terminal  401 .  
         [0072]     Secondly, described is a dual mode terminal  401  placed in the CDMA 2000 1×EVDO communication service region  410  that transmits a packet to the BWA communication service region  420 . As shown in  FIG. 4 , the packet transmitted from the dual mode terminal  401  is delivered through the ANC/ANTS  403  of the CDMA 2000 1×EVDO communication service region  410  to the PCF (SC/MM) unit  407 , which in turn delivers the packet to the CAG  409  that has allocated an IP address to the dual mode terminal  401 . Then, the CAG  409  delivers the packet through the IP network  411  and ACR  413  to the server RAS  415  placed in the BWA communication service region  420 . The packet transfer between the RAS  415  and CAG  409  is achieved by means of IP routing or IP switching. Also the packet transfer between the CAG  409  and the PCF (SC/MM) unit  407  is achieved by means of GRE tunnel.  
         [0073]     As described above, the present invention enables heterogeneous communication systems to cooperate for providing complementary communication services for the dual mode communication terminals. Particularly, the invention enables the BWA and CDMA 2000 1×EVDO communication systems to cooperate for providing complementary communication services, such that, if a dual mode communication terminal already connected to the BWA communication system moves to CDMA 2000 1×EVDO communication system, it may continuously receive the BWA communication services, or vice versa.  
         [0074]     While the invention has been shown and described with reference to a certain preferred embodiment thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.