Patent Document

CLAIM OF PRIORITY 
     The present application claims priority from Chinese application CN200510113517.2 filed on Oct. 17, 2005, the content of which is hereby incorporated by reference into this application. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a mobile network communication technique and particularly to a method and apparatus for handoff in mobile network communication. 
     2. Description of the Related Art 
     In a wireless communication system, handoff between different systems such as a mobile phone and a wireless local area network (WLAN) is performed according to user&#39;s necessity. 
       FIG. 1  is a view showing an example of configuration of a wireless communication system concerned with handoff between systems. In  FIG. 1 , the reference numeral  1  designates an information contents server;  2 , an IP network;  3 , a home agent (HA) server of mobile IP (MIP);  8 , a mobile station (MS);  5 , a wireless local area network (WLAN) provided by a WLAN service provider;  4 , a gateway (PDIF: Packet Data Inter-working Function) to the WLAN;  10 , a WLAN access point (AP);  7 , a mobile phone system (1×EvDO: 1× Evolution Data Only) network provided by a 1×EvDO service provider;  6 , a gateway (PDSN: Packet Data Serving Node) to the 1×EvDO network;  13 , a 1×EvDO access point (AP); and  15 , a stationary network. 
     When the MS  8  needs to change the 1×EvDO access point to the WLAN access point or when the MS  8  needs to change the WLAN access point to the 1×EvDO access point, the MS  8  sends mobile IP registration information to the home agent HA and asserts a new PPP (Point to Point Protocol) session between the gateway PDIF/FA as a target and itself. If the old PPP session between the gateway PDSN and the MS at that time were held so continuously as not to be cleared until timeout, not only would a great deal of resources become wasteful but also there would be a bad influence on access to other mobile stations. In addition, as a more serious problem, a user must pay an excessive fee even though the network has been already changed to another wireless network. 
     U.S. Patent Application Publication 2004/0082330A has proposed a method for warranting handoff by using mobile IP between a wireless LAN (WLAN) and a third generation (3G) network. In the proposed method, it was possible to warrant handoff in one direction from the WLAN to the 3G network but it was impossible to warrant handoff in a reverse direction. This is because this proposed method gave no consideration about how to release network side not-yet-changed resources after changing the network. 
     That is, in the proposed method, when the MS changes one gateway to another wireless LAN gateway, the MS sends mobile IP registration information to the home agent HA and asserts a new PPP session between the gateway PDIF/FA as a target and itself. If the old PPP session between the gateway before handoff and the MS were held so continuously as not to be cleared until timeout, not only would a great deal of resources become wasteful but also there was a bad influence on access to other mobile stations. As a more serious problem, the user must pay an excessive fee. 
     In the process in which CDMA 1×EvDO is changed to the WLAN, the MS performs registration in the home agent through the PDIF again. The method about how to cut off PPP connection, that is, which of the MS and the PDSN cuts off PPP connection, has never been proposed. 
     If PPP connection is cut off by the MS, the PDSN sends deregistration information to the home agent. There is however a possibility that error may be caused by the home agent&#39;s deletion of registration information in the MS even in the case where the deregistration information reaches to the home agent so that the MS is registered in the home agent through the WLAN. 
     SUMMARY OF THE INVENTION 
     An object of the present invention to provide a method and apparatus for handoff in a mobile network communication, in which when a user changes one gateway to another gateway, connection to the gateway before handoff is cut off immediately to thereby make it possible to save network resources. 
     According to an embodiment of the present invention, a server connected to a network in a wireless communication system is provided for accomplishing the object. The wireless communication system includes a mobile terminal with wireless interfaces, access points each communicating with the mobile terminal through one of the wireless interfaces so as to be connected to the network, and wireless network gateways each having one side connected to the server and the other side connected to corresponding one of the access points. The server includes a communication unit for wirelessly communicating with the mobile terminal through one of the wireless network gateways, and a processing unit for receiving registration request information from the mobile terminal through the communication unit and executing handoff from one wireless interface to another wireless interface. The processing unit sends a signal instructing the termination of wireless connection generated by the processing unit to the wireless network gateway through the communication unit to release wireless connection before handoff between the server and the access point when the registration request information indicates the termination of the current wireless connection. 
     Other objects, features and advantages of the invention will become apparent from the following description of the embodiments of the invention taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram showing an example of configuration of a wireless communication system concerned with handoff between systems; 
         FIG. 2  is a view showing a mobile IP signal process in a wireless LAN (WLAN) in the present invention; 
         FIG. 3  is a view showing a flow of data in the wireless LAN (WLAN) in the present invention; 
         FIG. 4  is a schematic view showing C/W extension in mobile IPv4 registration request information in the present invention; 
         FIG. 5  is a schematic view showing contents of C/W extension in the mobile IPv4 registration request information in the present invention; 
         FIG. 6  is a registration table in a home agent in the present invention; 
         FIG. 7  is a signal process for handoff between a CDMA 2000 1×EvDO network and a wireless LAN; 
         FIG. 8  is a view showing a basic function of a mobile station; 
         FIG. 9  is a view showing a basic function of the home agent; 
         FIG. 10  is a view showing a basic function of PDSN; 
         FIG. 11  is a flow chart showing a control process after the home agent receives RRQ information from PDIF; 
         FIG. 12  is a flow chart showing a control process after PDSN receives RRP; 
         FIG. 13  is a flow chart showing a control process in which the mobile station sends RRP; 
         FIG. 14  is a block diagram showing the configuration of the home agent HA; 
         FIG. 15  is a block diagram showing the configuration of the wireless gateway; and 
         FIG. 16  is a block diagram showing the configuration of the mobile station. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     An embodiment of the invention will be described with reference to the accompanying drawings. 
       FIG. 1  is a view showing network topology of handoff between a CDMA 1×EvDO network and a wireless LAN. As shown in  FIG. 1 , a mobile station MS performs registration in the CDMA 1×EvDO network through an access point AP and a gateway PDSN. The gateway PDSN has a foreign agent (FA) function. The mobile station can also perform registration in a wireless LAN (WLAN) through an access point AP and a gateway PDIF. The gateway PDIF also has a foreign agent (FA) function. An AAA (Authentication Authorization and Accounting) server not shown in  FIG. 1  serves as a RADIUS (Remote Authentication Dial-In User Service) server for chiefly performing authentication and accounting of the mobile station. 
     Various kinds of wireless interfaces such as W-CDMA and Blue-tooth as well as CDMA 1×EvDO and wireless LAN may be used as network interfaces in this invention. 
     A web site “3rd Generation Partnership Project 2” is a good guide to control signals and data processes for CDMA 2000 1×EvDO.  FIG. 2  is a view showing control signal protocol stacks on the WLAN side. The mobile station supports PPPoE (Point to Point Protocol over Ethernet) and performs authentication through the AAA server. Mobile IP protocol stacks which support an application layer of the mobile station performs handoff between the 3G network and the WLAN. The WLAN access point is only a layer-2 network device, so that a flow of all control signals and data are open to the AP. 
     On the other hand, the gateway PDIF terminates PPPoE and supports authentication. This is because the PDIF has a function of a foreign agent which can communicate with the home agent on the basis of mobile IP information. 
       FIG. 3  is a view showing data flow protocol stacks on the WLAN side. Data are transmitted between the PDIF and the home agent HA through IP in IP tunnels, so that the data finally reach the mobile station. 
     When the mobile station changes the 1×EvDO network to the wireless LAN side, PPP connection between the PDSN and the mobile station is continued until the PPP connection is cut off by timeout, unless the mobile station dynamically cuts off the PPP connection. 
     In this invention, mobile IP registration request information RRQ sent from the mobile station to the home agent HA is extended to thereby indicate the current wireless connection of the mobile station and notify the home agent HA of the interruption of PPP connection. 
       FIG. 4  is a schematic view of mobile IPv4 registration request information including a C/W extension field. The signal shown in  FIG. 4  contains items and extended items such as type, duration, local address, home agent, care of address, identification, etc. In this invention, extended contents shown in  FIG. 5  are used as definitions of extended items. 
       FIG. 5  is a schematic view showing contents of the C/W extension field in the mobile IPv4 registration request information ( FIG. 4 ) according to the invention. In  FIG. 5 , the “Type” means a numerical value such as 149, the “Length” means a length expressed by a numerical value such as 16, the “C/W Flag” means mark bits such as 8 bits, and the “PPP Disconnection” means the mobile station&#39;s requirement for PPP disconnection. In this embodiment, “C” in “C/W Flag” means a CDMA network, and “W” in “C/W Flag” means a wireless LAN. The “C” and “W” are not limited thereto and may mean other networks. When PPP disconnection is asserted, the home agent HA needs to notify the PDSN of the mobile station&#39;s requirement for PPP disconnection. The “PPP Disconnection” is only one example. The “PPP Disconnection” may be replaced by a selection item such as “Stop of Accounting” or “Release of Resources”. 
     Next, a registration table for the home agent HA will be described with reference to  FIG. 6 . Each record of the registration table includes a home address HoA  601 , a care-of-address CoA  602 , an identification  603 , and a Lifetime  604 , which belong to the mobile station to be registered. Each record of the registration table is registered according to the mobile IPv4 registration request which format is shown in  FIG. 4 . On this embodiment, the mobile IPv4 registration table is extended so that the home agent HA is notified of whether the current registration is derived from the CDMA 2000 1×EvDO network or from the wireless LAN. The “C/W” flag  605  is added to the registration table, so that registration is performed while classified into the CDMA 2000 1×EvDO network and the wireless LAN with the character “C” or “W”. 
       FIG. 7  is a view showing a control signal process for handover between the CDMA 2000 1×EvDO network and the wireless LAN. First, the mobile station  8  starts PPP connection to the gateway PDSN  6  ( 701 ). The gateway PDSN  6  allocates a home address HoA to the mobile station  8  through authentication by the AAA server  16  on the basis of NAI (Network Access Identifier) information of the mobile station  8  ( 702 ). At the same time, the gateway PDSN  6  performs registration in the home agent HA  3  by using the home address HoA of the mobile station  8  and the IP address of itself ( 703  and  704 ). In this manner, data sent from a correspondent node  17  (CN not shown in  FIG. 1 ) to the mobile station  8  pass through the mobile IP tunnel between the gateway PDSN  6  and the home agent HA  3  and reach the mobile station  8  ( 705 ). 
     As the mobile station  8  comes into a wireless LAN region ( 706 ), the mobile station  8  first performs negotiation with the wireless LAN access point AP  13 . The user can acquire basic information such as fee, bandwidth, signal strength, service quality, etc. from the wireless LAN side on the basis of this negotiation. After the negotiation between the mobile station  8  and the gateway PDIF  4 , the mobile station  8  acquires the same home address HoA from the AAA server  16  in order to obtain network PPPoE access authentication by using the same mobile station NAI ( 707 ,  708  and  709 ). 
     When the user decides a network to be connected in accordance with the user&#39;s situation, that is, when, for example, connection to the wireless LAN is decided ( 710 ), the mobile station  8  sends RRQ information with new C/W extended options proposed by this invention to the gateway PDIF  4  for the wireless LAN ( 711 ). Upon reception of the information, the home agent HA  3  changes the network connection from “C” to “W” in accordance with its own registration table information ( 712  and  713 ) and sends the RRQ information back to the mobile station  8  through the gateway PDIF  4  ( 714  and  715 ). Then, the home agent HA  3  sends HA-FA (Home Agent—Foreign Agent) information and notifies the gateway PDSN  6  of the requirement for the termination of PPP connection ( 716  and  717 ). 
     Finally, the data flow is sent to the mobile station  8  through the tunnel between the home agent HA  3  and the gateway PDIF  4  ( 718 ). 
     The functional block configuration of each device in this invention will be described below. 
       FIG. 8  is a view showing functional blocks of the mobile station  8 . The mobile station  8  is a dual mode terminal which has an EvDO card  804  used for 1×EvDO connection, and a wireless LAN card  805  used for wireless LAN connection. A handover trigger function  803  is an option for deciding whether the user performs handoff or not, and which wireless connection is used. The Mobile IP MN (Mobile Node)  802  is the mobile IP function for the mobile station  8 . The mobile station  8  needs to support the C/W extension function  801  of the mobile IP. 
       FIG. 9  is a view showing functional blocks of the home agent HA  3 . The C/W extension of the home agent registration table permits the judgment as to which wireless network is currently connected with the home agent, that is, the judgment as to which of 1×EvDO or wireless LAN is used currently. At the same time, the home agent  3  must support the C/W extended options of the mobile IP as the C/W extension function  901 . The Mobile IP HA (Home Agent)  902  is the mobile IP function for the HA 3 . The Registration Table  903  is a basic registration table of the Mobile IP. Finally, the home agent  3  notifies the gateway PDSN  6  of the requirement for PPP disconnection. 
       FIG. 10  is a view showing functional blocks of the gateway PDSN  6 . The PDSN  1004  is a basic function of the PDSN  6 . Besides basic functions, C/W extension must be supported by the gateway PDSN  6  as the C/W extension function  1001  so that the gateway PDSN  6  communicates with the home agent HA  3  in order to find whether the mobile station  8  is connected through the CDMA network or whether registration is performed through the wireless LAN. The PDSN  1004  must support HA-FA information so that PPP connection with the mobile station is cut off on the basis of the HA-FA information. The Mobile IP FA (Foreign Agent)  1002  is the mobile IP function for the PDSN  6 . The Registration Table  1003  is a basic registration table of the Mobile IP. 
       FIG. 11  is a flow chart showing a control process in the home agent HA  3 . The process corresponds to sequence from  711  to  714  of  FIG. 7 . After the home agent HA  3  receives RRQ information through the gateway PDIF  4  (S 1101 ), the home agent HA  3  updates its own registration table (S 1102 ) and sends standard RRP back to the gateway PDIF  4  (S 1103 ). Then, the home agent HA  3  makes a decision on the basis of the C/W extended options as to whether the gateway PDSN  6  is notified of the requirement for PPP disconnection or not (S 1104 ). If the C/W extended option is “W” (means yes), the home agent HA  3  notifies the gateway PDSN  6  of the requirement for PPP disconnection (S 1105 ). 
       FIG. 12  is a flow chart showing a control process in the gateway PDSN  6 . The process corresponds to sequence from  716  to  717  of  FIG. 7 . After the gateway PDSN  6  receives registration information from the home agent HA  3  (S 1201 ), the gateway PDSN  6  first judges based on the received registration information whether network resources are to be deleted or not (S 1202 ). When, for example, the judgment is “Yes” in the case of PPP, PPP connection is cut off (S 1203 ). When the information is invalid, the gateway PDSN ignores the information. 
       FIG. 13  is a flow chart showing a control process in the mobile station  8 . The process corresponds to sequence  711  of  FIG. 7 . When the mobile station  8  sends RRQ information (S 1301 ), the mobile station  8  first judges by, for example, the handover trigger function whether the mobile station is currently connected to the wireless LAN or to the 3G network (S 1302 ). When the mobile station  8  is currently connected to the wireless LAN, “W” is identified in this extended option (S 1304 ). When the mobile station is currently connected to the CDMA (3G) network, “C” is identified in this extended option(S 1303 ). At the same time, the RRQ with the C/W extended option is sent from the mobile station  8  (S 1303 , S 1304 ). The RRQ with the C/W extended option works to release (delete) the network resouces (such as ppp connection) assigned to the mobile station  8  before the handover. 
       FIG. 14  is a block diagram showing the configuration of the home agent HA  3 . The home agent HA  3  includes a communication unit  1401 , a processing unit  1403 , and a database unit  1404 . Of these units, the communication unit  1401  receives handoff request information from the mobile station  8  and performs handoff from one wireless interface to another wireless interface. For example, the request information has an extension for specifying the termination of connection between the network side server and the access point before handoff. A process executed by the processing unit contains a basic process  1406 , and a PPP C/W process  1407 . Upon detection of received information, the communication unit  1401  generates a signal and notifies the wireless network gateway of the requirement for the interruption of wireless connection. Accordingly, the processing unit  1403  can process the PPP disconnection request and add a C/W connection identifier, etc. to the registration table. The database unit  1402  includes a basic registration table  1404  and a C/W extension table  1405 . General communication data are stored in the basic registration table  1404 . The registration table of the home agent HA shown in  FIG. 6  is stored in the basic registration table  1404  and the C/W extension table  1405 . 
       FIG. 15  is a block diagram showing the configuration of the gateway  4  and  6 . The gateway includes a communication unit  1501 , a processing unit  1503 , and a database unit  1502 . The functions of the respective units are like those of the home agent HA  3 . In addition thereto, the processing unit  1503  can execute a PPP disconnection process and delete network resources of the mobile station  8  assigned before handover. 
       FIG. 16  is a block diagram showing the configuration of the mobile station  8 . The mobile station  8  includes two types of communication units  1601  and  1602 , a processing unit  1604 , and a database unit  1603 . The functions of the respective units are like those of the home agent HA. In addition thereto, the processing unit  1604  can add an extended function, inclusive of a request for the deletion of network resources of the home agent before handoff such as a PPP session, into the mobile IP registration information and add a 3G/WLAN network connection identifier to the registration table of the home agent. 
     It should be further understood by those skilled in the art that although the foregoing description has been made on embodiments of the invention, the invention is not limited thereto and various changes and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.

Technology Category: 5