WO2004017658A1

WO2004017658A1 - Cross-ip internet roaming method for mobile terminal

Info

Publication number: WO2004017658A1
Application number: PCT/CN2003/000642
Authority: WO
Inventors: Ning Zhang; Xiaohui Wan
Original assignee: China Iwncomm Co., Ltd
Priority date: 2002-08-15
Filing date: 2003-08-07
Publication date: 2004-02-26
Also published as: CN1133350C; AU2003255101A1; CN1420705A

Abstract

An active Address Resolution Protocol is used in the present invention, and thus a method is achieved which allows the mobile terminal to roam in different IP networks without modifying the routing entry of the mobile terminal, and therefore enables the conventional TCP/IP protocol to support the mobility. When determining that it has roamed to a foreign network by receiving the notification of the foreign agent, the mobile terminal would perform the active address resolution protocol so as to bind the MAC address of the foreign agent (8) to the IP address of default gateway of the mobile terminal (5) in the ARP cache, and the mobile terminal would set its attribute static when modifying the ARP cache. When determining it has returned to the home networks from the foreign networks, the mobile terminal would clear the ARP cache, thereafter it would establish an ARP cache table in accordance with the normal ARP operation, resume the attribute of the ARP cache to be dynamic and perform the normal transmission and reception of IP data.

Description

Method for implementing mobile terminal cross-IP internet roaming

The present invention relates to a method for mobile terminal to perform data communication in different Internet Protocol (IP) networks, and in particular, to an Active Address Resolution Protocol (Active ARP) protocol for implementing mobile terminals in the IP network. Seamless roaming method.

Background technique

Internet Protocol With the rapid development of the Internet, IP has become one of the most important standards in the field of data communications. In addition to the Internet, this protocol is also widely used in a variety of network environments such as corporate networks and campus networks. At present, the Internet has become the world's largest information database, providing people with services such as World Wide Web (WWW) browsing, file transfer protocols, FTP, and e-mail; meanwhile, many new network services such as Voice over IP, VoIP, and VOD on the Internet And so on. In addition, the development of wireless communication technologies, such as 802.11 and Bluetooth technologies, and the popularity of high-performance, low-cost mobile terminal devices that provide IP connectivity, such as laptop computers, PocketPCs, PocketPCs, personal digital assistants, PDAs, etc. The release of network cable restraints has greatly changed the way people live and work, and people hope to access the network anytime, anywhere. However, the existing TCP / IP protocol does not provide support for terminal mobility, which is determined by the addressing method and routing algorithm. In the TCP / IP protocol, all network devices must have an IP address for data exchange. In fact, the IP address is directed to the network connection and not to the network device. Therefore, when a terminal moves from one IP subnet to another, it must change its IP address to access the network. The upper layer protocols, such as TCP, use port numbers and IP addresses to identify network connections. When the IP address of a terminal device changes, its TCP connection is also interrupted. The same problem exists with the User Datagram Protocol (UDP) protocol. Currently, more than 95% of application services on the Internet are based on the TCP protocol. Therefore, to maintain seamless roaming of terminals between IP subnets, their IP addresses must remain unchanged. This requires a new proposal for the existing TCP / IP protocol. s solution.

Mobile IP protocol request evaluation RFC2002 (IP Mobility Support) (Request For Comment 2002) proposes a method to support the mobility of terminals. In the original network extension On the basis of Park, three roaming entities: Home Agent, Foreign Agent, and Mobile Terminal are introduced. The home agent and the foreign agent are collectively called mobile agents. See Figure 1 for its network structure. Each IP subnet 1, 6, 11 is connected to the Internet 10 through its own routers 2, 7, 13. The IP subnet to which the mobile terminal 5 belongs is referred to as the home network 1, and the IP subnets 6 and 11 other than the home network 1 are referred to as foreign networks. The home network 1 includes a terminal 4, a home agent 3, a mobile terminal 5, and a router 2 connected to the Internet 10. The foreign network 6 includes a foreign agent 8. Among them, the home agent 3 mainly completes the identity authentication and location management of the mobile terminal 5, intercepts the datagram sent to the mobile terminal 5, and forwards the datagram to the corresponding foreign agent 8 according to RFC2003 (IP encapsulation in IP). . The foreign agent 8 serves as the default router of the mobile terminal 5 in the foreign network 6, assisting the mobile terminal 5 to forward the identity authentication information and care-of address to the home agent 3, and at the same time unpacks the datagram that the home agent 3 forwards to the mobile terminal 5 through the tunnel, sends To mobile terminal 5; Mobile terminal 5 refers to a terminal device that can seamlessly roam between different IP subnets and maintain its IP address unchanged during roaming.

Referring to Figure 1, the working process of the RFC2002 protocol can be described as follows:

1]. The mobile terminal 5 uses the proxy announcement message to detect its own status, that is, whether its own location is at home network 1 or foreign network 6. If it is on the home network 1, go to step 5]; if it is on the foreign network 6, obtain the care-of address, which is usually the IP address of the foreign agent 8.

2]. The mobile terminal 5 performs identity authentication to the home agent 3 through the foreign agent 8 and notifies the care-of address.

3]. The home agent 3 intercepts the IP datagram sent to the mobile terminal 5 and sends it to the foreign agent 8 using the tunnel;

4]. The foreign agent 8 takes out the IP datagram sent to the mobile terminal 5 from the tunnel, and forwards it to the mobile terminal 5;

5]. The mobile terminal 5 sends and receives IP datagrams according to the IPv4 protocol.

It can be seen from the above that the mobile terminal 5 judges its current position and status by receiving the proxy announcement, and takes corresponding actions to cooperate with the home agent 3, the foreign agent 8 to realize roaming across the IP subnet:

[1]. If the mobile terminal 5 is on the home network 1 and does not roam, it will normally send and receive datagrams as other terminals; 〖2】. If the mobile terminal 5 is on the foreign network 6, it will be based on the foreign agent 8. The proxy announcement sets the default routing entry of this node to the current IP address of the foreign agent 8, deletes the original default routing entry and the direct routing entry pointing to the home network 1, and then sends the foreign agent 8 to the home agent 3 Register and announce your current location; [3]. If the mobile terminal 5 returns to the home network 1 from the foreign network 6, the corresponding default router 2 should also be set as the default gateway of the home network 1, and add a direct link to the home network 1. Routing entry.

Therefore, dynamically modifying the routing table of the mobile terminal 5 is one of the key steps for implementing the mobile IP protocol. Windows 95/98 / Me and other operating systems do not support dynamic modification of the routing table. Modifications to the routing table do not take effect until the system is restarted. This will inevitably cause mobile terminal 5 to move between different IP subnets. This kind of network application is interrupted and cannot support IP mobility. For example, when mobile terminal 5 roams between IP subnets, network applications such as the World Wide Web www browser, file transfer protocol FTP, and email will be interrupted. Many real-time network applications, such as video on demand VOD, IP voice VoIP, and web conferencing, etc. Unable to achieve, causing time and economic loss. In view of the absolute market share of terminal operating systems such as Windows, this has seriously hindered the application and promotion of mobile IP technology. If the operating system such as Windows is to support the Mobile IP protocol, the TCP / IP protocol stack must be rewritten. The TCP / IP protocol stack occupies a large proportion of the entire operating system. Many commercial operating systems do not provide the TCP / IP protocol stack. The source code is, therefore, difficult to modify and work on the TCP / IP protocol stack, and it is cumbersome to use and install for ordinary users.

Summary of the Invention

The present invention is to solve the technical problem that the mobile terminal must dynamically modify the routing table in the background art. To this end, the present invention provides an active ARP, and uses it to implement a method that can ensure that mobile terminals roam across IP subnets without modifying the routing table entries of the mobile terminal, thereby providing mobility support for the traditional TCP / IP protocol

The technical solution of the present invention is:

A method for implementing mobile terminal cross-Internet protocol internet roaming using an active address resolution protocol. The Internet protocol network includes a network that is a home network of the mobile terminal and one or more networks that are foreign networks of the mobile terminal. The method includes:

The mobile terminal receives the proxy announcement of the mobile agent;

The mobile terminal judges whether it roams to a new IP subnet according to the proxy announcement, If yes, the mobile terminal executes an active address resolution protocol, and sends and receives its address resolution ^ '_,', 'If no, the mobile terminal continues to listen to the proxy announcement.

Preferably, the mobile terminal executes an active address resolution protocol and actively modifies its address resolution protocol cache, including actively binding an Internet protocol address of a default gateway of the mobile terminal in the address resolution protocol cache, and the mobile The Internet protocol address binding of each terminal in the terminal's home network, and the mobile agent includes a home agent in the home network and a foreign agent in the foreign network.

According to an aspect of the present invention, the binding of the Internet protocol address includes: when the new IP subnet is a foreign network, setting the default gateway of the mobile terminal and the Internet protocol of each terminal in the home network of the mobile terminal The address is bound to the media access control address of the foreign agent in the foreign network, and the attribute of the address resolution protocol cache is set to static. When the new IP subnet is its home network, the mobile terminal first clears its address. The address resolution protocol cache is then established according to a normal address resolution protocol operation, and the attributes of the address resolution protocol cache are restored to dynamic.

According to another aspect of the present invention, the binding of the Internet protocol address includes: allocating an Internet protocol address of a default gateway of the mobile terminal and an Internet protocol address of each terminal in a home network of the mobile terminal to the new IP subnet. The media access control address of the mobile agent in the network is bound, and the attribute of the address resolution protocol cache is set to static.

According to another aspect of the present invention, the new IP subnet is the home network (1), which means that the mobile terminal (5) has just returned to the home network (1) from the foreign network (6), and the handover has not been completed. The new IP subnet is a foreign network including mobile terminals roaming between different foreign networks or roaming from a home network to a foreign network. The mobile terminal judges that it has roamed to a new IP subnet by using the information in the received proxy announcement of the mobile agent. The mobile terminal obtains the media access control address of the mobile agent through the agent announcement.

According to another aspect of the present invention, the binding of the Internet protocol addresses of the terminals in the home network of the mobile terminal is to use the subnet mask of the Internet protocol address of the home network to derive the Internet protocol addresses of the terminals in the home network Range.

With the above embodiments, the present invention has the following advantages: When the mobile terminal adopting the above method moves between different IP subnets, various network applications will not be interrupted, and support for IP mobility can be realized, which is economical and saves time; and because the mobile terminal adopting the active ARP protocol is based on a proxy The content of the announcement determines its current status and location, and then actively operates the ARP cache table. The mobile terminal can roam between different IP subnets without modifying the routing table. Therefore, when the operating system such as Windows supports the Mobile IP protocol, There is no need to rewrite the TCP / IP protocol stack. Therefore, the workload is greatly saved, and the use and installation are simplified. The present invention can be applied to most operating systems on the market including Windows, and has strong portability and practicality, thereby greatly increasing the application range of mobile IP technology.

Brief description of the drawings:

FIG. 1 is a schematic diagram of a mobile IP subnet topology structure in which the method of the present invention can be used;

FIG. 2 is a flowchart of an operation of a mobile terminal across IP Internet roaming using the method of the present invention; FIG.

Fig. 3 is a correspondence table of IP addresses and MAC addresses of some network devices in Fig. 1; Fig. 4 is an ARP cache table when the mobile terminal in Fig. 1 is on a home network;

Figure 5 shows the ARP cache table when the mobile terminal is in a foreign network.

detailed description

The invention adopts the active ARP protocol, instead of passively modifying its own ARP cache according to the content in the ARP request or response datagram. The mobile terminal judges its current state and location according to the content in the proxy announcement, and then actively The ARP cache table operates so that you can roam between different IP subnets without modifying the routing table.

The operation flowchart of the mobile terminal's cross-IP internet roaming using the method of the present invention is described in FIG. 2. In the figure, the mobile terminal 5 is in the home network 1 during initial communication (step 200). The mobile terminal 5 continuously listens to the proxy announcement. Once the proxy announcement is received (step 210), it is determined whether to roam to a new IP subnet based on the proxy announcement (step 220), if:

1]. If yes, determine whether the new IP subnet is a foreign network 6 (step 230). ①. If yes, for example, when the mobile terminal 5 roams from the home network 1 to the foreign network 6 or from the foreign network 11 to the foreign network 6, the active ARP protocol is executed, and the IP address of the default gateway of the mobile terminal is stored in the address resolution protocol cache. The address is bound to the media access control MAC address of the foreign agent (Step 241), and bind the IP address of each terminal in its home network 1 to the MAC address of the foreign agent (step 242), the mobile terminal sets its attributes to static when modifying the ARP cache (step 243), and then continues Listening agent announcement; ② If not, for example, when the mobile terminal 5 returns from the foreign network 6 to the home network 1, preferably, the mobile terminal 5 needs to clear the ARP cache (step 231), and then the ARP can be established according to normal ARP operations. Cache the table, send and receive normal IP datagrams, and continue to listen to proxy announcements.

2]. If there is no roaming, that is, when the mobile terminal moves in the home network or foreign network without roaming, it will send and receive datagrams according to the standard IPv4 protocol like other terminals, and continue to listen to proxy announcements.

The above roaming to a new IP subnet means that the mobile terminal finds that its IP subnet has changed by listening to the proxy announcement.

The definition of each roaming entity in the present invention is the same as that of RFC2002, and relates to home agents, foreign agents and mobile terminals. The methods of proxy announcement, tunnel technology, mobile terminal identity authentication, and location management defined in RFC2002 are also applicable to the present invention.

The specific implementation method of the present invention will be described below in detail with reference to FIG. 1 and FIGS. 3 to 5. For the convenience of explanation, a correspondence table of some network devices in the network and their IP addresses and MAC addresses is given in FIG. 3.

1. Mobile home network

The mobile terminal home network refers to a situation where the home network and the mobile terminal return to the home network from a foreign network when the mobile terminal initially communicates, and the handover has been completed. At this time, the mobile terminal sends and receives datagrams that conform to the IPv4 protocol, just like other terminals. Assume that mobile terminal 5 is communicating with terminal 4 in its own network and terminal 12 in other IP networks 11. Through normal ARP operations, its ARP cache table should contain the binding of IP addresses and MAC addresses of router 2 and terminal 4, See Figure 4 for the corresponding relationship.

2. Mobile terminal in foreign network

A mobile terminal in a foreign network refers to a situation where the mobile terminal roams between different foreign networks or just moves from a home network to a foreign network. When the mobile terminal 5 determines that it has moved to the foreign network 6 by receiving the proxy announcement of the foreign agent 8, at this time, the mobile terminal 5 does not matter whether the mobile terminal 5 moves from the home network 1 or the foreign network 11 to the foreign network 6. The active ARP protocol will be implemented: the IP address of the default gateway and the MAC address of the foreign agent 8 will be hosted in the ARP cache Dynamically bind, and use the subnet mask of the IP address of home network 1 to calculate the range of the IP addresses of other network devices in home network 1, and bind each IP address to the MAC address of the foreign agent 8. At this time, it The ARP cache table is shown in FIG. 5.

When the mobile terminal 5 wants to communicate with the terminal 12 in the foreign network 11, since the terminal 12 does not belong to its home network 1, the datagram sent to the terminal 12 should be forwarded through the default gateway. By querying the ARP cache table, the mobile node will use the foreign agent The MAC address of 8 sends a datagram. In this way, the datagram will be directly sent to the foreign agent 8, and the foreign agent 8 has a routing function, and it will forward accordingly according to the destination IP address in the datagram. When the mobile terminal 5 communicates with the terminal 4, it will also send datagrams and addresses according to the corresponding entries in the ARP cache table. Therefore, the datagrams sent to the terminal 4 will also be directly sent to the foreign agent 8, and then the foreign agent 8 forwards. In this way, without changing the routing table, the datagrams sent by the mobile node to the home network 1 and the foreign network nodes when roaming across the IP subnet can be forwarded by the foreign agent 8. The above operation on the ARP cache table is different from the case where the standard ARP operation is passively changed according to the ARP response message. Instead, the mobile node actively binds the IP address and the MAC address, so the protocol is called the active ARP protocol. Considering that in many operating systems, the ARP cache is automatically cleared periodically or irregularly, the mobile terminal 5 should set its attributes to static when changing the binding of the ARP cache in the foreign network 6 to ensure that it will not be updated by the system.

3. Mobile terminal returns to home network

The return of the mobile terminal 5 to the home network 1 means that the mobile terminal 5 has just returned to the home network 1 from the foreign network 6 and has not yet completed the handover. The mobile node can determine from the agent announcement and the current status of the home agent 3 that it is already on the home network 1. At this time, it should clear the ARP cache table and restore the ARP cache properties to dynamic in response to its location change. It can then rebuild the ARP cache table and send datagrams through normal ARP operations.

The communication process between the mobile terminal and other terminals in different states is described in detail below with reference to FIG. 1.

Mobile terminal 5 uses the normal ARP operation on home network 1 to implement communication with fixed hosts on the local network. The working process is as follows: If mobile terminal 5 wants to communicate with terminal 4 on the same network when it is on home network, first mobile terminal 5 must query its own routing table. In order to determine the position of the terminal 4 to be communicated in the network through the routing table, the mobile terminal 5 judges the IP of the terminal 4 through the routing table. The address IP_T4 and the subnet mask find that terminal 4 and the mobile terminal device are on the same network segment, so mobile terminal 5 starts to query its own ARP cache table. If the corresponding ARP cache table does not have the IP address of terminal 4 IP_T4 and its MAC address For the binding of MACJT4, the mobile terminal 5 will broadcast the MAC address with the IP address of IP-T4 in the local network through the ARP request broadcast. This broadcast will be obtained by all terminal devices in this network, so all terminal devices in this network will check whether their IP address is the same as the requested IP-T4 address, so only terminal 4 will respond to mobile terminal 5 ’s Respond to the ARP request, send the MAC address of the machine MAC_T4 back to the mobile terminal 5 together with the IP address of the machine, and add the MAC address of the mobile terminal MAC_T5 to the ARP cache table of the machine. Mobile terminal 5 After receiving the ARP response, the MAC address MAC_T4 of terminal 4 is also added to the local ARP cache table, so the connection between mobile terminal 5 and terminal 4 is formed, and normal IPv4 protocol compliance can be performed between them. Datagram sending and receiving.

In FIG. 1, when the mobile terminal 5 is in the home network 1, to communicate with the terminal 12 in another network 11, the mobile terminal 5 first needs to query its own routing table, so as to determine from the routing table that the terminal device to be communicated is in the network. At the location, the mobile terminal 5 finds that the terminal 12 and the mobile terminal 5 are in different network segments by judging the IP address of the terminal 12 IP_T12 and the subnet mask, and the mobile terminal 5 directly requests its router 2 (IP_GW) Router 2 sends its own MAC address MAC-GW together with its own IP address IP-GW to mobile terminal 5, and adds the MAC address MAC_T5 of mobile terminal 5 to the local ARP cache table After receiving the ARP response, mobile terminal 5 also adds the MAC address MAC_GW of router 2 to the local ARP cache table. Next, router 2 forms a connection between mobile terminal 5 and terminal 12 through its routing function. Data packets can be sent and received normally in accordance with the IPv4 protocol.

The mobile terminal's access to the network equipment when roaming can be described in detail based on the two cases where the communication peer is not a terminal in the home network and the communication peer is a terminal in the home network.

In FIG. 1, the mobile terminal 5 moves from the home network 1 to the foreign network 6. When the mobile terminal 5 determines that it has moved to the foreign network 6 by receiving the proxy announcement of the foreign agent 8, then the mobile terminal 5 first moves from the agent Obtain the MAC address MAC_FA of the foreign agent 8 in the announcement, and actively bind the IP address of the default gateway IP — GW and the MAC address of the foreign agent 8 in the ARP cache, and use the subnet mask of the home network IP address. The code calculates the range of IP addresses of other network devices in the home network 1, and binds each IP address to the MAC address of the foreign agent 8.

If the mobile terminal 5 is to communicate with the terminal 12 in the foreign network 11, the mobile terminal 5 finds that the terminal 12 and the mobile terminal device are in different network segments by judging the IP address of the terminal 12 IP-T12 and the subnet mask. The mobile terminal 5 5 does not send an ARP request broadcast on the entire network segment, but directly requests the MAC address of its router 2 (IP_GW), so the datagram sent to terminal 12 should be forwarded through the default gateway to query the ARP cache table. At this time, the ARP cache table The IP address of the default gateway IP_GW and the MAC address of the foreign agent 8 have been actively bound. The datagram will be directly sent to the foreign agent 8 according to the bound MAC address MAC-FA, and the foreign agent 8 will add a mobile terminal 5 routing entry to its routing table. At the same time, because the foreign agent 8 has a routing function, it Corresponding forwarding will be performed according to the destination IP address in the datagram. Thus, normal communication between the mobile terminal 5 and the terminal 12 in the foreign network 6 can be achieved.

If the mobile terminal 5 is to communicate with the terminal device 9 of the foreign network 6, the mobile terminal 5 first queries its own routing table, so as to determine the position of the terminal device to be communicated in the network through the routing table. The mobile terminal 5 By judging the IP address of the terminal 9 and the subnet mask of the terminal 9 and finding that the terminal 9 and the mobile terminal device are on different network segments, the mobile terminal 5 will not send an ARP request broadcast on the entire network segment, but directly requests its router 2 ( IP_GW), and since the IP address of the default gateway IP-GW in the ARP cache table has been actively bound to the MAC address of the foreign agent, the data packet will be directly sent to the foreign agent 8, and the foreign agent 8 It is determined that the terminal 9 and the terminal 9 are in the same network segment, and then a datagram can be forwarded to the terminal 9 through a normal ARP protocol, so as to achieve normal communication between the mobile terminal 5 and the terminal 9 of the foreign network 6 after moving to the foreign network 6.

In FIG. 1, the mobile terminal 5 moves from the home network 1 to the foreign network 6, and communicates with the terminal 4 of the home network 1 as follows. First, the mobile terminal 5 needs to query its own routing table, so as to determine the terminal device to be communicated through the routing table. In the position in the network, the mobile terminal 5 finds that the terminal 4 and the mobile terminal device are in the same network segment by judging the IP address IP_T4 of the terminal 4 and the subnet mask, and then queries its own ARP cache table. A binding entry between the MAC of the terminal 4 and the foreign agent 8 already exists in its ARP cache table, so the mobile terminal 5 will forward it directly to the foreign agent 8, and the foreign agent 8 will send it according to its routing function. The data is forwarded to the terminal 4 so as to realize the normal communication between the mobile terminal 5 and the terminal 4 of the home network 1 after moving to the foreign network 6.

After the mobile terminal 5 returns to the home network 1, it can be determined from the information in the agent announcement of the home agent 3 that it is already on the home network 1. At this time, the mobile terminal 5 automatically clears the binding entries in its ARP cache table, and then it can Through normal ARP operations, the ARP cache table is rebuilt and datagrams are sent.

Claims

Rights request

A method for implementing mobile terminal cross-Internet protocol Internet roaming, characterized in that the method includes:

The mobile terminal (5) receives the agent announcement of the mobile agent (3, 8);

The mobile terminal (5) judges whether it roams to a new IP subnet (6) according to the proxy announcement,

If so, the mobile terminal (5) executes an active address resolution protocol, and actively modifies its address resolution protocol cache so that the mobile terminal (5) maintains normal Internet protocol datagram sending and receiving,

If not, the mobile terminal (5) continues to listen to the proxy announcement.

2. The method for implementing mobile terminal cross-Internet protocol internet roaming according to claim 1, characterized in that: the mobile terminal (5) executes an active address resolution protocol and actively modifies its address resolution protocol cache is included in the The address resolution protocol cache actively binds the Internet protocol address of the default gateway of the mobile terminal and the Internet protocol address of each terminal in the home network of the mobile terminal, and the mobile agent includes a home agent in the home network. (3) and foreign agents in the foreign network (8).

3. The method for implementing mobile terminal cross-Internet protocol internet roaming according to claim 2, characterized in that: the binding of the Internet protocol address comprises: when the new IP subnet is a foreign network (6), Bind the default gateway of the mobile terminal and the Internet protocol address of each terminal in the home network of the mobile terminal to the media access control address of the foreign agent (8) in the foreign network (6), and cache the address resolution protocol Is set to static, and when the new IP subnet is its home network (1), the mobile terminal (5) first clears its address resolution protocol cache, and then establishes the address resolution protocol cache according to normal address resolution protocol operations. And restore the cached attributes of the geocoding protocol to dynamic.

4. The method for implementing cross-Internet protocol internet roaming of a mobile terminal according to claim 2, characterized in that: the binding of the Internet protocol address comprises: an Internet protocol address of a default gateway of the mobile terminal and the mobile terminal's The Internet protocol address of each terminal in the home network is the same as the media access control address of the mobile agent (3, 8) in the new IP subnet. Bind, and set the properties of the geocoding protocol cache to static.

The method for realizing cross-Internet protocol internet travel of a mobile terminal according to any one of claims 1-4, characterized in that: the new IP subnet is a home network (1) refers to a mobile terminal

(5) From the foreign network (6) Just returned to the home network (1), the handover has not been completed.

6. The method for implementing mobile terminal cross-Internet protocol internet roaming according to any one of claims 1-4, characterized in that the new IP subnet is a foreign network (6) including mobile terminals (5) in different Foreign network roaming or from home network (1) to foreign network (6).

7. The method for realizing cross-Internet protocol internet travel of a mobile terminal according to one of claims 1-4, characterized in that said mobile terminal (5) is through the received mobile agent

(3, 8) uses the information in the proxy announcement to determine that it is roaming to a new IP subnet (1).

8. The method for implementing mobile terminal cross-Internet protocol internet roaming according to any one of claims 1-4, characterized in that the mobile terminal (5) obtains a mobile agent through a proxy announcement

(3, 8) Media Access Control Address (MAC-FA).

9. The method for realizing cross-Internet protocol internet roaming of a mobile terminal according to any one of claims 1-4, characterized in that: binding of Internet protocol addresses of each terminal in a home network of the mobile terminal (5) The subnet mask of the Internet protocol address of the home network (1) is used to calculate the Internet protocol address range of each terminal in the home network (1).

10. The method for implementing cross-Internet protocol internet roaming of a mobile terminal according to any one of claims 1-4, wherein the mobile terminal (5) is a mobile terminal using a windows 95/98 / ME operating system.