KR20090032474A - In-bound roaming system in mobile communication and method using the same - Google Patents

Abstract

An in-bound roaming system in mobile communication and a method thereof are provided to secure reliability of a network in a GSM/WCDMA packet network, thereby providing a normal roaming service even though malfunction occurs. A mobile communication terminal(100) produces a service request of a data call. A serving GPRS(General Packet Radio Service) support node(220) backs up an expired IP(Internet Protocol) address list by a shadow cache while deleting an expired IP(Internet Protocol) address list from a cache at every period. And the serving GPRS support node obtains a corresponding IP address about the service request. If the serving GPRS support node requests to inquire the IP address corresponding to the service request, a DNS(Domain Name Server) server(230) transmits the IP address to the serving GPRS support node by inquiring the IP address.

Description

In-bound roaming system in mobile communication and method using the same

The present invention relates to mobile communication technology, and more particularly to an inbound roaming system and method thereof in mobile communication.

In mobile communications, roaming services are intended to allow subscribers to use mobile communications services anywhere, across regions or borders. In particular, the international roaming service is an extension of this concept between countries, and means that subscribers can use mobile communication services in other countries through agreements between carriers in various countries. An inbound roaming service is a concept in which a foreigner uses a mobile communication service by using a network of a domestic telecommunication service provider that has entered a domestic contract with a foreign telecommunication service provider.

When inbound roaming service is provided in a domestic mobile communication network constructed with a Global System for Mobile (GSM) / Wideband Code Division Multiple Access (WCDMA) packet network, when an inbound roaming subscriber from overseas attempts to transmit a data call using a mobile terminal In addition, IP addresses of APNs (Access Point Names) of the mobile communication terminals are retrieved from DNS servers on domestic and international mobile communication networks, and data calls are processed using the retrieved IP addresses.

However, if the IP address is not normally looked up due to a DNS server or path problem, it takes a lot of time to perform normalization measures, and many data calls generated by inbound roaming subscribers are treated as failures during normalization. It is causing losses and customer complaints.

Therefore, there is an urgent need for fundamental measures to improve the quality of inbound roaming services.

Accordingly, an object of the present invention is to provide an inbound roaming system and a method for guaranteeing the reliability of a network in a GSM / WCDMA packet network to provide a normal roaming service even when a failure occurs.

Another technical problem to be achieved by the present invention is to provide an inbound roaming system and method for improving service quality.

Technical problems to be achieved by the present invention are not limited to the above-mentioned technical problems, and other technical problems not mentioned above may be clearly understood by those skilled in the art from the following description. There will be.

Inbound roaming system according to the present invention for achieving the above object, a mobile communication terminal for generating a service request of the data call; A serving GPRS that stores a list of IP addresses in an IP host table and a cache, and backs up a shadow cache while deleting a list of expired IP addresses from the cache at predetermined intervals, and obtains a target IP address for the service request. Support node; And a list of IP addresses stored in the cache, and when the serving GPRS support node requests an inquiry about the target IP address corresponding to the service request, the target IP address is queried and transmitted to the serving GPRS support node. It includes a DNS server.

On the other hand, inbound roaming method according to an aspect of the present invention, the step of storing the IP address list obtained from the DNS server in the cache; Periodically deleting, from the cache, the list of IP addresses whose validity period has elapsed among the list of IP addresses stored in the cache; Registering a list of IP addresses deleted from the cache as a shadow cache, and updating the shadow cache at every deletion period of the cache; And when a service request for a data call occurs, acquiring a target IP address for an access point name corresponding to the service request and performing data call processing.

Inbound roaming method according to another aspect of the present invention comprises the steps of: storing in the cache a list of IP addresses obtained from the DNS server; Periodically deleting, from the cache, the list of IP addresses whose validity period has elapsed among the list of IP addresses stored in the cache; Register the list of IP addresses deleted from the cache as a shadow cache, and at the time of registration, send a DNS query to the DNS server to update the list of registered IP addresses with the latest information, and update the shadow cache at every delete period of the cache. Making; And when a service request for a data call occurs, acquiring a target IP address for an access point name corresponding to the service request and performing data call processing.

The inbound roaming system and the method according to the present invention made as described above can guarantee the reliability of the network in the GSM / WCDMA packet network to provide a normal roaming service even in the event of a failure, and consequently can improve the quality of service.

Hereinafter, an inbound roaming system according to a preferred embodiment of the present invention will be described in detail with reference to FIGS. 1 and 2.

FIG. 1 is an overall configuration diagram of an inbound roaming system according to an embodiment of the present invention, and FIG. 2 is a partial configuration diagram of a serving GPRS support node (hereinafter referred to as 'SGSN') shown in FIG. 1.

1, an inbound roaming system according to an embodiment of the present invention implements a GSM / WCDMA packet network, and includes a mobile communication terminal 100, a base station 110 and a base station 110 connected to the mobile communication terminal 100. Radio access network (RAN) and a core network (CN).

The domestic mobile communication network 200 and the international mobile communication network 300 correspond to core networks, and each includes a plurality of SGSNs and a plurality of gateway GPRS support nodes (hereinafter referred to as 'GGSN'). . A plurality of SGSNs and GGSNs located on the domestic mobile communication network 200 and the international mobile communication network 300 perform mobility management and PDP context activation of the mobile communication terminal 100 and are responsible for transmitting and receiving packets.

Roaming service subscribers using the mobile communication terminal 100 are stored in a plurality of Internet servers (not shown) connected to the international mobile communication network 300 through the domestic mobile communication network 200 and the international mobile communication network 300. Data can be received.

The mobile communication terminal 100 is for providing a voice call and data communication service to a subscriber. When providing a data communication service, the mobile communication terminal 100 generates a service request of a general packet radio service (GPRS) and transmits it to the domestic mobile communication network 200 via the base station 110.

The Node B (Node B) 110 is a network termination device wirelessly connected to the mobile communication terminal 100, and receives a service request from the mobile communication terminal 100 and transmits the received service request to a wireless network. Send to the controller 210.

A radio network controller (RNC) 210 located in a transmission path interlocks a mobile communication terminal 100 with a domestic mobile communication network 200 to transmit a packet transmitted from a base station 110 to a domestic mobile communication network 200. Or a packet of the domestic mobile communication network 200 to the mobile communication terminal 100.

In the domestic mobile communication network 200, the SGSN 220 and the DNS server 230 is located.

SGSN 220 is a serving node of GPRS that is responsible for delivering packets sent to or directed to mobile communication terminal 100 within a service area of domestic mobile communication network 200. Responsible for the management of data communication services provided to the terminal 100, and transfers signals and traffic between the wireless network controller 210 and the GGSN 310.

That is, SGSN 220 performs functions such as routing and forwarding of packets, mobility management, logical link management, and authentication and billing, and IP (Internet) of GGSN 310 regarding access point name from DNS server 230. Protocol) Set the PDP context by obtaining the address.

Referring to FIG. 2, the SGSN 220 includes an IP host table 222, a cache 223, and a shadow cache 224 for querying an IP address, and includes an IP host table 222 and a cache 223. Save the list of IP addresses. Then, the cache server 223 backs up and stores the IP address list in which the valid time period (TTL: Time to Live) has elapsed from the cache 223 to the shadow cache 224, and obtains a target IP address for the service request. The valid period is set to a constant value (for example, 3 hours) according to the specification.

Domain name server (DNS) 230 provides a list of IP addresses stored in cache 223 at the request of SGSN 220, and SGSN 220 provides a list of destination IP addresses corresponding to the service request. When the inquiry is requested, the target IP address is queried from the upper DNS server 320 and transmitted to the SGSN 220.

In the international mobile communication network 300, the GGSN 310 and the upper DNS server 320 are located.

The GGSN 310 is directly connected to an internet network (not shown) and maintains routing information to the SGSN 220 to perform tunneling and IP routing functions. Here, the routing information is information for viewing a destination address among IP header contents of a packet to be transmitted and transmitting it to a desired SGSN / GGSN or an external network, and is a table generated by a routing protocol.

The packet transmitted from the SGSN 220 is converted into an appropriate packet data protocol (PDP) format through the GGSN 310 and sent to the Internet network. IP packets from the Internet go through the reverse process.

The upper DNS server 320 is connected to the DNS server 230 configured on the domestic mobile communication network 200 to periodically update the IP address list stored in the cache 223 in the DNS server 230.

In order to provide an inbound roaming service to the mobile communication terminal 100 in a roaming state, an interworking between the domestic mobile communication network 200 and the international mobile communication network 300 is required.

The PDP context must be activated in order for the mobile communication terminal 100 to be connected to the domestic mobile communication network 200 and the international mobile communication network 300 in response to the service request transmitted from the mobile communication terminal 100 of the subscriber.

The inbound roaming system processes the data call through the PDP context activation process. During the PDP context activation process, a series of procedures are required to activate the PDP, including proper subscriber authentication, access point name, and IP address assignment.

In order to transmit and receive a data call (packet) in response to a service request transmitted from the mobile communication terminal 100, a PDP context must be activated between the mobile communication terminal 100 and the GGSN 310.

The process of performing a data call connection between the mobile communication terminal 100 and the international mobile communication network 300 is briefly described as follows. Here, the data call connection process is a process of processing a data call with a PDP context activation process.

First, the subscriber selects an access point name corresponding to a desired service and inputs it to the mobile communication terminal 100. The mobile communication terminal 100 includes the input access point name in the PDP context activation request to the SGSN 220. send. At this time, security functions such as an authentication procedure and an encryption procedure are performed between the mobile communication terminal 100 and the SGSN 220. When such a procedure is completed, normal data communication services are performed between each other.

Accordingly, the SGSN 220 queries the IP host table 222 and the cache 223 for the connection point name included in the received PDP context activation request, queries the DNS server 230, or the shadow cache 224 in the shadow cache 224. The query finds the destination IP address of the GGSN 310 that is available.

Here, the process of determining the IP address of the GGSN 310 is a process of determining whether a target IP address of the available GGSN 310 exists, and if the target IP address is available as a result of the determination, the SGSN 220 displays the PDP. The context creation request is transmitted to the GGSN 310 on the corresponding international mobile communication network 300 to request the connection with the target IP address.

Then, the GGSN 310 generates a PDP context by receiving a PDP context creation request. At this time, if the PDP context is generated normally by determining whether the procedure is normally performed, the GGSN 310 notifies the SGSN 220 of the result using the PDP context creation response. Then, the SGSN 220 transmits the PDP context activation acceptance to the mobile communication terminal 100 so that the data communication service through the access point name input from the mobile communication terminal 100 can be started.

Referring to Figure 2, the detailed configuration of the SGSN 220 configured on the domestic mobile communication network 200 by way of example as follows.

As illustrated in FIG. 2, the SGSN 220 may include an IP host table 222, a cache 223, a shadow cache 224, a cache controller 221, and an IP translation. A unit 225 and a data call processing unit 228 are included.

If the destination IP address for the access point name of the data call originating from the mobile communication terminal 100 is not queried in the IP host table 222 and the cache 223, the SGSN 220 is sent from the mobile communication terminal 100. To query the destination IP address for the data point's access point name, send a DNS query and receive a DNS query response with the destination IP address in response.

In this case, a problem may occur in a multi-layered path such as a DNS server 230 on the domestic mobile communication network 200 or an upper DNS server 320 on the international mobile communication network 300, thereby causing a failure of the data call.

SGSN 220 utilizes shadow cache 224 as a backup space for roaming subscriber's IP address list, and target IP address within shadow cache 224 if a response to a DNS query was not sent as a problem on a multi-layered path. By completing the processing of the data call by inquiring, the situation in which the failure of the data call occurs due to a problem on the multi-layer path can be minimized.

IP host table 222 stores a list of IP addresses for domestic subscribers. Here, the IP address list includes a plurality of connection point names for data call processing and IP addresses for the plurality of connection point names.

The cache 223 stores a list of IP addresses obtained from the DNS server 230.

The shadow cache 224 backs up the list of IP addresses that are expired and deleted from the cache 223. Since the shadow cache 224 is utilized as a backup space, it is preferable to design a relatively large capacity compared to the cache 223.

The cache controller 221 may include its own timer to periodically delete a list of IP addresses whose validity period has elapsed from the cache 223 among the list of IP addresses stored in the cache 223, and shadow the list of IP addresses deleted from the cache. Register as 224, and update the shadow cache 224 for each erase cycle of the cache 223.

When the list of IP addresses deleted from the cache 223 is registered with the shadow cache 224, the cache controller 221 may store the list of IP addresses already stored in the shadow cache 224 among the list of IP addresses deleted from the cache 223. The list of IP addresses that are not updated and stored in the shadow cache 224 is newly registered in the shadow cache 224.

When the validity period has elapsed and the list of IP addresses deleted from the cache 223 is registered with the shadow cache 224, the cache controller 221 may update the list of IP addresses to be registered with the shadow cache 224 with the latest information. Can be.

In this case, the cache controller 221 registers the list of IP addresses deleted from the cache 223 as the shadow cache 224, but at the time of registration, the cache controller 221 sends a DNS query to the DNS server 230 to delete the IP from the cache 223. The address list is updated with the latest information and then registered in the shadow cache 224.

When the service call of the data call occurs, the IP conversion unit 225 obtains the target IP address of the GGSN 310 corresponding to the service request.

The IP conversion unit 225 includes an IP inquiry unit 226 and an IP query unit 227.

When the IP inquiry unit 226 receives the PDP context activation request including the access point name in response to the service request of the data call, the IP inquiry unit 226 searches the IP host table 222 and the cache 223 or the shadow cache 224 for the access point name. Inquires about the destination IP address.

When the target IP address is not queried by the IP query unit 226, the IP query unit 227 requests a query of the target IP address by sending a DNS query to the DNS server 230 and a DNS query from the DNS server 230. Obtain the target IP address by receiving the corresponding DNS query response. Then, the access point name included in the DNS query response and the target IP address for the access point name are stored as the IP address list of the cache 223.

The data call processor 228 activates the PDP context for the service request using the obtained target IP address, establishes a session, and performs data call processing.

As such, when the validity period of the IP addresses for the access point names in the cache 223 provided therein expires, the SGSN 220 moves the shadow list to the shadow cache 224 instead of deleting the corresponding IP address list completely. . Thereafter, if the DNS query response is not received due to a failure of the DNS server 230 or the upper DNS server 320 or a problem in the path, the target server may search for the target IP address for the corresponding access point name in the shadow cache 224. The target IP address of the GGSN 310 to process the call can be found to prevent roaming subscribers' data call failure.

Hereinafter, an inbound roaming method according to a preferred embodiment of the present invention will be described in detail with reference to FIGS. 3 to 6.

3 is a flowchart illustrating an inbound roaming method according to an exemplary embodiment of the present invention, and illustrates an inbound roaming method based on the SGSN 220.

First, in step S110, SGSN 220 has an IP host table 222 that stores a list of basic IP addresses for domestic subscribers, DNS in the process of processing data calls that are not queried in the IP host table 222 A list of IP addresses obtained from the server 230 is obtained and stored in the cache 223. Here, the IP address list is information including a plurality of connection point names from which the data call has been sent and IP addresses of the plurality of connection point names.

The size of the list of IP addresses that can be stored in the cache 223 is limited due to the limitations of the standard or its capacity. Therefore, the SGSN 220 inquires whether there is a list of IP addresses whose validity period has expired among the list of IP addresses stored in the cache 223 through steps S120 and S130, and checks the list of IP addresses whose validity period has passed. The operation of deleting from the cache 223 is repeated every fixed period (for example, three hours).

Next, in step S140, the SGSN 220 registers a list of IP addresses deleted from the cache 223 as the shadow cache 224. When the IP address list is deleted from the cache 223 and registered with the shadow cache 224, if the IP address list is registered without being updated with the latest information through a DNS query, the advantage of lowering the system load is that have.

This process is performed whenever the validity period elapsed IP address list is deleted from the cache 223, so that the shadow cache 224 is updated at each deletion period of the cache 223. At this time, the list of IP addresses already stored in the shadow cache 224 of the list of IP addresses deleted from the cache 223 is updated, and the list of IP addresses not stored in the shadow cache 224 is newly refreshed in the shadow cache 224. It is registered.

Next, the SGSN 220 detects whether a service request of a data call generated from the subscriber's mobile communication terminal 100 is received through step S150, and proceeds to step S160 when a service request including an access point name is received. .

Next, in step S160, SGSN 220 obtains the target IP address of the GGSN 310 of the mobile communication terminal 100 that transmitted the service request for data call processing.

Step S160 may be subdivided into steps S161 to S167.

First, in steps S161 and S162, the SGSN 220 inquires the target IP address of the GGSN 310 for the access point name to which the service request is transmitted from the IP host table 222 and the cache 223.

If no destination IP address is found in the IP host table 222 and cache 223 because there is no matching connection point name, the SGSN 220 proceeds to step S163 to the DNS server 230 for the destination IP address for the connection point name. Sends a DNS Query to request.

Thereafter, the SGSN 220 waits for a DNS Query Response in step S165, and if a response is not received after a predetermined time, the SGSN 220 proceeds to step S167 to query the shadow cache 224 to obtain a target IP address. Acquire.

When the DNS query response is received in step S165, the SGSN 220 proceeds to step S166 and matches the target IP address included in the received DNS query response with the corresponding access point name and stores it in the cache 223.

Next, in step S170, SGSN 220 performs a data call connection by activating the PDP context between the mobile communication terminal 100 and the GGSN 310 by using the target IP address of the GGSN 310 obtained through the step S160. .

FIG. 4 is a data flow diagram of some of the steps shown in FIG. 3, which illustrates steps S150 and S160 in more detail.

Steps S151 and S152 are steps for detecting a service request.

When a subscriber attempts to transmit a data call using a mobile communication terminal 100 capable of accessing a GSM / WCDMA packet network, the mobile communication terminal 100 transmits a service request to the SGSN 220. In addition, the mobile communication terminal 100 transmits an active PDP context request including an access point name from the mobile communication terminal 100 to the SGSN 220 together with a service request. Request activation of PDP context for data call processing.

The SGSN 220 receives an PDP context activation request including an access point name corresponding to a service request.

Steps S161 to S174 are steps of inquiring an IP address for the service request to perform data call processing.

In steps S161 to S166, the SGSN 220 queries the target IP address for the access point name from the IP host table 222, the cache 223, and the shadow cache 224, which are provided in itself, or from the DNS server 230. Obtain the target IP address.

Looking at this process in more detail as follows.

First, in steps S161 and S162, the SGSN 220 inquires a target IP address for the corresponding access point name from the IP host table 222 and the cache 223.

If the target IP address is not found because there is no matching connection point name, the SGSN 220 proceeds to step S163 and sends a DNS query to the DNS server 230 to request a target IP address inquiry. In operation S164, a DNS Query Response including the requested destination IP address is received from the DNS server 230.

In operation S165, when a DNS Query Response including a destination IP address is received from the DNS server 230, the SGSN 220 receives a DNS Query Response. ) Matches the target IP address with respect to the access point name and the access point name is stored in the cache 223.

If the search result is not received from the DNS server 230 until the predetermined waiting time passes (Timeout), the SGSN 220 proceeds to step S166 to query the target IP address from the shadow cache 224.

When the desired destination IP address is successfully queried in step S161, the SGSN 220 sends a DNS query to the DNS server 230 to receive / store the DNS query response in steps S163 to S165. There is no need to perform the step S166 of inquiring the shadow cache 224, and proceeds directly to step S171 for data call processing using the inquired target IP address.

Similarly, even when a DNS Query Response including a destination IP address is received through steps S163 to S165, since the shadow cache 224 does not need to be queried to obtain a destination IP address, step S166 is performed. It is omitted.

In addition, the SGSN 220 periodically monitors the DNS server 230 to detect a failure of the DNS server 230, a path failure, and performs steps S163 to S165 to perform a DNS query when a problem is detected. Omitted automatically, the data call processing may be performed with reference to the cache 223 and the shadow cache 224.

Steps S171 to S174 are subdivided into step S170.

In steps S171 to S174, the SGSN 220 activates the PDP context for the service request using the target IP address of the GGSN 310 to perform data call processing.

Looking at this process in more detail as follows.

First, in steps S171 and S172, the SGSN 220 establishes a packet exchange path between the mobile communication terminal 100 and the GGSN 310 and requests a creation of a PDP context from the GGSN 310 to assign an address. PDP Context Request) is sent. In response to this, a PDP context response is received from the GGSN 310.

Next, in step S173, a radio access bearer (RAB) for packet transmission is allocated between the SGSN 220, the radio network controller 210 (see FIG. 1), and the mobile communication terminal 100. . To this end, the SGSN 220 transmits a RAB Assignment Request to the radio network controller 210 and receives a RAB Assignment Response accordingly.

Next, in step S174, SGSN 220 transmits the PDP context activation (Active PDP Context Accept) to the mobile communication terminal 100 to perform a data call connection.

The GGSN 310 located on the international mobile communication network 300 periodically performs a step S180 to periodically update the IP address list in the DNS server 230 located in the domestic mobile communication network 200.

FIG. 5 is an overall flowchart of an inbound roaming method according to another exemplary embodiment of the present invention, and FIG. 6 is a detailed flowchart of some steps shown in FIG. 5 and illustrates the details of step S240.

Since the steps S210 to S230 and the steps S250 to S270 are the same as the steps S110 to S130 and S150 to S170 of FIG. 3, a detailed description thereof will be omitted.

In step S240, when the validity period has elapsed and the list of IP addresses deleted from the cache 223 is copied to the shadow cache 224, the list of IP addresses is updated with the latest information at the time of deletion and then copied to the shadow cache 224. do.

That is, the SGSN 220 registers the IP address list deleted from the cache 223 as the shadow cache 224 after a predetermined validity period, and at the time of registration, the DNSN 220 sends a DNS query to the DNS server 230 and a DNS query therefor. Receive a response to obtain the latest information of the IP address list. Then, the IP address list is updated using the obtained latest information and then stored in the shadow cache 224, and the shadow cache 224 is periodically updated by repeating this operation for each erase period of the cache 223. FIG.

In the inbound roaming method according to another embodiment of the present invention, when there is a list of IP addresses (specific access point names and IP addresses thereof) deleted from the cache 223, the DNS server for the access point names of the corresponding IP address lists at the time of deletion. After querying the IP address (230) to download a new latest IP address, the received latest IP address is stored in the shadow cache 224, so that the new IP address can be stored / used in comparison with the exemplary embodiment.

Referring to Figure 6, the step S240 is described in more detail as follows.

First, in step S241, SGSN 220 generates a DNS query for the list of IP addresses that are deleted from the cache 223 after the validity period has elapsed.

Next, in steps S242 and S243, the SGSN 220 transmits the generated DNS query to the DNS server 230 and receives a DNS query response to the DNS query transmitted from the DNS server 230.

In step S244, when the DNS query response is received from the DNS server 230, the SGSN 220 uses the list of IP addresses included in the received DNS query response to update the IP address list deleted from the cache 223 as the latest information. Update

Next, in step S245, SGSN 220 registers the list of IP addresses updated with the latest information into the shadow cache 224.

In step S243, if the DNS query response is not received even after a predetermined waiting time, the list of IP addresses deleted from the cache 223 is not updated with the latest information and is registered in the shadow cache 224 as it is.

In step S246, the SGSN 220 performs the steps S241 to S245 for each deletion period of the cache 223 while generating, transmitting, receiving a DNS query response, and a list of IP addresses deleted from the cache 223. The steps of updating and registering with information are repeated.

Although embodiments of the present invention have been described above with reference to the accompanying drawings, those skilled in the art to which the present invention pertains may implement the present invention in other specific forms without changing the technical spirit or essential features thereof. I can understand that.

Therefore, since the embodiments described above are provided to completely inform the scope of the invention to those skilled in the art, it should be understood that they are exemplary in all respects and not limited. The invention is only defined by the scope of the claims.

The inbound roaming system and its method according to the present invention can guarantee the reliability of the network in the GSM / WCDMA packet network to provide a normal roaming service even in the event of a failure, as a result can improve the quality of service of the roaming service.

1 is an overall configuration diagram of an inbound roaming system according to an embodiment of the present invention.

2 is a partial configuration diagram of the serving GPRS support node shown in FIG. 1;

3 is an overall flow diagram of an inbound roaming method according to an embodiment of the present invention.

4 is a data flow diagram of some of the steps shown in FIG.

5 is an overall flow diagram of an inbound roaming method according to another embodiment of the present invention.

6 is a detailed flowchart of some of the steps shown in FIG.

*** Explanation of symbols for the main parts of the drawing ***

100: mobile communication terminal 110: base station

200: domestic mobile network 210: wireless network controller

220: serving GPRS support node 230: DNS server

300: international mobile communication network 310: gateway GPRS support node

320: parent DNS server

Claims (16)

A mobile communication terminal for generating a service request of a data call; A serving GPRS that stores a list of IP addresses in an IP host table and a cache, and backs up a shadow cache while deleting a list of expired IP addresses from the cache at predetermined intervals, and obtains a target IP address for the service request. Support node; And Providing a list of IP addresses stored in the cache, and when the serving GPRS support node requests an inquiry about the target IP address corresponding to the service request, the target IP address is queried and transmitted to the serving GPRS support node. DNS server Inbound roaming system comprising a. The method of claim 1, wherein the serving GPRS support node, An IP host table for storing a list of IP addresses for domestic subscribers; A cache for storing a list of IP addresses obtained from the DNS server; A shadow cache for backing up and storing a list of IP addresses that are expired and deleted from the cache; Periodically, the list of IP addresses expired from the list of IP addresses stored in the cache is periodically deleted from the cache, the list of IP addresses deleted from the cache is registered as the shadow cache, and the shadow cache is deleted at each cache deletion period. A cache controller for updating the cache; An IP conversion unit for obtaining a target IP address for an access point name corresponding to the service request when a service request of a data call occurs; And Data call processing unit for performing data call processing by activating the PDP context for the service request using the target IP address Inbound roaming system comprising a. The method of claim 2, wherein the data call processing unit, When the PDP context activation request including the access point name corresponding to the service request of the data call is received, an IP inquiry unit for searching the IP host table and the cache or the shadow cache to query the target IP address for the access point name ; And If the target IP address is not queried, a DNS query is sent to the DNS server to request the query of the target IP address, and a DNS query response corresponding to the DNS query is received from the DNS server to obtain the target IP address. An IP query unit for storing the access point name and the target IP address of the access point name included in the DNS query response into the cache; Inbound roaming system comprising a. The method of claim 2, wherein the cache control unit, When registering a list of IP addresses deleted from the cache into the shadow cache, the list of IP addresses already stored in the shadow cache among the list of IP addresses deleted from the cache is updated, and the list of IP addresses not stored in the shadow cache is updated. Inbound roaming system, characterized in that the new registration. The method of claim 2, wherein the cache control unit, Registering a list of IP addresses deleted from the cache as a shadow cache, and sending a DNS query to the DNS server at the time of registration to update the registered list of IP addresses with the latest information. The method of claim 1, And an upper DNS server that periodically updates a list of IP addresses stored in the DNS server. The method of claim 1, wherein the IP address list, An inbound roaming system comprising a plurality of access point names and IP addresses for the plurality of access point names. Storing a list of IP addresses obtained from a DNS server in a cache; Periodically deleting a list of IP addresses whose validity period has elapsed from the list of IP addresses stored in the cache from the cache; Registering a list of IP addresses deleted from the cache as a shadow cache, and updating the shadow cache at every deletion period of the cache; And When a service request for a data call occurs, acquiring a target IP address corresponding to an access point name corresponding to the service request and performing data call processing. Inbound roaming method comprising a. The method of claim 8, wherein the performing of the data call processing comprises: Receiving a PDP context activation request including an access point name corresponding to the service request of the data call; Obtaining the target IP address for the access point name from the IP host table, the cache, or the DNS server, or the shadow cache; And Activating a PDP context for the service request using the destination IP address to perform data call processing Inbound roaming method comprising a. The method of claim 9, wherein the obtaining of the target IP address comprises: Querying the target IP address from the IP host table and the cache; If the target IP address is not queried, sending a DNS query to the DNS server to request the target IP address to be queried; When the DNS query response corresponding to the DNS query is received from the DNS server, storing the access point name included in the DNS query response and the target IP address for the access point name in the cache; And If the query result is not received from the DNS server, retrieving the target IP address from the shadow cache Inbound roaming method comprising a. The method of claim 9, wherein the receiving of the PDP context activation request comprises: Attempting a service request of a data call in a mobile communication terminal; And Transmitting, by the mobile communication terminal, the PDP context activation request including the access point name in response to the service request Inbound roaming method comprising a. The method of claim 8, wherein the IP address list, An inbound roaming method comprising a plurality of access point names and IP addresses for the plurality of access point names. The method of claim 8, wherein in the registering and updating of the IP address list deleted from the cache, The list of IP addresses deleted from the cache, the list of IP addresses already stored in the shadow cache is updated, and the list of IP addresses not stored in the shadow cache is newly registered. The method of claim 8, The upper DNS server periodically updates the list of IP addresses stored in the DNS server. Storing a list of IP addresses obtained from a DNS server in a cache; Periodically deleting, from the cache, the list of IP addresses whose validity period has elapsed among the list of IP addresses stored in the cache; Register the list of IP addresses deleted from the cache as a shadow cache, and at the time of registration, send a DNS query to the DNS server to update the list of registered IP addresses with the latest information, and update the shadow cache at every delete period of the cache. Making; And When a service request for a data call occurs, acquiring a target IP address corresponding to an access point name corresponding to the service request and performing data call processing. Inbound roaming method comprising a. The method of claim 15, wherein registering and updating the list of IP addresses to be deleted from the cache, Generating a DNS query for the list of IP addresses to be deleted from the cache; Sending the DNS query to the DNS server; Receiving a DNS query response to the DNS query from the DNS server; Updating the list of IP addresses deleted from the cache with the latest information by using the list of IP addresses included in the DNS query response; Registering the list of IP addresses updated with the latest information into the shadow cache; And Generating, transmitting, receiving the DNS query response, and updating and registering the list of IP addresses deleted from the cache with the latest information at each period of the cache deletion. Inbound roaming method comprising a.

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