WO2020261458A1 - Communication system, communication method, communication control device, communication control method, relay device, relay method, and program - Google Patents

Abstract

This communication control device enables reduction of communication delay in roaming communication. This communication control device is for managing a roaming communication session regarding a communication terminal, and is included in a home network of the communication terminal connected in a communicable manner to a visited network accessed by the communication terminal. The communication control device stores network identification information and one of a plurality of relay devices in association with each other, receives a session generation request that is regarding the communication terminal and that includes the network identification information of the visited network, transmits, to one of the plurality of relay devices, a session establishment request that is regarding the communication terminal and that is for allowing the relay device to relay communication between the communication terminal and a packet data network, and specifies, as a relay device to which the session establishment request is transmitted, the relay device associated with the network identification information of the visited network included in the session generation request.

Description

Communication system, communication method, communication control device, communication control method, relay device, relay method and program

The present disclosure relates to communication systems, communication methods, communication control devices, communication control methods, relay devices, relay methods and programs.

Conventionally, various operators have operated mobile communication systems such as the 4th generation mobile communication system (4G). 4G is composed of access networks such as LTE (Long Term Evolution) and EPC (Evolved Packet Core). By contracting with one of these operators, the user of the mobile communication terminal (UE) connects the UE to the PDN (Packet Data Network) via the network operated by the operator and uses various communication services. be able to.

In addition, the user can use a network operated by another operator that interconnects (roaming connection) with the network of the operator (home operator) contracted by the user. As a result, the user can use various communication services via the network even if the contracted operator operates the network in a different area from the area where another operator (visited operator) operates the network. Can be used.

Non-Patent Document 1 discloses the configuration of interconnection in 4G, and Non-Patent Document 2 discloses the configuration of interconnection in the 5th generation mobile communication system (5G).

In conventional roaming communication, the UE connects to the PDN via the visitor's network and the home operator's network. That is, since the data transmitted and received between the UE and the PDN all pass through the line connecting the home operator's network and the visited operator's network, the communication delay increases.

The purpose of the communication system, communication method, communication control device, communication control method, relay device, relay method and program is to make it possible to reduce the communication delay of roaming communication.

The communication system according to the embodiment is a communication control device and roaming that manages a roaming communication session for a communication terminal included in the home network of the communication terminal, which is communicably connected to the visited network accessed by the communication terminal. A communication system including a plurality of relay devices for relaying communication, the communication control device is a storage unit that stores network identification information in association with any of the relay devices, and a visited network. Establishing to send a session establishment request for a communication terminal to a generation request receiving unit that receives a session generation request for a communication terminal and one of a plurality of relay devices including the network identification information of Each of the plurality of relay devices includes a request transmitter and relays communication between the communication terminal and the packet data network based on the received session establishment request when the session establishment request is received. A processing unit is provided, and the establishment request transmission unit is characterized in that the relay device associated with the network identification information included in the session generation request is specified as the relay device for transmitting the session establishment request.

The packet data network may be an IP service network different from the home network and the visited network. The packet data network may be operated by a home operator or a visited operator, or may be a network operated by another operator. Further, the packet data network may include a plurality of networks.

The communication system according to the embodiment further includes a policy information management device that stores a plurality of policy information regarding priority control or billing conditions for a plurality of communication terminals, and the communication control device is attached to the communication terminal based on a session generation request. It also has an acquisition unit that acquires the associated policy information from the policy information management device, the establishment request transmission unit sends a session establishment request that includes the acquired policy information, and the relay processing unit sends the policy included in the session establishment request. It is preferable to relay the communication based on the information.

The communication system according to the embodiment further includes an identification information transmission device included in the home network and a second communication control device that manages a session of non-roaming communication, and the identification information transmission device receives and transmits an identification information transmission request. When the request receiver and the received identification information transmission request are the identification information transmission requests transmitted from the visited network, the identification information of the communication control device is transmitted to the visited network, and the received identification information transmission request is the home. When the identification information transmission request is transmitted from the network, it is preferable to include an identification information transmission unit that transmits the identification information of the second communication control device to the home network.

In the communication system according to the embodiment, it is preferable that the network identification information is a PLMN (Public Land Mobile Network) number.

In the communication system according to the embodiment, the storage unit further stores the area information for identifying the area in the network shown in the network identification information in association with any one of the plurality of relay devices, and stores the establishment request transmission unit. Preferably identifies the relay device associated with the area information of the area where the communication terminal is located in the visited network shown in the network identification information included in the session generation request as the relay device for transmitting the session establishment request. ..

In the communication system according to the embodiment, it is preferable that the area information is TAC (Tracking Area Code).

In the communication system according to the embodiment, it is preferable that the communication control device is PGW (Packet Data Network Gateway) -C (Control Plane) and the relay device is PGW-U (User Plane).

In the communication system according to the embodiment, it is preferable that the communication control device is an SMF (Session Management Function) and the relay device is an UPF (User Plane Function).

In the communication system according to the embodiment, the communication control device is installed in the country of the second country where the home network is operated, which is different from the first country where the visited network is operated, and the relay device is the first country. It is preferable that it is installed in Japan.

In the communication system according to the embodiment, the communication control device is installed in the country of the second country where the home network is operated, which is different from the first country where the visited network is operated, and the relay device is the first country. And it is preferable that it is installed in a country different from the second country.

The communication method according to the embodiment is a communication control device and roaming that manage a roaming communication session for the communication terminal included in the home network of the communication terminal, which is communicably connected to the visited network accessed by the communication terminal. A communication method using a communication system including a plurality of relay devices for relaying communication, in which a communication control device associates and stores network identification information with one of the plurality of relay devices, and stores the visit network. Receives a session generation request for a communication terminal including the network identification information of, and sends a session establishment request for a communication terminal to any of the relay devices of the plurality of relay devices. When each receives a session establishment request, the session in transmitting the session establishment request includes relaying the communication between the communication terminal and the packet data network based on the received communication session establishment request. The relay device associated with the network identification information included in the generation request is specified as the relay device for transmitting the session establishment request.

The communication control device according to the embodiment is a communication control device that manages a roaming communication session about the communication terminal included in the home network of the communication terminal, which is communicably connected to the visited network accessed by the communication terminal. A communication control device for a communication system including a plurality of relay devices for relaying roaming communication, a storage unit for storing network identification information in association with any of the relay devices, and a visited network. For the generation request receiving unit that receives the session generation request for the communication terminal including the network identification information of the above, and for any of the relay devices of the plurality of relay devices, the relay device for the communication terminal is the communication terminal. It includes an establishment request transmitter that transmits a session establishment request for relaying communication with the packet data network, and the establishment request transmitter uses the network identification information of the visited network included in the session generation request. It is characterized in that the associated relay device is specified as a relay device that transmits a session establishment request.

The communication control method according to the embodiment includes a communication control device that manages a roaming communication session for a communication terminal, which is included in the home network of the communication terminal and is communicably connected to a visited network accessed by the communication terminal. A communication control method using a communication control device of a communication system including a plurality of relay devices for relaying roaming communication, in which network identification information is stored in association with any of the multiple relay devices, and is visited. The session generation request for the communication terminal including the network identification information of the network is received, and the relay device for the communication terminal is the communication terminal and the packet data for any of the relay devices. In sending a session establishment request, including sending a session establishment request for relaying communication with the network, the relay device associated with the network identification information of the visited network included in the session generation request is sessioned. It is characterized in that it is specified as a relay device for transmitting an establishment request.

The program according to the embodiment is a communication control device and roaming communication that manages a roaming communication session for a communication terminal included in the home network of the communication terminal, which is communicably connected to the visited network accessed by the communication terminal. It is a program of a communication control device of a communication system including a plurality of relay devices for relaying a network identification information and stores the network identification information in association with any one of the multiple relay devices to identify the network of a visited network. A session generation request for a communication terminal including information is received, and for any of the relay devices, the relay device for the communication terminal is between the communication terminal and the packet data network. The communication control device is made to execute the session establishment request for relaying the communication of, and in the transmission of the session establishment request, the relay device associated with the network identification information of the visited network included in the session generation request is transmitted. It is characterized in that it is specified as a relay device that transmits a session establishment request.

The relay device according to the embodiment is a communication control device and roaming that manage a roaming communication session about the communication terminal included in the home network of the communication terminal, which is communicably connected to the visited network accessed by the communication terminal. A relay device for a communication system including a plurality of relay devices for relaying communication, and the communication control device transmits to the relay device associated with the network identification information of the visited network included in the session generation request for the communication terminal. When the received session establishment request is received, the relay processing unit that relays the communication between the communication terminal and the packet data network is provided based on the received session establishment request.

The relay method according to the embodiment is a communication control device and roaming that manages a roaming communication session for a communication terminal included in the home network of the communication terminal, which is communicably connected to the visited network accessed by the communication terminal. A relay method using a relay device of a communication system including a plurality of relay devices for relaying communication, in which the communication control device is associated with the network identification information of the visited network included in the session generation request for the communication terminal. When the session establishment request transmitted to the communication terminal is received, the communication between the communication terminal and the packet data network is relayed based on the received session establishment request.

The program according to the embodiment is a communication control device and roaming communication that manages a roaming communication session for a communication terminal included in the home network of the communication terminal, which is communicably connected to the visited network accessed by the communication terminal. A program for a relay device of a communication system including a plurality of relay devices for relaying the above, and the communication control device is for a relay device associated with network identification information of a visited network included in a session generation request for a communication terminal. When the transmitted session establishment request is received, the relay device is made to relay the communication between the communication terminal and the packet data network based on the received session establishment request.

According to the embodiment, the communication system, the communication method, the communication control device, the communication control method, the relay device, the relay method and the program make it possible to reduce the communication delay of the roaming communication.

The object and effect of the present invention will be recognized and obtained, especially by using the components and combinations pointed out in the claims. Both the general description described above and the detailed description below are exemplary and descriptive and do not limit the invention as described in the claims.

It is a schematic diagram for demonstrating the outline of embodiment. It is a schematic diagram for demonstrating the outline of embodiment. It is a figure which shows an example of the schematic structure of the roaming communication system 1. It is a figure which shows an example of the schematic structure of PGW-C28. It is a figure which shows an example of the schematic structure of PGW-U41. It is a figure which shows an example of the schematic structure of A-DNS25. It is a figure which shows an example of the data structure of the identification information table T1. It is a figure which shows an example of the data structure of the DNS table T2. It is a sequence diagram which shows an example of the processing flow by a roaming communication system 1. It is a flow figure which shows an example of the flow of the identification information transmission processing. It is a figure which shows an example of the schematic structure of the roaming communication system 2.

Hereinafter, various embodiments will be described with reference to the drawings. However, it should be noted that the scope of the present disclosure is not limited to the following embodiments, but extends to the inventions described in the claims and their equivalents.

1 and 2 are schematic views for explaining the outline of the embodiment. FIG. 1 shows an outline of a conventional roaming communication system, and FIG. 2 shows an outline of a roaming communication system according to an embodiment. In addition, in FIG. 1 and FIG. 2, only the minimum configuration necessary for explanation is shown.

First, the conventional roaming communication system 100 will be described with reference to FIG. The conventional roaming communication system 100 has a UE 150, a VPLMN (Visited Public Land Mobile Network) 110, an HPLMN (Home Public Land Mobile Network) 120, a PDN 130, and an IPX (IP Exchange) 140. The VPLMN110 is a network operated by a visited operator in a first country where the user of the UE 150 stays. HPLMN120 is a network operated by home operators in a second country. The PDN 130 is a network outside the operator's network, such as the Internet. The IPX140 is a relay station for interconnecting networks of different operators. The VPLMN 110 and the HPLMN 120 are interconnected at the IPX 140 so that roaming communication is possible. The VPLMN 110 and the HPLMN 120 may be interconnected by a plurality of IPX140s.

The HPLMN 120 has a PGW (Packet Data Network Gateway) 121. The PGW 121 is a gateway device that manages communication sessions and relays communication between the inside of the operator's network and the PDN 130.

In the following, in the conventional roaming communication system 100, the procedure in which the UE 150 in the first country communicates with the PDN 130 will be described.

First, the UE 150 transmits a connection request to the VPLMN110. Upon receiving the connection request, the VPLMN 110 acquires the subscriber information of the user of the UE 150 from the HPLMN 120. When the subscriber information is acquired, the VPLMN 110 transmits a session generation request for the UE 150 to the PGW 121 of the HPLMN 120. Upon receiving the session generation request, the PGW 121 generates a communication session for the UE 150. This enables roaming communication between the UE 150 and the PDN 130.

Communication between the UE 150 and PDN 130 in the first country is relayed to the PGW 121 of the HPLMN 120 in the second country via the VPLMN 110. That is, the data transmitted and received between the UE 150 and the PDN 130 all pass through the line connecting the VPLMN 110 and the HPLMN 120. In general, roaming communication occurs when the UE moves to a different country or region, so these networks are often geographically or network topologically separated. Therefore, when passing through the lines connecting these networks, the time for physically transmitting the communication-related signal increases, and the communication delay increases because many devices process the communication-related data packets. To do.

Subsequently, the roaming communication system 1 according to the embodiment will be described with reference to FIG. The roaming communication system 1 has a UE 50, a VPLMN 10, an HPLMN 20, a PDN 30, and a plurality of IPX40s. The VPLMN10 is an example of a visited network, and the HPLMN20 is an example of a home network. The PDN30 is an example of a packet data network. The UE 50 is an example of a communication terminal.

As a difference from FIG. 1, the roaming communication system 1 according to the embodiment has a PGW-C (Control Plane) 28 and a plurality of PGW-U (User Planes) 41a and 41b instead of the PGW. Among the functions of PGW, PGW-C28 includes functions related to a control plane such as managing communication sessions. Further, the PGW-C28 stores a plurality of network identification information in association with the PGW-U. The PGW-U41 is a device having a user plane-related function such as relaying communication between the UE 50 and the PDN 30 among the functions of the PGW. That is, PGW-C28 and PGW-U41 realize the same functions as the conventional PGW 121 by combining them. The PGW-C28 is an example of a communication control device, and the PGW-U41 is an example of a relay device.

PGW-C28 is included in HPLMN20. Each of the plurality of PGW-U41s is communicably connected to the PGW-C28, and in combination with the PGW-C28, the HPLMN20 functions as a PGW. That is, the plurality of PGW-U41s are owned or managed by the operator of HPLMN20. Each of the plurality of PGW-U41 is included in any of the plurality of IPX40s. The plurality of IPX40s are provided, for example, in a country or region different from the second country in which HPLMN20 is operated. Any of the plurality of IPX40s may be provided in the first country. The fact that PGW-U41 is included in IPX40 means that, for example, PGW-U41 is installed inside IPX40, which is a relay station.

The outline of the processing until the UE 50 performs roaming communication in the roaming communication system 1 will be described below.

First, the UE 50 transmits a connection request to the VPLMN 10. Upon receiving the connection request, the VPLMN 10 acquires the subscriber information of the user of the UE 50 from the HPLMN 20. When the subscriber information is acquired, the VPLMN 10 transmits a session generation request for the UE 50 to the PGW-C28 of the HPLMN 20 ((1) in FIG. 2). Upon receiving the session generation request, the PGW-C28 transmits the session establishment request to the PGW-U41 associated with the network identification information included in the session generation request ((2) in FIG. 2). Upon receiving the session establishment request, PGW-U41 establishes a communication session for the UE 50. This enables roaming communication between the UE 50 and the PDN 30. The communication between the UE 50 and the PDN 30 is relayed by the PGW-U41 included in the IPX40 ((3) in FIG. 2).

As described above, in the roaming communication system 1 according to the embodiment, the PGW-C28 identifies the PGW-U41 associated with the network identification information included in the session generation request, and the identified PGW-U41 is the UE 50. The communication with the PDN30 is relayed. By doing so, the roaming communication system according to the present invention makes it possible to reduce the communication delay of roaming communication. That is, in the roaming communication system 1 according to the embodiment, the communication between the UE 50 and the PDN 30 is relayed by the PGW-U41 included in the IPX 40 without going through the HPLMN 20. Then, the PGW-C28 can identify the PGW-U41 included in the IPX40 geographically or network topologically close to the VPLMN10 as the PGW-U that relays the communication. As a result, the roaming communication system 1 according to the embodiment can reduce the transmission time of the signal related to communication and the processing time of the data packet related to communication. Then, the roaming communication system 1 makes it possible to reduce the communication delay as compared with the conventional roaming communication system in which the PGW included in the HPLMN 20 relays the communication. Further, the roaming communication system 1 makes it possible to suppress deterioration of communication quality due to loss of the transmission line or the like and improve communication quality by shortening the transmission path through which the data packet related to communication passes. The IPX40 geographically or network topologically close to the VPLMN10 means, for example, an IPX40 located in the first country where the VPLMN10 is operated, or in another country located in the vicinity of the first country. ..

The above explanation is merely an explanation for deepening the understanding of the contents of the present invention. Specifically, the present invention may be carried out in each of the embodiments described below, and may be carried out by various modifications without substantially exceeding the principles of the present invention. All such variations are included within the scope of the present invention and the present specification.

FIG. 3 is a diagram showing an example of a schematic configuration of the roaming communication system 1 according to the embodiment. The roaming communication system 1 includes a VPLMN10, an HPLMN20, a PDN30, an IPX40, a first UE50, and a second UE60. The first UE 50 and the second UE 60 are both UEs of users who have contracted with a home operator who operates HPLMN 20. The first UE 50 is a roaming terminal that accesses the VPLMN 10, and the second UE 60 is a non-roaming terminal that accesses the HPLMN 20.

VPLMN10 includes V-eNB 11, V-SGW (Serving Gateway) 12, V-MME (Mobility Management Entity) 13, and V-DNS (Domain Name System) 14. The V-eNB 11, V-SGW 12, V-MME 13 and V-DNS 14 are installed, for example, in the first country where VPLMN10 is operated.

The V-eNB 11 is an LTE base station, and transmits / receives data to / from the first UE 50 by wireless communication. The V-SGW 12 is a gateway device for connecting the first UE 50 that communicates with the V-eNB 11 to the EPC of the VPLMN 10. The V-MME 13 is a device that manages the mobility of the first UE 50 and manages the communication session. The V-MME 13 receives the connection request transmitted from the first UE 50 and acquires the subscriber information of the user of the first UE 50. The V-DNS14 is a so-called DNS server that receives a request for resolving a host name and transmits identification information (IP address) of a device corresponding to the host name.

HPLMN20 includes H-eNB21, H-SGW22, H-MME23, H-DNS24, A (Authoritative) -DNS25, HSS (Home Subscriber Server) 26, PGW27, PGW-C28 and PCRF (Policy and Charging Rules Function) 29. Including. H-eNB21, H-SGW22, H-MME23 and H-DNS24 have the same configurations as V-eNB21, V-SGW22, V-MME23 and V-DNS24, respectively. H-eNB21, H-SGW22, H-MME23, H-DNS24, A-DNS25, HSS26, PGW27, PGW-C28 and PCRF29 are installed in, for example, a second country where HPLMN20 is operated.

A-DNS25 is an authoritative DNS server of HPLMN20. The A-DNS25 stores the host name of the device included in the HPLMN 20 in association with the identification information, and when a host name resolution request is received from the V-DNS14 or the H-DNS24, the device corresponding to the host name. Identification information (IP address) of. In particular, when the A-DNS25 receives an APN (Access Point Name) resolution request, it transmits the identification information of the PGW 27 or PGW-C28 corresponding to the APN. The A-DNS25 is an example of an identification information transmitting device.

HSS26 is a server that registers the location and manages subscriber information, authentication information, and the like. The HSS 26 transmits the subscriber information of the user of the first UE 50 in response to the request from the V-MME 13 that has received the registration request from the first UE 50. Further, the HSS 26 transmits the subscriber information of the user of the second UE 60 in response to the request from the H-MME 23 that has received the registration request from the second UE 60.

PGW27 is a gateway device that manages communication sessions and relays communication between the inside of HPLMN20 and PDN3. Further, the PGW-C28 is a device having a function related to a control plane among the functions of the PGW. In an embodiment, the PGW 27 manages a non-roaming communication session of the second UE 60 (ie, a non-roaming terminal) and relays communication between the second UE 60 and the PDN 30. Further, the PGW-C28 manages a roaming communication session of the first UE 50 (that is, a roaming terminal). The PGW 27 is an example of the second communication control device.

PCRF29 is a server that manages policy information related to priority control or billing conditions. The PCRF 29 stores policy information about a plurality of UEs. When the PCRF29 receives the policy information transmission request from PGW27 or PGW-C28, the PCRF29 transmits the policy information to the PGW27 or PGW-C28. The PCRF29 is an example of a policy information management device.

IPX40 has a plurality of PGW-U41a to 41c (hereinafter, collectively referred to as PGW-U41 when it is not necessary to distinguish them). In FIG. 3, a plurality of PGW-U41s are arranged in one IPX, but a plurality of PGW-U41s may be dispersedly arranged in a plurality of IPX40s different from each other. The plurality of IPX40s may be located in a country different from the first and second countries, or may be located in the first country. That is, the PGW-U41 may be installed in the country of the first country, or may be installed in the country different from the first country and the second country.

PGW-U41 is a device having a user plane function among the functions of PGW. The PGW-U41 relays communication between the V-SGW 11 and the PDN3. The PGW-U41 is owned and managed by a home operator and is communicably connected to the PGW-C28 of the HPLMN 20. That is, when the IPX40 is operated by a business operator different from the home operator, the PGW-U41 is installed by the home operator by collocation at the IPX40.

Note that PGW-U41 may be included in VPLMN10 instead of IPX40. That is, the PGW-U41 may be installed by the home operator in the VPLMN 10 by collocation. By doing so, the first UE 50 and the PGW-U41 are closer to each other geographically or in terms of network topology, and the communication delay of roaming communication is further reduced.

FIG. 4 is a diagram showing an example of a schematic configuration of PGW-C28. The PGW-C28 includes a first storage unit 281, a first communication unit 282, and a first processing unit 283.

The first storage unit 281 is a device for storing a program or data, for example, a semiconductor memory device. The first storage unit 281 stores an operating system program, a driver program, an application program, data, and the like used for processing by the first processing unit 283. The program is installed in the first storage unit 281 from a computer-readable portable storage medium such as a CD-ROM or a DVD-ROM using a known setup program or the like.

The first communication unit 282 includes a communication interface circuit that enables the PGW-C28 to communicate with other devices via a network. The communication interface circuit included in the first communication unit 282 is a wired LAN (Local Area Network) communication interface circuit or the like. The first communication unit 282 transmits the data supplied from the first processing unit 283 to another device, and supplies the data received from the other device to the first processing unit 283.

The first processing unit 283 includes one or more processors and peripheral circuits thereof. The first processing unit 283 is, for example, a CPU (Central Processing Unit), and controls the operation of the PGW-C28 in an integrated manner. The first processing unit 283 may be a DSP (Digital Signal Processor), an LSI (Large-Scaled IC), an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or the like. The first processing unit 283 controls the operation of the first communication unit 282 so that various processes of the PGW-C28 are executed in an appropriate procedure based on the program stored in the first storage unit 281. The first processing unit 283 executes processing based on the program stored in the first storage unit 281. In addition, the first processing unit 283 can execute a plurality of programs in parallel.

The first processing unit 283 includes a generation request receiving unit 284, an acquisition unit 285, and an establishment request transmitting unit 286. Each of these parts is a functional block realized by a program executed by the first processing unit 283. Each of these parts may be realized by a program executed on a VM (Virtual Machine) realized by a program executed by the first processing unit 283. Further, each of these parts may be mounted on the PGW-C28 as firmware.

FIG. 5 is a diagram showing an example of a schematic configuration of PGW-U41. The PGW-U41 includes a second storage unit 411, a second communication unit 412, and a second processing unit 413.

The second storage unit 411 is a device for storing a program or data, for example, a semiconductor memory device. The second storage unit 411 stores programs, data, and the like used for processing by the second processing unit 413. The program is installed in the second storage unit 411 from a computer-readable portable storage medium such as a CD-ROM or a DVD-ROM using a known setup program or the like.

The second communication unit 412 includes a communication interface circuit that enables the PGW-U41 to communicate with other devices via a network. The second communication unit 412 transmits the data supplied from the second processing unit 413 to another device, and supplies the data received from the other device to the second processing unit 413.

The second processing unit 413 includes one or more processors and their peripheral circuits. The second processing unit 413 comprehensively controls the operation of the PGW-U41. The second processing unit 413 may be a DSP, LSI, ASIC, FPGA or the like. The second processing unit 413 controls the operation of the second communication unit 412 so that various processes of the PGW-U41 are executed in an appropriate procedure based on the program stored in the second storage unit 411. The second processing unit 413 executes processing based on the program stored in the second storage unit 411.

The second processing unit 413 includes an establishment response transmission unit 414 and a relay processing unit 415. Each of these parts is a functional block realized by a program executed by the second processing unit 413. Each of these parts may be realized by a program executed on the VM realized by the program executed by the second processing unit 413. Further, each of these parts may be mounted on the PGW-U41 as firmware.

FIG. 6 is a diagram showing an example of a schematic configuration of A-DNS25. The A-DNS 25 includes a third storage unit 251, a third communication unit 252, and a third processing unit 253.

The third storage unit 251 is a device for storing a program or data, for example, a semiconductor memory device. The third storage unit 251 stores programs, data, and the like used for processing by the third processing unit 253. The program is installed in the third storage unit 251 from a computer-readable portable storage medium such as a CD-ROM or a DVD-ROM using a known setup program or the like.

The third communication unit 252 includes a communication interface circuit that enables the A-DNS25 to communicate with other devices via a network. The third communication unit 252 transmits the data supplied from the third processing unit 253 to another device, and supplies the data received from the other device to the third processing unit 253.

The third processing unit 253 includes one or more processors and their peripheral circuits. The third processing unit 253 comprehensively controls the operation of the A-DNS 25. The third processing unit 253 may be a DSP, LSI, ASIC, FPGA or the like. The third processing unit 253 controls the operation of the third communication unit 252 so that various processes of the A-DNS 25 are executed in an appropriate procedure based on the program stored in the third storage unit 251. The third processing unit 253 executes processing based on the program stored in the third storage unit 251.

The third processing unit 253 includes a resolution request receiving unit 254 and an identification information transmitting unit 255. Each of these parts is a functional block realized by a program executed by the third processing unit 253. Each of these parts may be realized by a program executed on the VM realized by the program executed by the third processing unit 253. Further, each of these parts may be mounted on the A-DNS25 as firmware. The resolution request receiving unit 254 is an example of a transmission request receiving unit.

FIG. 7 is a diagram showing an example of the data structure of the identification information table T1 stored in the first storage unit 281. The identification information table T1 stores the PLMN number, the TAC (Tracking Area Code), and the PGW-U identification information in association with each other.

The PLMN number is identification information for uniquely identifying a network such as HPLMN20 or VPLMN10. TAC is identification information for identifying an area that subdivides the network. The PGW-U identification information is identification information for identifying the PGW-U that the PGW-C28 can communicate with, such as the name of the PGW-U. The PGW-U identification information may be TEID (Tunnel Endpoint ID). The PLMN number and TAC are examples of network identification information and area information, respectively.

The various data in the identification information table T1 are all preset by the home operator. For example, a combination of PLMN number and TAC is associated with PGW-U identification information indicating PGW-U arranged in the vicinity of the area specified by the combination.

In the identification information table T1, the TAC may not be stored, and only the PLMN number and the PGW-U identification information may be associated with each other. For example, when the number of PGW-U41 is smaller than the number of networks to which the HPLMN 20 interconnects, one PGW-U41 may be assigned to a plurality of VPLMN 10. In such a case, the TAC does not have to be stored because it is not necessary to assign a different PGW-U41 to each TAC that subdivides the VPLMN10.

FIG. 8 is a diagram showing an example of the data structure of the DNS table T2 stored in the third storage unit 251. The DNS table T2 stores the host name, the source, and the IP address in association with each other. The DNS table T2 is referenced when A-DNS25 receives a resolution request and transmits an IP address.

The host name is information for identifying the device. The source is the IP address or network address of the source device that sent the host name resolution request. The IP address is the IP address of the device corresponding to the host name.

In FIG. 8, a plurality of sources are associated with the host name "PGW-C-01", and different IP addresses are associated with each source. That is, when the A-DNS25 receives the resolution request of the host name of "PGW-C-01", it transmits a different IP address according to the IP address of the device that is the source of the resolution request. The host name does not have to be associated with the source. In FIG. 8, the source is not associated with the host name “Host-01”. That is, when the A-DNS25 receives the resolution request of "Host-01", it transmits a single IP address regardless of the source of the resolution request.

FIG. 9 is a sequence diagram showing a processing flow by the roaming communication system 1 until the first UE 50 performs roaming communication. This processing is realized by the processing unit of each device collaborating with its components based on the program stored in each device of the roaming communication system 1 in advance.

The first UE 50 transmits a connection request to the V-MME 13 (S101). The first UE 50 receives the broadcast signal transmitted from the V-eNB 11 and acquires the PLMN number of the VPLMN 10 included in the broadcast signal. When the acquired PLMN number is included in the OPLMN (Operator controlled PLMN) stored in advance in the first UE 50, the first UE 50 determines that roaming communication is possible, and establishes wireless communication with the V-eNB 11. The OPLMN is stored in, for example, a SIM (Subscriber Identity Module) stored in the first UE 50. The V-MME 13 receives the connection request transmitted from the first UE 50 that has established wireless communication via the V-eNB 11 and the V-SGW 12. The connection request includes the identification information (for example, IMSI) of the first UE 50.

Subsequently, the V-MME 13 acquires the subscriber information (S102). The V-MME 13 specifies the HSS 26 as the request destination of the subscriber information based on the identification information of the first UE 50 included in the received connection request. Subsequently, the V-MME 13 requests the specified HSS 26 to authenticate the identification information of the first UE 50. If the authentication is successful, the V-MME 13 acquires the subscriber information from the HSS 26. The subscriber information includes the IP address of the first UE 50, the APN to which the first UE 50 can be connected, request information regarding priority control and billing conditions, and the like. When the APN notified by the first UE 50 matches the APN included in the subscriber information acquired from the HSS 26, the V-MME 13 determines that the first UE 50 can roam. The APN is notified from the first UE 50 to the V-MME 13, for example, in response to the V-MME 13 that has acquired the subscriber information transmitting the APN notification request to the first UE 50.

Subsequently, the V-MME 13 acquires the identification information (IP address) of the PGW-C (S103). The V-MME 13 transmits the APN resolution request notified by the first UE 50 to the V-DNS14. Upon receiving the resolution request, the V-DNS14 transmits the identification information corresponding to the APN included in the resolution request acquired from the A-DNS25 to the V-MME 13. As a result, the V-MME 13 acquires the identification information of the PGW-C28. The V-DNS14 may acquire the identification information corresponding to the APN in advance from the A-DNS25 and store (cache) it, or may acquire it from the A-DNS25 in response to receiving the resolution request.

Subsequently, the V-MME 13 transmits a session setting request for the first UE 50 to the V-SGW 11 (S104). The session setting request includes session identification information, first UE50 identification information, first UE50 position information, PGW-C28 identification information, priority control, and request information regarding billing conditions. The position information of the first UE 50 includes the PLMN number of the VPLMN 10 and the TAC of the area where the first UE 50 is located. The session setting request is, for example, CreateSessionRequest for the default bearer. The V-SGW 11 receives the transmitted session setting request.

Subsequently, the V-SGW 11 that has received the session setting request transmits the session generation request to the PGW-C28 (S105). The V-SGW 11 transmits a session generation request to the PGW-C28 indicated in the identification information of the PGW-C28 included in the received session setting request. The session generation request includes identification information of the first UE 50, position information of the first UE 50, identification information of PGW-C28, request information regarding priority control and billing conditions, and the like. The session creation request is, for example, CreateSessionRequest for the default bearer. The generation request receiving unit 284 of the PGW-C28 receives the transmitted session generation request.

Subsequently, the acquisition unit 285 of the PGW-C28 acquires the policy information about the first UE 50 from the PCRF 29 (S106). The acquisition unit 285 extracts the identification information of the first UE 50 and the request information regarding the priority control and the billing condition from the received session generation request, and transmits the policy information transmission request including the extracted information to the PCRF 29. Upon receiving the policy information transmission request, the PCRF 29 transmits the policy information about the first UE 50 based on each information included in the policy information transmission request. The acquisition unit 285 of the PGW-C28 acquires by receiving the transmitted policy information. The policy information is, for example, a PCC (Policy and Charging Control) rule, and the transmission and reception of the policy information is performed, for example, as a part of the IP-CAN (IP-Connectivity Access Network) session establishment procedure.

Subsequently, the establishment request transmission unit 286 of the PGW-C28 determines the PGW-U for transmitting the session establishment request (S107). The establishment request transmission unit 286 acquires the PLMN number and TAC included in the received session generation request. Subsequently, the establishment request transmission unit 286 identifies the acquired PLMN number and the PGW-U identification information associated with the TAC with reference to the identification information table T1. Subsequently, the establishment request transmission unit 286 identifies the PGW-U41 corresponding to the specified PGW-U identification information as the PGW-U41 for transmitting the communication session establishment request.

Subsequently, the establishment request transmission unit 286 transmits the session establishment request to the PGW-U41 (S108). The establishment request transmission unit 286 determines the identification information of the PGW-C28 about the default bearer. Subsequently, the establishment request transmission unit 286 transmits a session establishment request including session information based on the acquired policy information and PGW-C28 identification information about the determined default bearer. The session establishment request is, for example, SxSessionEstablishmentRequest. The session information based on the policy information is, for example, PDR (Packet Detection Rule), FAR (Forwarding Action Rule), URR (Usage Reporting Rule), QoS (QoS Enforcement Rule), or the like. Further, the identification information about the default bearer is, for example, F-TEIDu (Fully Qualified TEID of a GTP-u tunnel). The PGW-U41 receives the transmitted session establishment request.

Subsequently, the establishment response transmission unit 414 of the PGW-U41 transmits the session establishment response to the PGW-C28. The establishment response transmission unit 414 stores the session information included in the received session establishment request and the identification information of the PGW-C28 about the default bearer. Subsequently, the establishment response transmission unit 414 transmits the session establishment response. The session establishment response is, for example, SxSessionEstablishmentResponse. The PGW-C28 receives the transmitted session establishment response. After that, the connection response is transmitted to the first UE 50, so that a communication session is established between the first UE 50 and the PGW-U41, and communication between the first UE 50 and the PDN 30 becomes possible.

Subsequently, the relay processing unit 415 relays the communication between the first UE 50 and the PDN 30 based on the received session establishment request (S109). For example, the relay processing unit 415 detects a data packet related to communication between the first UE 50 and the PDN 30 based on the PDR included in the session establishment request. Subsequently, the relay processing unit 415 performs priority control on the detected data packet based on the FAR and QER included in the session establishment request, and transfers the detected data packet. Further, the relay processing unit 415 transmits a report on the communication status between the first UE 50 and the PDN 30 based on the URR included in the session establishment request.

As an example of the relay process, a case where the policy information about the first UE 50 is "provide high-speed communication when the cumulative communication volume is equal to or less than a predetermined value and provide low-speed communication when the cumulative communication amount exceeds the predetermined value" will be described. .. In this case, the PCRF 29 transmits the policy information corresponding to the high-speed communication to the PGW-C28 in response to the policy information transmission request for the first UE 50 received from the PGW-C28. The establishment request transmission unit 286 of the PGW-C28 transmits a session establishment request including session information corresponding to high-speed communication to the PGW-U41 based on the acquired policy information. The relay processing unit 415 of the PGW-U41 detects a data packet related to communication between the first UE 50 and the PDN 30 based on the PDR included in the received session establishment request, and supports high-speed communication based on the FAR and QER. Transfer the data packet detected by the relay method. In addition, the relay processing unit 415 stores the communication amount of the transferred data packet.

The relay processing unit 415 transmits a report when the cumulative communication amount for the first UE 50 including the stored communication amount exceeds a predetermined value based on the URR included in the session establishment request. The report is received, for example, by OCS (Online Charging System; not shown). In this case, the OCS receiving the report requests the PCRF29 to resend the policy information corresponding to the low-speed communication. Subsequently, the PCRF 29 transmits the policy information corresponding to the low-speed communication to the PGW-C28. The PGW-C28 that has acquired the policy information transmits a session change request including the session information corresponding to the low-speed communication based on the policy information to the PGW-U41. After receiving the session change request, the PGW-U41 transfers a data packet related to communication between the first UE 50 and the PDN 30 by a relay method corresponding to low-speed communication. The session change request is, for example, SxSessionModificationRequest.

FIG. 10 is a flow chart showing an example of the flow of the identification information transmission process. The identification information transmission process is executed by the A-DNS 25 when the A-DNS 25 receives a resolution request including the APN in S103 or the like of FIG.

First, the resolution request receiving unit 254 of the A-DNS25 receives the resolution request including the APN (S201). The same APN is associated with PGW27 and PGW-C28.

Subsequently, the identification information transmission unit 255 determines whether or not the resolution request is transmitted from the VPLMN 10 (S202). For example, the identification information transmission unit 255 refers to the DNS table T2 and determines whether or not the IP address of the source of the resolution request is that of VPLMN10.

When it is determined that the resolution request is transmitted from the VPLMN10 (S202-Yes), the identification information transmission unit 255 transmits the identification information of the PGW-C28 to the source of the resolution request based on the DNS table T2. It is transmitted (S203) and the process is terminated. When it is determined that the resolution request is not transmitted from the VPLMN 10, that is, it is determined that the resolution request was transmitted from the HPLMN 20 (S202-No), the identification information transmission unit 255 transmits the identification information of the PGW 27 to the transmission source of the resolution request. (S204), and the process is terminated.

As described above, in the roaming communication system according to the embodiment, the plurality of PGW-U41s are arranged in the IPX. Further, the PGW-C28 determines the PGW-U41 that relays the communication between the first UE 50 and the PDN3 from among the plurality of PGW-U41s based on the PLMN number included in the communication session generation request. By doing so, the PGW-C28 can select the PGW-U41 arranged in the IPX40, which is geographically or network topologically close to the VPLMN10, and can reduce the communication delay. Further, the PGW-C28 reduces the processing load of the device that processes the data packet related to the communication between the first UE 50 and the PDN 30, and the possibility that these devices cause communication congestion.

Further, in the roaming communication system 1 according to the embodiment, the PGW-C28 is arranged in the HPLMN20 and is communicably connected to the PCRF29. By doing so, even if the PGW-U41 is arranged in the IPX40, the PGW-C28 can relay the communication between the first UE50 and the PDN30 based on the policy information acquired from the PCRF29. .. Then, the user can be applied with the policy information provided by the home operator even in roaming communication.

Further, in the roaming communication system 1 according to the embodiment, the A-DNS25 transmits the identification information of the PGW-C28 or the PGW27 depending on whether the resolution request including the host name of the PGW-C is received from the VPLMN10 or the HPLMN20. Send. By doing so, the first UE 50, which is a roaming terminal, can use the PGW-C28, and the second UE 60, which is a non-roaming terminal, can use the PGW 27. That is, even when the home operator has already provided the service using the PGW 27, the PGW 27 can be effectively used for the non-roaming terminal, and the roaming communication system 1 according to the present invention can be easily introduced.

Further, in the roaming communication system 1 according to the embodiment, the PGW-C28 is installed in the country of the second country, and the PGW-U41 is installed in the country of the first country. By doing so, the first UE 50 and the PGW-U41 are closer to each other geographically or in terms of network topology, and the communication delay of roaming communication is further reduced.

Further, in the roaming communication system 1 according to the embodiment, the PGW-C28 is installed in the country of the second country, and the PGW-U41 is installed in the country of the first country and a country different from the second country (third country). Will be installed. By doing so, even when the HPLMN 20 interconnects with a plurality of VPLMN 10, it becomes easy to reduce the communication delay of roaming communication for the first UE 50 located in each VPLMN 10. That is, by doing so, the PGW-U41 can be installed in a third country close to any of the plurality of countries in which the plurality of VPLMN10s are operated. Then, the PGW-U41 installed in the third country relays the roaming communication about the first UE 50 located in the plurality of VPLMN10s, so that the communication delay of these roaming communication is reduced.

The above description is for the case where both VPLMN10 and HPLMN20 are 4G, but the core network of HPLMN20 may be a 5G core network (5GC; 5G Core).

FIG. 11 is a schematic diagram for explaining an outline of the roaming communication system 2 in which the core network of the HPLMN 20 is 5GC. Hereinafter, the differences from the roaming communication system 1 of FIG. 3 will be described with reference to FIG. Note that FIG. 11 shows only the configuration related to the communication of the first UE 50.

The roaming communication system 2 has a VPLMN 10, an HPLMN 20, a DN (Data Network) 31, an IPX40, a first UE 50, and a second UE 60. The DN 31 corresponds to the PDN 30 in the roaming communication system 1.

HPLMN20 has A-DNS25, SMF210, UDM (Unified Data Management) 211 and PCF (Policy Control Function) 212. The SMF 210 is a device having a communication session management function. The SMF210 has an integrated PGW-C function, which enables communication with the V-SGW12. The UDM211 is a server that registers the location and manages subscriber information, authentication information, and the like. The function of HSS26 is integrated in UDM211 so that communication with V-MME13 becomes possible. The PCF212 is a server that manages policy information regarding priority control, billing conditions, and the like. The functions of PCRF29 are integrated in PCF212, which enables communication with PGW-C.

IPX40 has a plurality of UPFs (User Plane Function) 42. The UPF relays the user plane communication between the first UE 50 and the DN 31. The function of PGW-U is integrated in UPF42, which enables communication with V-SGW12 and the like.

With such a configuration, even if a home operator who has been operating 4G introduces 5GC, the communication delay of roaming communication can be similarly reduced.

In the roaming communication system 2, the core network of VPLMN10 may be 5GC. In this case, V-SMF and AMF (Access and Mobility Management Function) are provided instead of V-SGW 12 and V-MME 13, respectively. In this case, the SMF210 of HPLMN20 does not have to integrate the functions of PGW-C. Further, the UDM211 does not have to be integrated with the HSS function. Further, the function of PGW-U may not be integrated in UPF42.

It should be understood that one of ordinary skill in the art can make various changes, substitutions and modifications to this without departing from the spirit and scope of the invention. For example, the above-mentioned processing of each part may be executed in an appropriately different order within the scope of the present invention. In addition, the above-described embodiments and modifications may be carried out in appropriate combinations within the scope of the present invention.

1 Roaming communication system 25 A-DNS
254 Resolution request receiver 255 Identification information transmitter 28 PGW-C
284 Generation request receiving unit 285 Acquisition unit 286 Establishment request transmitting unit 29 PCRF
41 PGW-U
415 Relay processing unit

Claims (16)

1. A communication control device that manages a roaming communication session for the communication terminal and a plurality of relays for roaming communication included in the home network of the communication terminal, which is communicably connected to the visited network accessed by the communication terminal. A communication system equipped with a relay device
   The communication control device is
   A storage unit that stores network identification information in association with any of the plurality of relay devices.
   A generation request receiving unit that receives a session generation request for the communication terminal, including network identification information of the visited network.
   An establishment request transmission unit for transmitting a session establishment request for the communication terminal to any of the plurality of relay devices is provided.
   Each of the plurality of relay devices
   When the session establishment request is received, a relay processing unit that relays communication between the communication terminal and the packet data network based on the received session establishment request is provided.
   The establishment request transmission unit identifies the relay device associated with the network identification information included in the session generation request as the relay device that transmits the session establishment request.
   A communication system characterized by that.
2. Further equipped with a policy information management device that stores a plurality of policy information regarding priority control or billing conditions for a plurality of communication terminals.
   The communication control device further includes an acquisition unit that acquires policy information associated with the communication terminal from the policy information management device based on the session generation request.
   The establishment request transmission unit transmits a session establishment request including the acquired policy information, and then transmits the session establishment request.
   The relay processing unit relays the communication based on the policy information included in the session establishment request.
   The communication system according to claim 1.
3. Further provided with an identification information transmitting device included in the home network and a second communication control device for managing non-roaming communication sessions.
   The identification information transmitting device is
   A transmission request receiving unit that receives an identification information transmission request,
   When the received identification information transmission request is an identification information transmission request transmitted from the visited network, the identification information of the communication control device is transmitted to the visited network, and the received identification information transmission request is the home. -In the case of an identification information transmission request transmitted from the network, the identification information transmission unit that transmits the identification information of the second communication control device to the home network is provided.
   The communication system according to claim 1 or 2.
4. The network identification information is a PLMN (Public Land Mobile Network) number.
   The communication system according to any one of claims 1-3.
5. The storage unit further associates and stores the area information for identifying the area in the network shown in the network identification information with any of the plurality of relay devices, and stores the area information.
   The establishment request transmission unit relays the session establishment request to the relay device associated with the area information of the area where the communication terminal is located in the visited network shown in the network identification information included in the session generation request. Identify as a device,
   The communication system according to any one of claims 1-4.
6. The area information is TAC (Tracking Area Code).
   The communication system according to claim 5.
7. The communication control device is PGW (Packet Data Network Gateway) -C (Control Plane), and the relay device is PGW-U (User Plane).
   The communication system according to any one of claims 1-6.
8. The communication control device is installed in a second country in which the home network is operated, which is different from the first country in which the visited network is operated.
   The relay device is installed in the country of the first country.
   The communication system according to any one of claims 1-7.
9. The communication control device is installed in a second country in which the home network is operated, which is different from the first country in which the visited network is operated.
   The relay device is installed in a country different from the first country and the second country.
   The communication system according to any one of claims 1-7.
10. A communication control device that manages a roaming communication session for the communication terminal and a plurality of relays for roaming communication included in the home network of the communication terminal, which is communicably connected to the visited network accessed by the communication terminal. It is a communication method using a communication system equipped with a relay device.
    The communication control device
    The network identification information is stored in association with any one of the plurality of relay devices.
    Receives a session generation request for the communication terminal, including network identification information for the visited network,
    A session establishment request for the communication terminal is transmitted to any one of the plurality of relay devices.
    Each of the plurality of relay devices
    When the session establishment request is received, the communication between the communication terminal and the packet data network is relayed based on the received communication session establishment request.
    Including that
    In the transmission of the session establishment request, the relay device associated with the network identification information included in the session generation request is specified as the relay device for transmitting the session establishment request.
    A communication method characterized by that.
11. A communication control device that manages a roaming communication session for the communication terminal and a plurality of relays for roaming communication included in the home network of the communication terminal, which is communicably connected to the visited network accessed by the communication terminal. A communication control device for a communication system equipped with a relay device.
    A storage unit that stores network identification information in association with any of the plurality of relay devices.
    A generation request receiving unit that receives a session generation request for the communication terminal, including network identification information of the visited network.
    A session establishment request is made to any of the plurality of relay devices for the relay device to relay communication between the communication terminal and the packet data network for the communication terminal. The establishment request transmitter to send and
    With
    The establishment request transmission unit identifies the relay device associated with the network identification information of the visited network included in the session generation request as the relay device for transmitting the session establishment request.
    A communication control device characterized by the fact that.
12. A communication control device that manages a roaming communication session for the communication terminal and a plurality of relays for roaming communication included in the home network of the communication terminal, which is communicably connected to the visited network accessed by the communication terminal. It is a communication control method by a communication control device of a communication system equipped with a relay device.
    The network identification information is stored in association with any one of the plurality of relay devices.
    Receives a session generation request for the communication terminal, including network identification information for the visited network,
    A session establishment request is made to any of the plurality of relay devices for the relay device to relay communication between the communication terminal and the packet data network for the communication terminal. Send,
    Including that
    In transmitting the session establishment request, the relay device associated with the network identification information of the visited network included in the session generation request is specified as the relay device for transmitting the session establishment request.
    A communication control method characterized by that.
13. A communication control device that manages a roaming communication session for the communication terminal and a plurality of relays for roaming communication included in the home network of the communication terminal, which is communicably connected to the visited network accessed by the communication terminal. A program for a communication control device of a communication system equipped with a relay device.
    The network identification information is stored in association with any one of the plurality of relay devices.
    Receives a session generation request for the communication terminal, including network identification information for the visited network,
    A session establishment request is made to any of the plurality of relay devices for the relay device to relay communication between the communication terminal and the packet data network for the communication terminal. Send,
    Let the communication control device do this,
    In transmitting the session establishment request, the relay device associated with the network identification information of the visited network included in the session generation request is specified as the relay device for transmitting the session establishment request.
    A communication control method characterized by that.
14. A communication control device that manages a roaming communication session for the communication terminal and a plurality of relays for roaming communication included in the home network of the communication terminal, which is communicably connected to the visited network accessed by the communication terminal. A relay device for a communication system equipped with a relay device.
    When the communication control device receives the session establishment request transmitted to the relay device associated with the network identification information of the visited network included in the session generation request for the communication terminal, the received session establishment request is received. A relay device comprising a relay processing unit that relays communication between the communication terminal and a packet data network based on the above.
15. A communication control device that manages roaming communication sessions for the communication terminal and a plurality of relays for roaming communication included in the home network of the communication terminal, which is communicably connected to the visited network accessed by the communication terminal. It is a relay method using a relay device of a communication system equipped with a relay device.
    When the communication control device receives the session establishment request transmitted to the relay device associated with the network identification information of the visited network included in the session generation request for the communication terminal, the received session establishment request is received. A method of relaying, comprising relaying communication between the communication terminal and a packet data network based on the above.
16. A communication control device that manages a roaming communication session for the communication terminal and a plurality of relays for roaming communication included in the home network of the communication terminal, which is communicably connected to the visited network accessed by the communication terminal. A program for a relay device of a communication system equipped with a relay device.
    When the communication control device receives the session establishment request transmitted to the relay device associated with the network identification information of the visited network included in the session generation request for the communication terminal, the received session establishment request is received. A program comprising, on the basis of, causing the relay device to relay communication between the communication terminal and the packet data network.

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