Terminal device, processing device, and control method for reducing the load during the registration process of terminal devices to IMS.

Abstract

To reduce the processing load during registration of terminal devices for IMS communication in a cellular communication system. [Solution] A terminal device of a cellular communication system has an acquisition means that obtains certification information from a device that manages subscriber information related to the terminal device in the cellular communication system to prove that authentication has been performed in registering the terminal device's information to the cellular communication system, and transmits the aforementioned certification information, along with a Session Initiation Protocol (SIP) Register message for registration to the Internet Protocol (IP) Multimedia Subsystem (IMS), to the IMS.

Description

Technical Field

[0001] The present invention provides a technique for reducing the load in the registration process of a terminal device to IMS.

Background Art

[0002] In cellular communication, as a mechanism for constructing a communication service based on Internet Protocol (IP), IP Multimedia Subsystem (IMS) has been introduced. The IMS server exchanges information with the server of the cellular communication system where the user terminal (UE), which is the service user, is registered, performs the registration of the UE to the IMS based on the information, and provides services to the UE.

Summary of the Invention

Problems to be Solved by the Invention

[0003] As described above, the IMS server needs to perform communication for information exchange with the server of the cellular communication system for providing its services. On the other hand, the load due to this communication is not low, and the introduction of a mechanism for reducing this load is required.

Means for Solving the Problems

[0004] The present invention provides a technique for reducing the processing load at the time of registration of a terminal device for performing IMS communication in a cellular communication system.

[0005] A terminal device according to one aspect of the present invention is a terminal device for a cellular communication system, comprising: an acquisition means for acquiring certification information from a device that manages subscriber information relating to the terminal device in the cellular communication system, for proving that authentication has been performed in the registration of the terminal device's information to the cellular communication system; and a transmission means for including the certification information in a Session Initiation Protocol (SIP) Register message for registration to the Internet Protocol (IP) Multimedia Subsystem (IMS) and transmitting it to the IMS.

[0006] A processing device according to one aspect of the present invention is a processing device for managing subscriber information relating to a terminal device in a cellular communication system, and includes a means for providing certification information to the terminal device to prove to the Internet Protocol (IP) Multimedia Subsystem (IMS) that authentication was performed when the information of the terminal device was registered in the cellular communication system.

[0007] A processing device according to one aspect of the present invention is a processing device that implements the Serving-Call Session Control Function (S-CSCF) of the Internet Protocol (IP) Multimedia Subsystem (IMS), and comprises: receiving means for receiving a Session Initiation Protocol (SIP) Register message from a terminal device in a cellular communication system; and processing means for processing the registration of the terminal device to the IMS, wherein the processing means performs the registration processing, including sending a Multimedia-Authentication-Request (MAR) message and receiving a Multimedia-Authentication-Answer (MAA) message, to a device that manages subscriber information relating to the terminal device in the cellular communication system, when the SIP Register message does not contain certification information to prove that authentication has been performed in the registration of the terminal device's information to the cellular communication system, or when IPsec (Security Architecture for Internet Protocol) is used in the IMS, and when IPsec is not used in the IMS and the SIP Based on the fact that the Register message contains the aforementioned certification information, the sending of the MAR message and the receiving of the MAA message are omitted, and the registration process is performed while omitting the authentication process that is executed when using IPsec. [Effects of the Invention]

[0008] According to the present invention, the processing load during registration of terminal devices for IMS communication in a cellular communication system can be reduced. [Brief explanation of the drawing]

[0009] [Figure 1] This figure shows an example of a system configuration. [Figure 2]This figure shows an example of the process flow for registering a UE (User Application) with IMS (Information Management System) based on a conventional fourth-generation (4G) cellular communication system. [Figure 3] This diagram shows an example of the process flow for registering a UE (User Application) with IMS (Information Management System) based on a conventional fifth-generation (5G) cellular communication system. [Figure 4] This figure shows a first example of the process flow for registering a UE with IMS according to this embodiment. [Figure 5] This figure shows a second example of the process flow for registering a UE with IMS according to this embodiment. [Figure 6] This diagram illustrates how roaming is determined in Third Party Registration. [Figure 7] This figure shows an example of the process performed in IMS. [Figure 8] This diagram shows an example of the hardware configuration of each device that makes up the system. [Figure 9] This figure shows an example of the functional configuration of a terminal device. [Figure 10] This figure shows an example of the functional configuration of a device in which HSS or UDM / HSS is implemented. [Figure 11] This figure shows an example of the functional configuration of a device in which I-CSCF or S-CSCF is implemented. [Modes for carrying out the invention]

[0010] The embodiments will be described in detail below with reference to the attached drawings. Note that the following embodiments do not limit the invention as defined in the claims, and not all combinations of features described in the embodiments are essential to the invention. Two or more of the features described in the embodiments may be combined in any way. Furthermore, identical or similar configurations will be given the same reference numeral, and redundant descriptions will be omitted.

[0011] (System Configuration) Figures 1(A) and 1(B) show examples of the configuration of a wireless communication system according to this embodiment. Figure 1(A) shows the configuration of a system combining a fourth-generation (4G) cellular communication system and the Internet Protocol (IP) Multimedia Subsystem (IMS). Figure 1(B) shows the configuration of a system combining a fifth-generation (5G) cellular communication system and the IMS. Note that Figures 1(A) and 1(B) only show configurations related to this embodiment, and cellular communication systems such as 4G and 5G naturally have functional configurations other than those shown. In this embodiment, the technical configuration is described in the context of a 4G or 5G system, but this is just an example, and each of the processes described below may be executed in nodes and functions that have similar functions to 4G and 5G in 6G and later cellular communication systems. Each of the functions shown in Figures 1(A) and 1(B) may be implemented by separate processing units, or multiple functions may be implemented by a single processing unit. Alternatively, one function may be implemented by multiple processing units.

[0012] In this embodiment, a communication service using IMS (e.g., an IP-based voice communication service) is provided to the user terminal (UE). To this end, the UE needs to register with the cellular communication system to receive communication services and with the IMS to receive IMS communication services. Figure 2 shows an example of the flow of the UE's registration process with the cellular communication system and the IMS in the system shown in Figure 1(A).

[0013] The UE sends an Attach Request to the Mobility Management Entity (MME) via the base station (eNodeB) (S201) when, for example, it is powered on or moves from outside the service area into the service area. In response to this request, the MME communicates with the Home Subscriber Server (HSS), and a message indicating that the HSS has authorized the UE's registration is sent to the UE via the MME (S202). This completes the UE's registration (attachment) to the cellular communication system. After completing registration to the cellular communication system, the UE sends a message to the IMS via the eNodeB, Serving Gateway (SGW), and Packet data network Gateway (PGW) to register with the IMS. The UE sends a Session Initiation Protocol (SIP) Register message (S203).

[0014] The message is then relayed by the Proxy-Call Session Control Function (P-CSCF) and forwarded to the Interrogating-CSCF (I-CSCF) (S204). The I-CSCF sends a User-Authorization-Request (UAR) to the HSS for UE authentication (S205) and receives a User-Authorization-Answer (UAA) (S206). This allows the I-CSCF to confirm that the UE that sent the SIP Register is a legitimate UE registered with the HSS, and forwards the SIP Register message to the S-CSCF selected by the HSS as the Serving-CSCF (S-CSCF) to register the UE (S207). Upon receiving the SIP Register message, the S-CSCF sends a Multimedia-Authentication-Request (MAR) to the HSS to obtain information for the UE authentication process (S208). Upon receiving the MAR, the HSS issues the information necessary for authentication and sends it to the S-CSCF in the Multimedia-Authentication-Answer (MAA) (S209). For example, the HSS generates a random number RAND, and uses RAND and the long-term shared key KI to generate the network authentication token AUTN, the expected response value XRES from the UE, the confidential key Ck used in IPsec (Security Architecture for Internet Protocol), and the integrity check key Ik. The HSS then sends RAND, AUTN, XRES, Ck, and Ik to the S-CSCF in the MAA.

[0015] S-CSCF holds XRES and sends an Unauthorized Challenge containing RAND, AUTN, Ck, and Ik to I-CSCF (S210). I-CSCF then forwards the Unauthorized Challenge to P-CSCF (S211). P-CSCF holds Ck and Ik and sends an Unauthorized Challenge containing RAND and AUTN to UE (S212). UE performs network authentication by comparing the value calculated using the received RAND and long-term key Ki with the value derived from AUTN. UE also calculates Ck, Ik, and the response value RES. Finally, UE sends a SIP Register containing RES to IMS (S213). The SIP Register is forwarded to the I-CSCF via the P-CSCF (S214). Upon receiving this SIP Register, the I-CSCF sends and receives UAR and UAA with the HSS, similar to S205 and S206 (S215, S216), and then sends the SIP Register including the RES to the S-CSCF (S217). The S-CSCF determines that the UE authentication was successful by confirming that the received RES matches the XRES received in S209, and registers the UE with the IMS. Subsequently, the S-CSCF sends a Server-Assignment-Request (SAR) to the HSS (S218) to notify the HSS that the UE has been registered. The HSS then sends a Server-Assignment-Answer (SAA) to the S-CSCF (S219) to notify the S-CSCF of the UE's user profile. Then, S-CSCF notifies the UE via I-CSCF and P-CSCF that the series of processes has been completed (S220).

[0016] Note that, in the system of FIG. 1(B), the process flow of the UE's registration to the cellular communication system and IMS is the same as that of FIG. 2, except that the MME and HSS in FIG. 2 are replaced by the Access and Mobility Management Function (AMF) and Unified Data Management (UDM) / HSS, respectively (and the names of the corresponding messages, etc.). That is, in S301 to S320 of FIG. 3, the same processing as that of S201 to S220 of FIG. 2 is performed.

[0017] As shown in FIGS. 2 and 3, when the UE registers to the IMS, access to the HSS (or UDM / HSS) occurs frequently from the I-CSCF and S-CSCF. And such processing is performed every time the UE returns (for example, due to moving from out of the coverage area to within the coverage area or powering on) after leaving the network (for example, due to moving out of the coverage area or powering off). Therefore, there is a possibility that the HSS (or UDM / HSS) becomes overloaded for the UE's registration to the IMS, and the performance of the entire network deteriorates. In this embodiment, in view of such circumstances, a technique for suppressing an increase in the load in the HSS (or UDM / HSS) is provided.

[0018] (Processing Example 1) FIG. 4 shows an example of the process flow of the method for the UE to register to the IMS according to this embodiment. Although this processing example is described in the context of 4G, it is of course applicable to 5G as well, and can be applied in the same procedure in subsequent standards. Also, in this processing example, the same reference numerals are assigned to the same processing as that of FIG. 2, and the detailed description thereof is omitted.

[0019] In this example, when the HSS receives a request from a UE to register with the cellular communication system (S201), it queries a predetermined database, for example, to determine whether the UE has been previously registered in an S-CSCF (S401). The database may be located inside or outside the processing unit on which the HSS is implemented. The database may also set an expiration date for the information of the S-CSCF to which each UE is registered. When the database receives a query from the HSS regarding a specific UE, if it holds information about an S-CSCF for that UE that has not yet expired, it may return the information about that S-CSCF to the HSS. If the database does not hold information about an S-CSCF for that UE that has not yet expired, it may return information to the HSS indicating that there is no registered S-CSCF. The database may also periodically query one or more S-CSCFs to obtain information about UEs that are currently registered. The database then stores the UE information obtained from each S-CSCF, associating it with the information of that S-CSCF, and can provide the HSS with the S-CSCF information associated with a specific UE in response to a query from the HSS regarding that UE. The S-CSCF information may be, but is not limited to, the address and name of the S-CSCF; any information that allows access to that S-CSCF based on that information can be used as the S-CSCF information.

[0020] If the HSS is unable to obtain the S-CSCF information, it notifies the UE that registration with the cellular communication system is complete, following the same procedure as in Figure 2, and allows the UE to register with the IMS through conventional processing. On the other hand, if the HSS is able to obtain the S-CSCF information, it sends that S-CSCF information to the UE (S402). The HSS may also notify the UE of tamper-proof data to prevent alteration of the S-CSCF information. For example, the HSS may include this information in an Update Location Answer (ULA) message and send that ULA message to the MME. The ULA message is a response message to an Update Location Request (ULR) message sent from the MME for UE registration. In one example, a new information element (IE) may be added to the ULA message to enable the transmission of the S-CSCF information (and, if necessary, tamper-proof data) in which the UE is registered. Additionally, a new message from the HSS to the MME may be defined.

[0021] The MME may extract information about the S-CSCF in which the UE is registered (and, if necessary, data to prevent tampering) from the ULA message, include this information in a Non-Access Stratum (NAS) message, and send the NAS message to the UE. The NAS message may be an Attach Accept message, which is a response to an Attach Request message sent from the UE to the MME. For example, a new information element (IE) may be added to the Attach Accept message to enable the transmission of information about the S-CSCF in which the UE is registered (and, if necessary, data to prevent tampering). Alternatively, an EMM Information message may be used, which is an optional NAS message that can be sent from the MME to the UE at the end of the procedure for registering the UE with the cellular communication system (Attach procedure). EMM stands for EPS Mobility Management, and EPS stands for Evolved Packet System. For example, a new IE may be added to the EMM Information message to enable the transmission of information about the S-CSCF in which the UE is registered (and, if necessary, data to prevent tampering). A new message from the MME to the UE may also be defined.

[0022] Furthermore, information about the S-CSCF in which the UE is registered (and, if necessary, data to prevent tampering) may be transmitted by control information unrelated to the Attach procedure. For example, a UE may perform a Tracking Area Update procedure for location registration, such as by moving across a tracking area. In this procedure, the UE may send a Tracking Area Update (TAU) Request message, and the MME may send a TAU Accept message to the UE. The MME may include information about the S-CSCF in which the UE is registered (and, if necessary, data to prevent tampering) in this TAU Accept message. In this case, for example, a new IE may be added to the TAU Accept message. The MME sends a notification to the HSS regarding a UE, for example, when a UE that was managed by another MME moves significantly and the MME takes over managing that UE. In response to this notification, the HSS updates the UE's registration information and, as described above, may also notify the HSS of information about the S-CSCF in which the UE is registered (and, if necessary, data to prevent tampering). For example, consider a case where a UE travels between a first area managed by a specific MME where IMS communication services are not provided, and a second area managed by the same MME where IMS communication services are provided. When the UE enters the second area from the first area, as described above, the S-CSCF information (and, if necessary, data to prevent tampering) that was registered when the UE previously stayed in the second area may be notified to the UE via the MME from the HSS.

[0023] The UE sends a SIP Register message containing the S-CSCF information (and, if received, tamper-proof data) received from the HSS (via the MME) to the IMS (via the P-CSCF to the I-CSCF and S-CSCF) (S403). The UE may, for example, send the S-CSCF information (and, if received, tamper-proof data) to the IMS as part of the Security-Client information in the SIP Register message. Alternatively, the UE may send the S-CSCF information (and, if received, tamper-proof data) to the IMS as a Contact parameter in the Contact header of the SIP Register message. Furthermore, the UE may include the S-CSCF information (and, if received, tamper-proof data) in the Authorization header of the SIP Register message and send it to the IMS.

[0024] At least one of the P-CSCF and I-CSCF checks whether the received SIP Register message contains information about the S-CSCF in which the UE is registered. If the I-CSCF finds that information in the SIP Register message, it omits sending the UAR, and consequently, also omits receiving the UAA from the HSS (S404, S405, S414, S415). This reduces the load on the HSS by decreasing the access from the I-CSCF to the HSS.

[0025] Furthermore, if the SIP Register message contains tamper-proof data, at least one of the P-CSCF and I-CSCF will use that data to verify that the information in the S-CSCF to which the UE is registered is data issued by the HSS (i.e., tamper-proof). In one example, a conventional digital signature mechanism can be used to prevent tampering. For example, the HSS and P-CSCF / I-CSCF each hold a private key, and the value obtained by hashing the original data using that private key can be used as tamper-proof data. This value is sent to the IMS via the UE, and the P-CSCF / I-CSCF can decrypt the value using its private key and determine whether the decryption result matches the original data, thereby confirming that the data has not been tampered with. The tamper-proof data may also include information about the validity period based on absolute time. In this case, the P-CSCF / I-CSCF will treat the information in the S-CSCF to which the UE is registered as valid information if the validity period included in the received tamper-proof data has not expired by the current time and no tampering has occurred. On the other hand, if the validity period in the tamper-proof data has expired by the current time, the P-CSCF / I-CSCF determines that the information in the S-CSCF where the UE is registered in the SIP Register message is invalid, and can perform the conventional processing without omitting the sending and receiving of UAR / UAA, as shown in Figure 2.

[0026] For tamper-proof data, CMAC (Cipher-based MAC) or HMAC (Hash-based MAC) may be used as the message authentication code (MAC). For example, CMAC-AES (CMAC-Advanced Encryption Standard) or CMAC-DES (CMAC-Data Encryption Standard) may be used as CMAC. For example, HMAC-MD5 (HMAC Code-MD5) or HMAC-SHA256 (HMAC Secure Hash Algorithm 256-bit) may be used as HMAC. Furthermore, for data specifications that store S-CSCF information (address or FQDN (Fully Qualified Domain Name)) and MAC values, for example, JWT (JSON Web Token) (RFC7519) may be used. However, these are just examples, and other tamper-proof data or data specifications may be used.

[0027] As described above, in this process, the processing of S404, S405, S414, and S415 is omitted, thereby reducing the load on the HSS. The I-CSCF identifies the S-CSCF to which the UE is registered based on the received information and forwards a SIP Register message to that S-CSCF. When the S-CSCF receives a SIP Register message containing information about the S-CSCF to which the UE is registered (and tamper-proof data if received), it can recognize that authentication with the HSS has been completed. For this reason, in this process, the transmission of MAR and reception of MAA by the S-CSCF can be further omitted (S407, S408). Note that the SIP Register message forwarded to the S-CSCF may contain information indicating that the UE has been confirmed to be registered in that S-CSCF, in which case the information about the S-CSCF to which the UE is registered (and tamper-proof data if received) may be deleted. Furthermore, the SIP Register message forwarded to the S-CSCF may retain its conventional format, and the processing performed by the S-CSCF may remain the same as before. For example, when communication using IPsec is performed, it is necessary to receive an MAA containing information for authentication processing by sending a MAR; therefore, S208 and S209 in Figure 2, and S210 to S214 and S217 corresponding to authentication processing, are not omitted. For this reason, the SIP Register message sent to the S-CSCF may contain only conventional information. Note that, as explained in this processing example, if a SIP Register message containing information about the S-CSCF in which the UE is registered (and tamper-proof data if received) is sent to the S-CSCF, the S-CSCF may ignore that information and perform conventional processing.

[0028] On the other hand, if IPsec is not used, all of the processing in S208 to S214 and S217 in Figure 2 can be omitted (S407 to S413, S416). This reduces the amount of signaling in the system, and in addition to the load on the HSS, it reduces the load on the entire system.

[0029] The subsequent processing is the same as in conventional processing (S218~S220). As described above, this processing example can reduce the amount of signaling between I-CSCF and HSS, and in particular reduce the load on HSS. Furthermore, in environments where IPsec is not used, the amount of signaling between S-CSCF and HSS can be reduced, and the signaling for UE authentication can be further reduced, thereby reducing the load not only on HSS but on the entire system.

[0030] (Processing Example 2) Figure 5 shows an example of the processing flow for registering a UE with IMS according to this embodiment. Although this processing example is explained in the context of 4G, it is naturally applicable to 5G and can be applied to subsequent standards using similar procedures. In this processing example, the same reference numerals are used for the same processes as in Figure 2, and their detailed explanations are omitted. The messages between each function described below may be those described in Processing Example 1. For example, the ULA message between HSS and MME, and the Attach Accept message, EMM Information message, and TAU Accept message between MME and UE may be sent with the new information described below included.

[0031] In this example, when the HSS receives a request from the UE to register with the cellular communication system (S201), it sends a message to the UE containing certification information that proves (at least to the IMS) that the UE was authenticated during the registration process (S501). The UE then sends a SIP Register message containing this certification information to the IMS (S502). When the I-CSCF receives this SIP Register, it confirms whether the UE is registered with the cellular communication system by sending a UAR and receiving a UAA, and after receiving the selection information of the S-CSCF to which the UE is registered (S205, S206), it forwards the SIP Register message containing the certification information to the selected S-CSCF (S503). Note that if the SIP Register message contains certification information, the I-CSCF may omit sending a UAR and receiving a UAA. In this case, the selection of S-CSCF may be left to the IMS side, or for example, the HSS may only perform the selection of S-CSCF when sending and receiving UAR and UAA, or a node other than the HSS may perform the selection of S-CSCF.

[0032] If the SIP Register message does not contain certification information, S-CSCF may perform the conventional IMS processing as shown in Figure 2. On the other hand, if the SIP Register message contains certification information, S-CSCF does not send MAR and receive MAA (S504, S505), and consequently, subsequent processing (S506~S513) is also omitted. Note that if IPsec is used, processing S504~S513 is not omitted. In this case, I-CSCF may send UAR and receive UAA in S511 and S512, but this processing may be omitted depending on whether processing S205 and S206 has been performed. Furthermore, even if processing S205 and S206 is omitted, this processing may also be omitted. This reduces access from IMS to HSS and reduces the load on HSS. It also reduces the amount and load of signaling for the entire network.

[0033] In one example, S-CSCF can determine whether a UE is roaming out based on the information contained in the SIP Register message, and for roaming out UEs, it can execute the conventional IMS processing shown in Figure 2, regardless of whether or not authentication information is present. The SIP Register message contains a P-Access Network Information (PANI) header, and the PANI header contains the Mobile Country Code (MCC) and Mobile Network Code (MNC). S-CSCF can determine whether a UE is roaming out by checking this PANI header. This allows, for example, UEs located on overseas networks to always undergo the conventional IMS registration process, and only reliably authenticated UEs to be allowed to register with IMS. Alternatively, I-CSCF may perform this determination, in which case it can always execute S205 and S206 for roaming out UEs, and omit S205 and S206 for UEs that are not roaming out (i.e., staying on the home network) and are the source UE of a SIP Register message containing authentication information.

[0034] Furthermore, as proof information, for example, a token valid for a certain short period may be issued by the HSS and notified to the UE. This token can be of any format whose legitimacy can be verified using key information held in the IMS (P-CSCF / I-CSCF / S-CSCF). The UE may include this token in the SIP Register message and send it to the IMS. The P-CSCF / I-CSCF / S-CSCF may then verify the token included in the SIP Register message using the key information held by its device, and if its legitimacy can be confirmed, it may determine that the UE has registered with the cellular communication system.

[0035] Furthermore, in one example, if a UE is configured to send SIP Register messages only when it is registered with the cellular communication system and a connection has been established, the IMS may refrain from performing any processing, including querying the HSS, upon receiving the SIP Register message. For example, when S-CSCF receives a SIP Register message, it may assume that the sending UE is registered with the HSS and omit sending the MAR and receiving the MAA, as well as the subsequent series of processing. However, even in this case, if IPsec is used, these processing steps will not be omitted. Similarly, when I-CSCF receives a SIP Register message, it may assume that the sending UE is registered with the HSS and omit sending the UAR and receiving the UAA. S-CSCF and I-CSCF may also check the access type (access-type or access-class) in the PANI header of the SIP Register message to determine whether the UE is accessing the cellular communication system. In other words, if the PANI header in the SIP Register message indicates that the access type is an access by a 3GPP cellular communication system, it is assumed that the UE is registered with the cellular communication system, and therefore, S-CSCF and I-CSCF may omit some processing. Depending on the network configuration, the UE may be configured to send the SIP Register message before completing registration with the cellular communication system. For this reason, for example, if registration with the cellular communication system is required to send a SIP Register message for a UE that is not roaming out, the IMS may omit processing if it is certain that the UE is not roaming out and that it is registered with the cellular communication system. In other words, even if certification information cannot be included in the SIP Register message, the IMS may decide whether to omit the sending and receiving of MAR / MAA and subsequent processing (sending and receiving of SAR / SAA in some cases) based solely on the roaming determination.

[0036] Furthermore, the information in the PANI header of the SIP Register message is set by the UE, and therefore may not always be valid. For this reason, for example, the HSS may include information about the UE's local network in the SAA, which is the response to the SAR sent in S514. For example, this information may be included in the Cx-User-Data profile of the SAA. This allows the S-CSCF to compare the information in the PANI header with the information provided by the HSS, and if both determine that the UE that sent the SIP Register message is not roaming out, then registration with IMS can be performed using a shortened procedure. That is, for example, the S-CSCF may skip steps S504-S513 based on the information in the PANI header, and then send the SAR (S514) and receive the SAA (S515). Then, the S-CSCF confirms that the UE is not roaming out based on the information contained in the SAA received in S515. In other words, S-CSCF verifies that the information in the PANI header of the SIP Register message received in S503 is correct. If the information contained in the SAA contradicts the contents of the PANI header, S-CSCF may determine that the SIP Register message was not a request from a legitimate UE, and may perform error handling without registering that UE with IMS.

[0037] Furthermore, after the processing shown in Figure 5, in which some processing is omitted based on the contents of the PANI header, the Third Party Registration process may be executed, for example, as shown in Figure 6, so that the Telephony Application Server (TAS) can perform a roaming determination of the UE with the HSS. The S-CSCF sends a SIP REGISTER to the TAS, and upon receiving the SIP REGISTER, the TAS sends a User-Data-Request to the HSS to inquire. The HSS then responds to the receipt of the User-Data-Request by sending a User-Data-Answer back to the TAS. This User-Data-Answer includes the Evolved Cell Global Identifier (ECGI), and the ECGI includes the PLMN-ID, which is a combination of the MCC and MNC. Therefore, the TAS can determine whether or not the UE is within the home network (whether or not it is roaming out) based on the PLMN-ID. The TAS can then include this determination result in a SIP 200 (REGISTER) and send it to the S-CSCF. Furthermore, SIP 200 (REGISTER) may include ECGI and PLMN-ID information, and roaming determination may be performed by S-CSCF. If S-CSCF determines that a UE is roaming out, it may determine that the SIP Register message was not a legitimate request from the UE because it contradicts the contents of the PANI header, and may perform error handling without registering that UE with IMS.

[0038] Figure 7 shows an example of the processing flow performed by IMS in this example. Note that this is just one example; for example, some steps may be omitted, multiple steps may be combined into one step, or one step may be divided into multiple steps. In the following description, we will explain the case where S-CSCF performs the processing, but some parts of the processing may be performed by other functional parts of IMS, such as I-CSCF. Also, when using IPsec, IMS may perform the conventional IMS registration process without performing the processing shown in Figure 7.

[0039] First, upon receiving a SIP Register message, S-CSCF determines whether the message contains authentication information (e.g., a token) used during cellular communication registration (S701). If S-CSCF determines that the SIP Register message does not contain authentication information (NO in S701), it executes the conventional IMS registration process as shown in Figure 2 (S704) and terminates the process. On the other hand, if S-CSCF determines that the SIP Register message contains authentication information (YES in S701), it then checks the information in the PANI header of the SIP Register message to determine whether the UE is roaming out (S702). In other words, S-CSCF determines whether the UE is located within the home network. If S-CSCF determines that the UE is roaming out (located on a different network than the home network) (YES in S702), it executes the conventional IMS registration process as shown in Figure 2 (S704) and terminates the process.

[0040] If the UE is not roaming out (is in the home network) (NO in S702), S-CSCF omits processing S504-S513 as explained in relation to Figure 5 (S703). Then, S-CSCF sends a SAR and receives an SAA containing information about the network where the UE is located. S-CSCF then determines whether the UE is roaming out or not based on the information about the network where the UE is located (S705). If S-CSCF determines that the network where the UE is located is the home network (not roaming out), after processing S220, it performs Third Party Registration and determines whether the UE is roaming out or not through information exchange between TAS and HSS (S706). If S-CSCF determines through information exchange between TAS and HSS that the UE is not roaming out (is in the home network) (NO in S706), it successfully registers the UE with IMS and terminates processing. On the other hand, if S-CSCF determines in S705 and S706 that the UE is roaming out (is in a different network than the home network) (YES in S705 or S706), it will perform error handling (S707) because this contradicts the determination result in S702, and will terminate processing without registering the UE with IMS.

[0041] In this way, IMS can omit some of the conventional IMS registration process for UEs that are certain to be registered with the cellular communication system, assuming that authentication for their registration has been completed. This reduces the processing load related to UE registration with IMS, particularly the processing load on HSS.

[0042] As described above, each of the processes explained is applicable to cellular communication systems that succeed 4G, such as 5G. However, non-substantive changes, such as message names, will be made for this application. For example, the Attach Request / Attach Accept in 4G described above can be replaced with Registration Request (Initial Registration) / Registration Accept in 5G. Similarly, the Tracking Area Update Request / Tracking Area Update Accept in 4G can be replaced with Registration Request (Mobility Registration Update) / Registration Accept in 5G. Furthermore, the Update Location Request / Update Location Answer in 4G can be replaced with Nudm UECM Registration Request / Nudm UECM Registration Response in 5G. Note that Nudm UECM Registration may also be written as Nudm UEContextManagement. Thus, although message names may differ depending on the generation of the cellular communication system, the exchange of information described above can be carried out using corresponding messages with similar meanings. This reduces the processing load on nodes that have functions to manage subscriber information, such as HSS and UDM / HSS, as well as the load on the entire network.

[0043] (Device configuration) Next, an example of the configuration of the terminal device and each processing unit (for example, a processing unit on which the above-mentioned functions such as MME, HSS, P-CSCF, I-CSCF, and S-CSCF are implemented) according to this embodiment will be described with reference to Figure 8. In one example, each device is configured to include a processor 801, ROM 802, RAM 803, storage device 804, and communication circuit 805. The processor 801 is a computer configured to include one or more processing circuits, such as a general-purpose CPU (Central Processing Unit) or ASIC (Application-Specific Integrated Circuit), and executes the overall processing of the device and the above-mentioned processing by reading and executing programs stored in ROM 802 and storage device 804. ROM 802 is a read-only memory that stores information such as programs and various parameters related to the processing executed by each device. RAM 803 functions as a workspace when the processor 801 executes programs and is a random-access memory that stores temporary information. Storage device 804 is configured to include, for example, a removable external storage device. The communication circuit 805 is configured to include at least a circuit capable of performing the above-mentioned communication. Although Figure 8 shows one communication circuit 805, each device may have multiple communication circuits.

[0044] Figure 9 shows an example of the functional configuration of a terminal device that functions as an UE as described above. The terminal device includes, for example, an information acquisition unit 901 and an IMS registration request unit 902. These functional units can be realized, for example, by a processor 801 executing a program stored in a ROM 802 or a storage device 804. These functional units may also be implemented in a communication circuit 805. Furthermore, Figure 9 only illustrates the functional configuration of a terminal device related to this embodiment, and it naturally has the functions of a terminal device in a normal cellular communication system. Moreover, the terminal device only needs to have functions related to at least one of the embodiments described above, and some of the functions shown below may be omitted.

[0045] The information acquisition unit 901 acquires the above-mentioned information (S-CSCF information (and tamper-proof data) registered through past registration processes, and certification information to prove that it is registered in the cellular communication system) from the HSS or UDM / HSS that manage subscriber information of terminal devices in the cellular communication system, for example via the MME or AMF. The information acquisition unit 901 can acquire the above-mentioned information by sending request information, for example, a registration request to the cellular communication system or an update of the tracking area. The IMS registration request unit 902 sends the SIP Register message, including the information acquired by the information acquisition unit 901, to the IMS (P / I / S-CSCF).

[0046] Figure 10 shows an example of the functional configuration of a processing unit in which the above-described HSS or UDM / HSS functions are implemented. The processing unit includes, for example, a UE management unit 1001, a registration status determination unit 1002, and an information provision unit 1003. These functional units can be realized, for example, by a processor 801 executing a program stored in a ROM 802 or a storage device 804. These functional units may also be implemented in a communication circuit 805. Furthermore, Figure 10 only illustrates the functional configuration of an HSS or UDM / HSS related to this embodiment, and it naturally has the functions of an HSS or UDM / HSS in a normal cellular communication system. In addition, the processing unit only needs to have functions related to at least one of the embodiments described above, and some of the functions shown below may be omitted.

[0047] The UE management unit 1001 manages subscriber information for UEs in the cellular communication system. The registration status determination unit 1002 determines, for example, whether there is an S-CSCF that the UE has registered through past registration processes. If there is an S-CSCF that the UE has registered, the registration status determination unit 1002 obtains information such as the address of that S-CSCF by querying a database, for example. The information provision unit 1003 provides the information such as the address of the S-CSCF to the UE (via MME or AMF) once it has obtained this information. The information provision unit 1003 may also generate and provide tamper-proof data to the UE as needed to prevent tampering with the information of the S-CSCF.

[0048] Figure 11 shows an example of the functional configuration of a processing unit in which the above-described I-CSCF or S-CSCF functions are implemented. The processing unit includes, for example, an information extraction unit 1101, a processing execution determination unit 1102, and a registration processing unit 1103. These functional units can be realized, for example, by a processor 801 executing a program stored in a ROM 802 or a storage device 804. These functional units may also be implemented in a communication circuit 805. Furthermore, Figure 11 only illustrates the functional configuration of the I-CSCF related to this embodiment, and it naturally has the functions of a normal IMS I-CSCF. In addition, the processing unit only needs to have functions related to at least one of the embodiments described above, and some of the functions shown below may be omitted.

[0049] The I-CSCF and P-CSCF information extraction unit 1101 extracts information added by the UE from the SIP Register message received via the P-CSCF. For example, if the SIP Register message contains information such as the address of an S-CSCF registered by the UE through past registration processes, the information extraction unit 1101 extracts that information. The information extraction unit 1101 also extracts tamper-proof data to prevent alteration of the S-CSCF information if it is included in the SIP Register message. The information extraction unit 1101 extracts the S-CSCF information that has been confirmed not to have been altered by the tamper-proof data, and discards the S-CSCF information if it cannot be confirmed otherwise. Furthermore, if the SIP Register message contains certification information indicating that the UE has been authenticated in registering with the cellular communication system, the information extraction unit 1101 extracts that certification information. Furthermore, if the SIP Register message contains information about the expiration date of the information, and that expiration date has passed, the information extraction unit 1101 may discard that information even if it contains the aforementioned information. The information extraction unit 1101 may also extract information from the PANI header in the SIP Register message.

[0050] The processing execution determination unit 1102 determines, based on the information extracted by the information extraction unit 1101, whether to execute the conventional processing or to omit part of it.

[0051] For example, if the I-CSCF processing execution determination unit 1102 extracts information from an unaltered S-CSCF, it may omit the UAR transmission and UAA reception processes as shown in S404, S405, S414, and S415 in Figure 4, and otherwise execute the conventional process. Also, if the above-mentioned certification information is extracted and the processes S504 to S510 in Figure 5 are omitted, the I-CSCF processing execution determination unit 1102 may omit the UAR transmission and UAA reception processes in S511 and S512. However, if the above-mentioned certification information is extracted, the I-CSCF processing execution determination unit 1102 may execute the conventional process without omitting any processes. Furthermore, if the above-mentioned certification information is extracted and the S-CSCF to which the UE is registered can be identified by prior configuration or the like, the I-CSCF processing execution determination unit 1102 may omit the UAR transmission and UAA reception processes in S205 and S206 in Figure 5. Furthermore, the I-CSCF processing execution determination unit 1102 may determine, for example, that if it is determined that the UE has not roamed out based on the PANI header information in the SIP Register message, it may perform the same processing as when certification information is extracted.

[0052] Furthermore, if the S-CSCF processing execution determination unit 1102 extracts tamper-free S-CSCF information and does not use IPsec, it omits the SAR transmission and SAA reception processing, as shown in S407 and S408 of Figure 4, and also omits the subsequent processing from S409 onwards. Also, if the S-CSCF processing execution determination unit 1102 determines, for example, based on the PANI header information in the SIP Register message, that the UE is not roaming out and does not use IPsec, it omits the MAR transmission and MAA reception processing, as shown in S504 and S505 of Figure 5, and also omits the subsequent processing from S506 onwards. In addition, the S-CSCF processing execution determination unit 1102 may be configured to determine whether or not the UE is roaming out when the above-mentioned certification information is extracted.

[0053] The registration processing unit 1103 executes the process that the processing execution determination unit 1102 has determined to execute. Note that if the processing in S504 to S513 is omitted in Figure 5, and the registration processing unit 1103 determines in S515 that the UE is roaming out based on the information contained in the SAA received, it may discard the information related to the registration process up to that point and execute error processing. Furthermore, if the processing in S504 to S513 is omitted in Figure 5, and the registration processing unit 1103 determines that the UE is roaming out in the Third Party Registration after processing S220, it may discard the information related to the registration process up to that point and execute error processing.

[0054] As described above, the cellular communication system and IMS according to this embodiment are configured to omit some of the processing that was conventionally performed based on the content of the SIP Register message transmitted from the UE. Furthermore, the information included in the SIP Register message set by the UE is provided by a device that manages subscriber information about the UE, such as an HSS or UDM / HSS, and the IMS registers the UE using a procedure in which some processing is omitted if the legitimacy of the information is guaranteed. This makes it possible to reduce the load on the IMS related to the UE registration process while preventing the registration of UEs based on illegitimate requests. Thus, it becomes possible to contribute to Goal 9 of the United Nations Sustainable Development Goals (SDGs), "Build resilient infrastructure, promote sustainable industrialization and foster innovation."

[0055] The invention is not limited to the embodiments described above, and various modifications and changes are possible within the scope of the gist of the invention.

Claims

1. A terminal device for a cellular communication system, Acquisition means for acquiring certification information from a device that manages subscriber information relating to the terminal device in the cellular communication system, to prove that authentication was performed in the registration of the terminal device's information to the cellular communication system, A transmission means for sending a Session Initiation Protocol (SIP) Registerer message to the Internet Protocol (IP) Multimedia Subsystem (IMS), including the aforementioned certification information, to the IMS. A terminal device characterized by having the following features.

2. The terminal device according to claim 1, characterized in that the aforementioned certification information is a token issued by a device that manages subscriber information and is valid for a certain period of time, and the token is a token whose legitimacy can be verified by key information held in the IMS.

3. The terminal device according to claim 1, characterized in that the acquisition means transmits a message to a device that manages subscriber information requesting registration of the terminal device to the cellular communication system, and acquires the certification information in a message in response to the request.

4. The terminal device according to claim 1, wherein the device for managing subscriber information is a Home Subscriber Server (HSS) in a fourth-generation cellular communication system, or a Unified Data Management (UDM) / HSS in a fifth-generation cellular communication system, and the acquisition means acquires the certification information from the HSS via a fourth-generation Mobility Management Entity (MME), or from the UDM / HSS via a fifth-generation Access and Mobility Management Function (AMF).

5. A processing device for managing subscriber information relating to terminal devices in a cellular communication system, A processing device characterized by having a means for providing authentication information to the terminal device to prove to the Internet Protocol (IP) Multimedia Subsystem (IMS) that authentication was performed when the information of the terminal device was registered in the cellular communication system.

6. The processing apparatus according to claim 5, characterized in that the providing means issues a token which is valid for a certain period of time as the proof information and whose legitimacy can be verified by key information held in the IMS, and provides the token to the terminal device.

7. The processing apparatus according to claim 5, characterized in that when the providing means receives a message requesting registration of the terminal device to the cellular communication system, it provides the certification information to the terminal device in a message in response to the request.

8. The processing device is a Home Subscriber Server (HSS) in a fourth-generation cellular communication system, or a Unified Data Management (UDM) / HSS in a fifth-generation cellular communication system. The processing apparatus according to claim 5, characterized in that the providing means provides the certification information to the terminal device via a fourth-generation Mobility Management Entity (MME) when the processing apparatus is the HSS, or via a fifth-generation Access and Mobility Management Function (AMF) when the processing apparatus is the UDM / HSS.

9. A processing unit on which the Serving-Call Session Control Function (S-CSCF) of the Internet Protocol (IP) Multimedia Subsystem (IMS) is implemented, A receiving means for receiving Session Initiation Protocol (SIP) Register messages from terminal devices in a cellular communication system, Processing means for registering the terminal device to the IMS, It has, The processing means is If the SIP Register message does not contain certification information to prove that authentication was performed in the registration of the terminal device information to the cellular communication system, or if IPsec (Security Architecture for Internet Protocol) is used in the IMS, the registration process, including sending a Multimedia-Authentication-Request (MAR) message and receiving a Multimedia-Authentication-Answer (MAA) message, is performed on the device that manages subscriber information relating to the terminal device in the cellular communication system. Based on the fact that IPsec is not used in the IMS and the certification information is included in the SIP Register message, the sending of the MAR message and the receiving of the MAA message are omitted, and the registration process is performed while omitting the authentication process that would be performed when IPsec is used. A processing apparatus characterized by the following:

10. The aforementioned certification information is a token issued by the device that manages the subscriber information, and is valid for a limited period of time. The processing device further includes a holding means for holding key information for verifying the token, The processing device according to claim 9, characterized in that, if IPsec is not used in the IMS and the token contained in the SIP Register message is verified using the key information to confirm its legitimacy, the processing device omits the transmission of the MAR message and the reception of the MAA message, and performs the registration process that omits the authentication process performed when IPsec is used.

11. The system further includes a determination means that checks the P-Access Network Information (PANI) header contained in the SIP Register and determines whether the terminal device is roaming out based on the Mobile Country Code (MCC) and Mobile Network Code (MNC) contained in the PANI header, The processing device according to claim 9, characterized in that, when the terminal device is roaming out, the processing means performs the registration process, including sending the MAR message and receiving the MAA message, even if the certification information is included in the SIP Register message.

12. The processing means is In the registration process, which omits the transmission of the MAR message and the reception of the MAA message, and omits the authentication process performed when using IPsec, the following actions are performed with respect to the device that manages the subscriber information: transmission of a Server-Assistant-Request (SAR) message and reception of a Server-Assistant-Answer (SAA) message; If the SAA message contains information indicating that the terminal device is roaming out, error processing will be performed without registering the terminal device with the IMS. The apparatus according to feature 9.

13. The processing means is After the registration process, which omits the transmission of the MAR message and the reception of the MAA message, and omits the authentication process performed when using IPsec, information is obtained as a result of the roaming determination of the terminal device performed between the Telephone Application Server (TAS) and the device that manages the subscriber information. If information is obtained indicating that the terminal device is roaming out, error processing is performed without registering the terminal device with the IMS. The apparatus according to feature 9.

14. A control method performed by a terminal device of a cellular communication system, From a device that manages subscriber information relating to the terminal device in the cellular communication system, obtain certification information to prove that authentication was performed in the registration of the terminal device's information to the cellular communication system. Sending a Session Initiation Protocol (SIP) Register message containing the aforementioned certification information to the Internet Protocol (IP) Multimedia Subsystem (IMS) for registration with the IMS, A control method characterized by including

15. A control method performed by a processing device that manages subscriber information relating to a terminal device in a cellular communication system, A control method characterized by providing the terminal device with authentication information to prove to the Internet Protocol (IP) Multimedia Subsystem (IMS) that authentication was performed when the information of the terminal device was registered in the cellular communication system.

16. A control method executed by a processing unit that implements the Serving-Call Session Control Function (S-CSCF) of the Internet Protocol (IP) Multimedia Subsystem (IMS), A receiving process in which a Session Initiation Protocol (SIP) Register message is received from a terminal device in a cellular communication system, A processing step for registering the terminal device with the IMS, It has, In the aforementioned processing step, If the SIP Register message does not contain certification information to prove that authentication was performed in the registration of the terminal device information to the cellular communication system, or if IPsec (Security Architecture for Internet Protocol) is used in the IMS, the registration process, including sending a Multimedia-Authentication-Request (MAR) message and receiving a Multimedia-Authentication-Answer (MAA) message, is performed on the device that manages subscriber information relating to the terminal device in the cellular communication system. Based on the fact that IPsec is not used in the IMS and the certification information is included in the SIP Register message, the sending of the MAR message and the receiving of the MAA message are omitted, and the registration process is performed while omitting the authentication process that would be performed when IPsec is used. A control method characterized by the following:

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