Terminal device, processing device, and control method for reducing load in registration processing of terminal device to IMS

Abstract

According to the present invention, a terminal device of a cellular communication system acquires, from a device that manages subscriber information related to the terminal device in the cellular communication system, information on a Serving-Call Session Control Function (S-CSCF) of the Internet Protocol (IP) Multimedia Subsystem (IMS) in which the terminal device is registered through a past registration process, includes the information thereof in a Session Initiation Protocol (SIP) Register message for registration to the IMS, and transmits the message to the IMS.

Description

Terminal device, processing device, and control method for reducing load in registration process of terminal device to IMS

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

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

[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.

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

[0005] A terminal device according to an aspect of the present invention is a terminal device of a cellular communication system, and includes an acquisition unit that acquires information on a Serving-Call Session Control Function (S-CSCF) of an Internet Protocol (IP) Multimedia Subsystem (IMS) to which the terminal device is registered by a past registration process from a device that manages subscriber information regarding the terminal device in the cellular communication system, and a transmission unit that transmits a Session Initiation Protocol (SIP) Register message for registration to the IMS including the information 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: determination means for determining whether there is a Serving-Call Session Control Function (S-CSCF) of Internet Protocol (IP) Multimedia Subsystem (IMS) in which the terminal device is registered through past registration processing; and providing means for providing information of the S-CSCF to the terminal device if such an S-CSCF exists.

[0007] A processing device according to one aspect of the present invention is a processing device on which the Interrogating-Call Session Control Function (I-CSCF) of the Internet Protocol (IP) Multimedia Subsystem (IMS) is implemented, and comprises: receiving means for receiving a Session Initiation Protocol (SIP) Register message from a terminal device of a cellular communication system; and processing means for processing registration of the terminal device to the IMS, wherein the processing means performs the SIP If the Register message does not contain information about an S-CSCF to which the terminal device is registered through past registration processing, a User-Authorization-Request (UAR) message is sent and a User-Authorization-Answer (UAA) message is received to the device that manages subscriber information related to the terminal device in the cellular communication system, and the SIP Register message is forwarded to the S-CSCF identified by the UAA. If the SIP Register message contains information about the S-CSCF, the sending of the UAR message and the receiving of the UAA message are omitted, and the SIP Register message is forwarded to the S-CSCF identified by the information about the S-CSCF.

[0008] A processing device according to one aspect of the present invention is a processing device on which the Serving-Call Session Control Function (S-CSCF) of the Internet Protocol (IP) Multimedia Subsystem (IMS) is implemented, and comprises: receiving means for receiving a Session Initiation Protocol (SIP) Register message from a terminal device of a cellular communication system; and processing means for processing registration of the terminal device to the IMS, wherein the processing means does not contain S-CSCF information on which the terminal device has been registered by past registration processing in the SIP Register message, or in the IMS, IPsec (Security Architecture for Internet When Protocol is used, the registration process, which includes sending a Multimedia-Authentication-Request (MAR) message and receiving a Multimedia-Authentication-Answer (MAA) message, is performed with respect to the device that manages subscriber information relating to the terminal device in the cellular communication system. However, based on the fact that IPsec is not used in the IMS and the SIP Register message contains the S-CSCF 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 would be performed when IPsec is used.

[0009] According to the present invention, the processing load during registration of terminal devices for IMS communication in a cellular communication system can be reduced.

[0010] Other features and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings. In the accompanying drawings, the same or similar components are given the same reference numeral.

[0011] The attached drawings are included in the specification and constitute a part thereof, illustrating embodiments of the present invention and are used to explain the principles of the present invention together with their description. Figure 1A is a diagram showing an example of a system configuration. Figure 1B is a diagram showing an example of a system configuration. Figure 2 is a diagram showing an example of the flow of UE registration processing to IMS based on a conventional fourth-generation (4G) cellular communication system. Figure 3 is a diagram showing an example of the flow of UE registration processing to IMS based on a conventional fifth-generation (5G) cellular communication system. Figure 4 is a diagram showing a first example of the flow of UE registration processing to IMS according to this embodiment. Figure 5 is a diagram showing a second example of the flow of UE registration processing to IMS according to this embodiment. Figure 6 is a diagram illustrating roaming determination in Third Party Registration. Figure 7 is a diagram showing an example of processing performed in IMS. Figure 8 is a diagram showing an example of the hardware configuration of each device constituting the system. Figure 9 is a diagram showing an example of the functional configuration of a terminal device. Figure 10 is a diagram showing an example of the functional configuration of a device on which HSS or UDM / HSS is implemented. Figure 11 shows an example of the functional configuration of a device in which I-CSCF or S-CSCF is implemented.

[0012] 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.

[0013] (System Configuration) Figures 1A and 1B show examples of the configuration of the wireless communication system according to this embodiment. Figure 1A shows the configuration of a system that combines a fourth-generation (4G) cellular communication system with an Internet Protocol (IP) Multimedia Subsystem (IMS). Figure 1B shows the configuration of a system that combines a fifth-generation (5G) cellular communication system with an IMS. Note that Figures 1A and 1B 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 or functions that have similar functions to 4G and 5G in 6G and later cellular communication systems. Each of the functions shown in Figures 1A and 1B may be implemented by separate processing units, or multiple functions may be implemented by a single processing unit. Furthermore, a single function may be implemented by multiple processing units.

[0014] In this embodiment, a communication service using IMS (e.g., an IP-based voice communication service) is provided to a 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 of Figure 1A.

[0015] For example, when the UE is powered on or moves from outside the service area into the service area, it sends an Attach Request to the Mobility Management Entity (MME) via the base station (eNodeB) (S201). 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 registration (attachment) of the UE to the cellular communication system. After completing registration with the cellular communication system, the UE sends a message to the IMS via eNodeB, Serving Gateway (SGW), and Packet data network Gateway (PGW) to register with the IMS. The UE then sends a Session Initiation Protocol (SIP) Register message (S203).

[0016] 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). As a result, the I-CSCF confirms that the UE that sent the SIP Register is a legitimate UE registered with the HSS, and forwards the SIP Register message to the Serving-CSCF (S-CSCF) selected by the HSS to register the UE (S207). When S-CSCF receives a SIP Register message, it sends a Multimedia Authentication Request (MAR) to HSS to obtain information for the UE's authentication process (S208). Upon receiving the MAR, HSS issues the information necessary for authentication and sends it to S-CSCF in a 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 includes RAND, AUTN, XRES, Ck, and Ik in the MAA and sends it to the S-CSCF.

[0017] 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 a value calculated using the received RAND and long-term key Ki with a value derived from AUTN. UE also calculates Ck, Ik, and the response value RES. The UE then sends a SIP Register containing the RES to the 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 containing the RES to the S-CSCF (S217). The S-CSCF determines that the UE has been successfully authenticated by confirming that the received RES matches the XRES received in S209, and registers the UE with the IMS. Subsequently, S-CSCF sends a Server-Assistant-Request (SAR) to HSS (S218) to notify HSS that the UE has been registered. HSS then sends a Server-Assistant-Answer (SAA) to S-CSCF (S219) to notify S-CSCF of the UE's user profile. S-CSCF then notifies the UE via I-CSCF and P-CSCF that the series of processes has been completed (S220).

[0018] Furthermore, the flow of the UE's registration process to the cellular communication system and IMS in the system shown in Figure 1B is the same as in Figure 2, except that the MME and HSS in Figure 2 are replaced with Access and Mobility Management Function (AMF) and Unified Data Management (UDM) / HSS, respectively (and the corresponding message names, etc.). In other words, in steps S301 to S320 in Figure 3, processing is performed with the same intent as in steps S201 to S220 in Figure 2.

[0019] As shown in Figures 2 and 3, when a UE registers with the IMS, the I-CSCF and S-CSCF frequently access the HSS (or UDM / HSS). This process occurs every time the UE leaves the network (for example, by moving out of range or powering off) and then returns (for example, by moving back into range or powering on). As a result, the HSS (or UDM / HSS) may become overloaded due to the registration of the UE with the IMS, potentially degrading the overall network performance. In this embodiment, in view of these circumstances, a technique is provided to suppress the increase in load on the HSS (or UDM / HSS).

[0020] (Processing Example 1) Figure 4 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 the same procedure can be applied to subsequent standards. In this processing example, the same reference numerals are used for the same processes as in Figure 2, and their detailed explanations are omitted.

[0021] In this example, when the HSS receives a registration request from a UE to 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 each UE registered in an S-CSCF. 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 S-CSCF information, 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 or 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.

[0022] If the HSS is unable to obtain S-CSCF information, it notifies the UE that registration to 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 S-CSCF information, it transmits 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 transmit 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 information about the S-CSCF in which the UE is registered (and, if necessary, data to prevent tampering). Additionally, a new message from HSS to MME may be defined.

[0023] The MME may extract information about the S-CSCF in which the UE is registered (and, if necessary, tamper-proof data) 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. In one 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, tamper-proof data). 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). Note that 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). In addition, a new message from MME to UE may be defined.

[0024] 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, the UE may perform the Tracking Area Update procedure for location registration by moving across the 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, in one example, a new IE may be added to the TAU Accept message. For example, if an MME takes over the management of a UE that was previously managed by another MME, the MME will send a notification to the HSS regarding that UE. In response to this notification, the HSS will update the UE's registration information and, as described above, may also notify the HSS of the S-CSCF information (and, if necessary, tamper-proof data) to which the UE is registered. 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 an MME where IMS communication services are provided. When the UE enters the second area from the first area, the HSS may notify the UE via the MME of the S-CSCF information (and, if necessary, tamper-proof data) that was registered when the UE previously stayed in the second area, as described above.

[0025] 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 (I-CSCF and S-CSCF via P-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 S-CSCF information (and, if received, tamper-proof data) in the Authorization header of the SIP Register message and send it to the IMS.

[0026] 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 is included 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.

[0027] 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 registered by the UE is data issued by the HSS (i.e., tamper-proof). In one example, a conventional electronic signature mechanism may be used for tamper prevention. 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 may be used as tamper-proof data. This value is sent to the IMS via the UE, and the P-CSCF / I-CSCF decrypts the value using its private key and determines 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, P-CSCF / I-CSCF treats the information in the S-CSCF where the UE is registered as valid information if the validity period contained 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, P-CSCF / I-CSCF determines that the information in the S-CSCF where the UE in the SIP Register message is registered is invalid, and can perform the conventional processing without omitting the sending and receiving of UAR / UAA, as shown in the processing in Figure 2.

[0028] 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, a data specification such as JWT (JSON Web Token) (RFC7519) may be used to store S-CSCF information (address and FQDN (Fully Qualified Domain Name)) and MAC value. However, these are just examples, and other tamper-proof data or data specifications may be used.

[0029] As described above, in this process, the processing of S404, S405, S414, and S415 is omitted, thus reducing the load on the HSS. The I-CSCF identifies the S-CSCF in 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 in which the UE is registered (and, if received, data for preventing tampering), 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). Furthermore, 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 this case, the information of the S-CSCF in which the UE is registered (and, if received, data for preventing tampering) may be deleted. Also, the SIP Register message forwarded to the S-CSCF may have the 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 the conventional information. As explained in this example, if a SIP Register message containing information about the S-CSCF in which the UE is registered (and, if received, data for preventing tampering) is sent to the S-CSCF, the S-CSCF may ignore that information and proceed with its conventional processing.

[0030] 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.

[0031] The subsequent processing is the same as in the conventional process (S218-S220). As described above, in this processing example, the amount of signaling between I-CSCF and HSS can be reduced, and in particular the load on HSS can be reduced. 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.

[0032] (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 in the same procedure to subsequent standards. 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 transmitted with the new information described below included.

[0033] 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 selection information for 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 transmitting and receiving UAR and UAA, or a node other than the HSS may perform the selection of S-CSCF.

[0034] 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 the MAR or receive the MAA (S504, S505), and consequently, the subsequent processing (S506 to S513) is also omitted. Note that if IPsec is used, the processing in S504 to S513 is not omitted. In this case, I-CSCF may send the UAR and receive the UAA in S511 and S512, but this processing may be omitted depending on whether the processing in S205 and S206 has been performed. Furthermore, even if the processing in 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.

[0035] 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 the presence or absence of authentication information. The SIP Register message contains a P-Access Network Information (PANI) header, and the PANI header contains the Mobile Country Code (MCC) and the Mobile Network Code (MNC). By checking this PANI header, S-CSCF can determine whether a UE is roaming out. 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. In addition, this determination may be made in I-CSCF, in which case processes S205 and S206 may always be executed for UEs that are roaming out, and processes S205 and S206 may be omitted for UEs that are not roaming out (i.e., staying on the home network) and are the source UEs that send SIP Register messages containing certification information.

[0036] 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 by verification 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 been registered with the cellular communication system.

[0037] Furthermore, in one example, if a UE is configured to send SIP Register messages only when it is registered with a 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 the transmission of the MAR and the reception of the MAA, as well as the subsequent series of processing. However, even in this case, if IPsec is used, these processing will not be omitted. Also, when I-CSCF receives a SIP Register message, it may assume that the sending UE is registered with the HSS and omit the processing of sending the UAR and receiving the UAA. Furthermore, S-CSCF and I-CSCF may determine whether the UE is accessing the cellular communication system by checking the access type (access-type or access-class) in the PANI header of the SIP Register message. That is, 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 SIP Register messages 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 confirms that the UE is not roaming out and is certain 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 or not to omit the transmission and reception of MAR / MAA and subsequent processing (including the transmission and reception of SAR / SAA in some cases) based solely on the roaming determination.

[0038] Furthermore, the information in the PANI header of the SIP Register message is set by the UE, and therefore may not be valid. For this reason, for example, the HSS may include information about the UE's local network in the SAA, which is a 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 it is determined that the UE that sent the SIP Register message is not roaming out based on both, registration with the IMS may be performed using a omitted procedure. That is, for example, the S-CSCF may omit the steps S504 to S513 based on the information in the PANI header, and then send the SAR (S514) and receive the SAA (S515). Then, S-CSCF verifies that the UE has not roamed 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 processing without registering that UE with IMS.

[0039] Furthermore, after the processing shown in Figure 5, in which some processing is omitted based on the contents of the PANI header, Third Party Registration processing may be performed, for example as shown in Figure 6, so that the Telephone Application Server (TAS) performs UE roaming determination with the HSS. The S-CSCF sends a SIP REGISTER to the TAS, and in response to receiving the SIP REGISTER, the TAS sends a User-Data-Request to the HSS to make a query. The HSS then responds to receiving 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), which contains the PLMN-ID, a combination of MCC and MNC. Therefore, the TAS can determine whether the UE is within the home network (i.e., whether it is roaming out) based on the PLMN-ID. The TAS can then include this determination result in a SIP 200 (REGISTER) and transmit it to the S-CSCF. Note that the SIP 200 (REGISTER) may also contain information on the ECGI and PLMN-ID, and the roaming determination may be performed at the S-CSCF. Furthermore, if S-CSCF determines that a UE is roaming out in this determination, it may determine that the SIP Register message was not a legitimate request from that UE because it contradicts the contents of the PANI header, and may perform error processing without registering that UE with IMS.

[0040] Figure 7 shows an example of the processing flow performed by IMS in this example. Note that this is just one example, and 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 of the processing may be performed by other functional units 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.

[0041] First, when S-CSCF receives a SIP Register message, it 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 and determines whether the UE is roaming out (S702). In other words, S-CSCF determines whether the UE is located within the home network. If the UE is roaming out (located on a different network than the home network) (YES in S702), S-CSCF executes the conventional IMS registration process as shown in Figure 2 (S704) and then terminates the process.

[0042] If the UE is not roaming out (is within the home network) (NO in S702), S-CSCF omits the processing in S504 to S513, as explained in relation to Figure 5 (S703). Then, S-CSCF transmits 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 in S220, it performs Third Party Registration and determines whether the UE is roaming out or not through information exchange between TAS and HSS (S706). Then, 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 registers the UE with IMS and terminates the process. On the other hand, if S-CSCF determines in S705 and S706 that the UE is roaming out (is in a network different from the home network) (YES in S705 or S706), it performs error processing (S707) because it contradicts the determination result in S702, and terminates the process without registering the UE with IMS.

[0043] 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 registration has been completed. This reduces the processing load related to UE registration with IMS, particularly the processing load on HSS.

[0044] As described above, each of the processes described is applicable in a cellular communication system that succeeds 4G, such as 5G. However, for such application, non-substantive changes such as the name of the message are made. For example, the above-mentioned 4G Attach Request / Attach Accept can be replaced with Registration Request (Initial Registration) / Registration Accept in 5G. Also, the above-mentioned 4G Tracking Area Update Request / Tracking Area Update Accept can be replaced with Registration Request (Mobility Registration Update) / Registration Accept in 5G. Also, the above-mentioned 4G Update Location Request / Update Location Answer can be replaced with Nudm UE CM Registration Request / Nudm UE CM Registration Response in 5G. Note that Nudm UE CM Registration may be denoted as Nudm UE ContextManagement. Thus, although the name of the message may differ depending on the generation of the cellular communication system, by performing the above-described information exchange in corresponding messages with the same purport, it is possible to reduce the processing load on nodes having a function of managing subscriber information, such as HSS and UDM / HSS, and the load on the entire network.

[0045] (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 the ROM 802 and storage device 804. The ROM 802 is a read-only memory that stores information such as programs and various parameters related to the processing executed by each device. The RAM 803 functions as a workspace when the processor 801 executes programs and is a random access memory that stores temporary information. The 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 communication described above. Although one communication circuit 805 is shown in Figure 8, each device may have multiple communication circuits.

[0046] Figure 9 shows an example of the functional configuration of a terminal device that functions as a 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.

[0047] The information acquisition unit 901 acquires, for example, the above-described information (information on the S-CSCF (and anti-tampering data) registered by past registration processing and certification information for proving that it is registered in the cellular communication system) from the HSS or UDM / HSS that manages the subscriber information of the terminal device in the cellular communication system via the MME or AMF. The information acquisition unit 901 can acquire the above-described information, for example, by transmitting request information for registration requests to the cellular communication system, tracking area updates, and the like. The IMS registration request unit 902 transmits the information acquired by the information acquisition unit 901 to the IMS (P / I / S-CSCF) included in the SIP Register message.

[0048] FIG. 10 shows a functional configuration example of a processing device in which the functions of the above-described HSS or UDM / HSS are implemented. The processing device includes, for example, a UE management unit 1001, a registration state determination unit 1002, and an information providing unit 10'03. These functional units can be realized, for example, when the processor 801 executes programs stored in the ROM 802 and the storage device 804. Further, these functional units may be implemented in the communication circuit 805. In FIG. 10, only the functional configuration of the HSS or UDM / HSS related to the present embodiment is illustrated, and it naturally has the functions as the HSS or UDM / HSS of a normal cellular communication system. Further, the processing device only needs to have functions related to at least any one of the above-described embodiments, and some of the functions shown below may be omitted.

[0049] The UE management unit 1001 manages subscriber information of 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 processing. 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 the MME or AMF) once the information has been obtained. The information provision unit 1003 may also generate tamper-proof data to prevent tampering with the S-CSCF information and provide it to the UE as needed.

[0050] 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.

[0051] 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 processing, 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. The information extraction unit 1101 also extracts certification information if it is included in the SIP Register message indicating that authentication has been performed for registration with the cellular communication system by the UE. 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.

[0052] 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.

[0053] 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 processing. Also, if the above-mentioned proof information is extracted and, for example, the processing in S504 to S510 in Figure 5 is 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 proof information is extracted, the I-CSCF processing execution determination unit 1102 may execute the conventional processing without omitting any processing. 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 processing in S205 and S206 of Figure 5. Also, the I-CSCF processing execution determination unit 1102 may determine, for example, that the UE is not roaming out based on the information in the PANI header of the SIP Register message, and then determine to perform the same processing as when certification information is extracted.

[0054] 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, for example, the PANI header information in the SIP Register message indicates that the UE is not roaming out and IPsec is not used, the S-CSCF processing execution determination unit 1102 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. Furthermore, 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.

[0055] The registration processing unit 1103 executes the process that the processing execution determination unit 1102 has determined to execute. In the case where the processes S504 to S513 are omitted in Figure 5, if 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. Also, in the case where the processes S504 to S513 are omitted in Figure 5, if the registration processing unit 1103 determines that the UE is roaming out in the Third Party Registration after the processing in S220, it may discard the information related to the registration process up to that point and execute error processing.

[0056] As described above, the cellular communication system and IMS according to this embodiment are configured to omit some of the processing that was previously 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 related to 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."

[0057] 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.

[0058] This application claims priority based on Japanese Patent Application No. 2025-010624, filed on 24 January 2025, and all of its contents are incorporated herein by reference.

Claims

1. A terminal device for a cellular communication system, comprising: an acquisition means for acquiring information of the Serving-Call Session Control Function (S-CSCF) of an Internet Protocol (IP) Multimedia Subsystem (IMS) to which the terminal device is registered through past registration processes, from a device that manages subscriber information relating to the terminal device in the cellular communication system; and a transmission means for including the information in a Session Initiation Protocol (SIP) Registerer message for registration to the IMS and transmitting it to the IMS.

2. The terminal device according to claim 1, wherein the acquisition means further acquires data for preventing tampering with the S-CSCF information from the device that manages the subscriber information.

3. The terminal device according to claim 1, wherein 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 S-CSCF 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 S-CSCF 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 a terminal device in a cellular communication system, comprising: determination means for determining whether there exists a Serving-Call Session Control Function (S-CSCF) of an Internet Protocol (IP) Multimedia Subsystem (IMS) in which the terminal device is registered through past registration processing; and providing means for providing information of the S-CSCF to the terminal device if such an S-CSCF exists.

6. The processing apparatus according to claim 5, wherein the providing means further provides data to the terminal device for preventing tampering with the information of the S-CSCF.

7. The processing apparatus according to claim 5, wherein the providing means, upon receiving a message requesting registration of the terminal device with the cellular communication system, provides the S-CSCF information to the terminal device in a message in response to the request.

8. The processing device according to claim 5, wherein 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, and the providing means provides the S-CSCF information to the terminal device via a fourth-generation Mobility Management Entity (MME) when the processing device is the HSS, or via a fifth-generation Access and Mobility Management Function (AMF) when the processing device is the UDM / HSS.

9. A processing device on which the Interrogating-Call Session Control Function (I-CSCF) of the Internet Protocol (IP) Multimedia Subsystem (IMS) is implemented, comprising: receiving means for receiving a Session Initiation Protocol (SIP) Register message from a terminal device of a cellular communication system; and processing means for processing registration of the terminal device to the IMS, wherein the processing means is the SIP A processing device that, if the Register message does not contain information about an S-CSCF to which the terminal device is registered through past registration processing, sends a User-Authorization-Request (UAR) message and receives a User-Authorization-Answer (UAA) message to a device that manages subscriber information related to the terminal device in the cellular communication system, and forwards the SIP Register message to the S-CSCF identified by the UAA; and, based on the fact that the SIP Register message contains information about the S-CSCF, omits sending the UAR message and receiving the UAA message, and forwards the SIP Register message to the S-CSCF identified by the information about the S-CSCF.

10. The processing apparatus according to claim 9, wherein the SIP Register message further includes data for preventing tampering with the S-CSCF information, and the processing means omits sending the UAR message and receiving the UAA message when the S-CSCF information that has not been tampered with is included in the SIP Register message, and does not omit sending the UAR message and receiving the UAA message when the S-CSCF information is included in the SIP Register message but is not determined to be tampered with.

11. The processing device according to claim 9, wherein, in the case where IPsec (Security Architecture for Internet Protocol) is used in the IMS and the transmission of the UAR message and the reception of the UAA message are omitted, the processing means further omits the transmission of a second UAR message and the reception of a second UAA message corresponding to a second SIP Register message received from the terminal device in the authentication process performed when using IPsec.

12. A processing device on which the Serving-Call Session Control Function (S-CSCF) of the Internet Protocol (IP) Multimedia Subsystem (IMS) is implemented, comprising: receiving means for receiving a Session Initiation Protocol (SIP) Register message from a terminal device of a cellular communication system; and processing means for processing registration of the terminal device to the IMS, wherein the processing means does not contain S-CSCF information in which the terminal device has been registered by past registration processing in the SIP Register message, or in the IMS, IPsec (Security Architecture for Internet A processing device that, when Protocol is used, performs the registration process, 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, and performs the registration process, which omits sending the MAR message and receiving the MAA message, and omits the authentication process that would be performed when IPsec is used, based on the fact that IPsec is not used in the IMS and the SIP Register message contains the S-CSCF information.

13. A control method performed by a terminal device of a cellular communication system, comprising: obtaining information of the Serving-Call Session Control Function (S-CSCF) of an Internet Protocol (IP) Multimedia Subsystem (IMS) to which the terminal device is registered by past registration processing, from a device that manages subscriber information relating to the terminal device in the cellular communication system; and transmitting the information to the IMS in a Session Initiation Protocol (SIP) Registerer message for registration to the IMS.

14. A control method performed by a processing device that manages subscriber information relating to a terminal device in a cellular communication system, comprising: determining whether there is a Serving-Call Session Control Function (S-CSCF) of an Internet Protocol (IP) Multimedia Subsystem (IMS) to which the terminal device is registered by past registration processing; and, if an S-CSCF to which the terminal device is registered exists, providing the information of the S-CSCF to the terminal device.

15. A control method executed by a processing device on which the Interrogating-Call Session Control Function (I-CSCF) of the Internet Protocol (IP) Multimedia Subsystem (IMS) is implemented, comprising: a receiving step of receiving a Session Initiation Protocol (SIP) Register message from a terminal device of a cellular communication system; and a processing step of registering the terminal device with the IMS, wherein in the processing step, the SIP A control method comprising: if the Register message does not contain information about an S-CSCF to which the terminal device is registered through past registration processing, sending a User-Authorization-Request (UAR) message and receiving a User-Authorization-Answer (UAA) message to a device that manages subscriber information related to the terminal device in the cellular communication system, forwarding the SIP Register message to the S-CSCF identified by the UAA, and, based on the fact that the SIP Register message contains information about the S-CSCF, omitting the sending of the UAR message and the receiving of the UAA message, and forwarding the SIP Register message to the S-CSCF identified by the information about the S-CSCF.

16. A control method executed by a processing device on which the Serving-Call Session Control Function (S-CSCF) of the Internet Protocol (IP) Multimedia Subsystem (IMS) is implemented, comprising: a receiving step of receiving a Session Initiation Protocol (SIP) Register message from a terminal device of a cellular communication system; and a processing step of registering the terminal device with the IMS, wherein in the processing step, if the SIP Register message does not contain information about the S-CSCF to which the terminal device has been registered by past registration processing, or if the IMS does not contain IPsec (Security Architecture for Internet A control method that, when Protocol is used, performs the registration process, 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, and, based on the fact that IPsec is not used in the IMS and the SIP Register message contains the S-CSCF information, omits sending the MAR message and receiving the MAA message, and performs the registration process, omitting the authentication process that would be performed when IPsec is used.

Images