IMS Server Re-Selection Using Subscriber-Assisted Session Control
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Solution Overview
Problem
The legacy Cx S-CSCF re-selection procedure in IMS over SBI may lead to disruptions and failed sessions due to the inability to ensure that S-CSCF re-selection requests are coming from an I-CSCF, violating stateless interaction principles and resulting in higher risks of failed sessions.
Innovation Solution
A method where a first IMS node selects a second server for session control by receiving selection assistance data and sending an indication to a subscriber server to register the second server's address, allowing efficient server replacement with minimal signaling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a user equipment is roamed from a GSM network to a UMTS network, then the user can access services in the UMTS network, but the user equipment does not have an IMSI number in the HSS of the home PLMN and cannot be identified by the HSS, causing inability to access IMS services
Solution Approach 1:
The patent introduces a PGW eHRFD as an intermediary component between the UMTS network and the HSS. This PGW eHRFD stores the IMSI number of the user equipment and provides it to the CSCF when needed, enabling the HSS to identify and authenticate roaming users who don't have local IMSI storage in the home PLMN's HSS.
Solution Approach 2:
The patent extends the identification mechanism by adding a new dimension - storing and retrieving IMSI numbers from the PGW eHRFD in the home PLMN's network infrastructure. This additional storage dimension allows the system to resolve identification issues for roaming users without affecting the existing UMTS network operation.
2Adaptability or versatility
If the user equipment uses a roaming IP address from the visited PLMN, then the user can connect to the visited network, but the user cannot access services in the home PLMN's IP Multimedia Subsystem due to identification failure
Solution Approach 1:
The patent implements a feedback mechanism where the PGW eHRFD receives identification requests from the CSCF, queries the stored IMSI numbers using the user's identifier, and returns the appropriate IMSI number. This feedback loop enables successful authentication and service access for roaming users by providing the missing identification information.
Solution Approach 2:
The patent performs preliminary action by pre-storing the IMSI numbers of user equipment in the PGW eHRFD before roaming occurs. This advance preparation ensures that when a user equipment roams to the UMTS network, the identification information is already available, eliminating authentication delays or failures.
3Ease of operation
If the HSS tries to identify the user equipment using the roaming IP address, then the identification process can proceed, but the HSS cannot find the user's IMSI number because it is not stored in the visited PLMN's HSS
Solution Approach 1:
The patent positions the PGW eHRFD as a mediator that bridges the gap between the CSCF's identification request and the actual IMSI number storage. When the CSCF queries for user identification, the PGW eHRFD intercepts the request, retrieves the IMSI number from its stored data using the user's identifier, and provides it to the CSCF, ensuring successful identification without requiring the HSS to have local IMSI storage.
Data Source
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AI summary
A method performed by a first IMS node for handling a setup of a session for communication with a User Equipment (UE) in a communications network is provided.The UE is assigned a first server for session control of the session,. The first IMS node sends (203) a request to a subscriber server associated with the UE. The request requests assistance data for selecting a second server to be assigned to the UE for the session control. The first IMS node selects (205) a second server to be assigned to the UE for session control, based on the requested assistance data when received from the subscriber server. The first IMS node sends (206) an invitation to the selected second server. The invitation relates to the setting up the session. The invitation comprises an indication indicating that the selected second server is selected to replace the first server. The indication triggers the selected second server, to indicate to the subscriber server to register the address of the selected second server in the subscriber server, to replace the first server in being assigned to the UE for the session control. The indication permits the subscriber server, to perform the registering to replace the first server with the selected second server to be assigned to the UE for session control for said session.