IMS Session Continuity via MSC-Assisted Transaction Identifiers
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Solution Overview
Problem
IMS Centralized Services face challenges in managing sessions when a user terminal moves from a network supporting simultaneous IP data transport and circuit-switched calls to one that does not, leading to loss of held sessions due to the inability to use Gm signaling for session management.
Innovation Solution
The Service Centralization and Continuity Application Server (SCC AS) requests the Mobile Switching Center (MSC) server to inform it about the access network used by the user terminal and its ability to support simultaneous IP data and circuit-switched calls, triggering MSC server-assisted mid-call features and creating transaction identifiers for held sessions, while the user terminal also creates corresponding identifiers, ensuring session preservation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the user terminal moves to a GERAN network without DTM support, then the circuit-switched call can be maintained, but IP data transport must be suspended and Gm signaling cannot be used for session management
Solution Approach 1:
The MSC server acts as an intermediary between the circuit-switched call and the IMS session management system. It creates transaction identifiers that allow the SCC AS to manage ICS sessions even when Gm signaling is unavailable, effectively mediating between the legacy circuit-switched domain and the IMS packet-switched domain
Solution Approach 2:
The session management function is segmented into two parts: Gm signaling for normal operation and MSC server-assisted mid-call features with transaction identifiers for GERAN without DTM operation. This segmentation allows the system to use different management mechanisms depending on the network condition
2Ease of operation
If Gm signaling is used for session management, then ICS sessions can be managed seamlessly, but the terminal must be able to simultaneously transport IP data and maintain circuit-switched calls
Solution Approach 1:
The system changes the operational parameters based on network capability. When DTM is available, Gm signaling is used; when DTM is not available, the system switches to MSC server-assisted mid-call features with transaction identifiers, effectively adapting the session management parameters to the network conditions
3Use of energy by moving object
If the terminal is transferred to a network without simultaneous IP and circuit-switched support, then radio resource efficiency is improved, but held sessions are lost due to inability to use Gm signaling
Solution Approach 1:
The MSC server preliminarily creates transaction identifiers for held sessions before the terminal is transferred to GERAN without DTM. This preliminary action ensures that session state information is preserved and can be recovered after transfer, preventing loss of held sessions
Solution Approach 2:
The system implements feedback mechanisms where the SCC AS receives notifications about network conditions and terminal capabilities, then adjusts session management accordingly. The MSC server provides feedback about held sessions using transaction identifiers, allowing the SCC AS to maintain awareness of session state even without Gm signaling
Data Source
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AI summary
Techniques for managing multiple ICS sessions in an IMS network are described. In one method, a MSC server detects that a user terminal has been transferred from a first access network to a second access network and, in response, sends a message to an SCC AS, the message indicating transfer of the user terminal. The MSC server receives, in response, one or more requests for MSC server-assisted mid-call feature services for the user terminal, and assigns transaction identifiers to one or more sessions held for the user terminal or to one or more conference participants corresponding to the user terminal. Corresponding techniques carried out at an SCC AS are also described.