ATCF Media Anchoring for IMS Handover Delays
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Solution Overview
Problem
Current mechanisms for handover of voice calls from packet switched to circuit switched access in IMS architecture face delays and potential interruptions due to long signaling paths, especially when a user roams across different radio access technologies, leading to suboptimal handover control.
Innovation Solution
The introduction of an Access Transfer Control Function (ATCF) in the serving IMS network, which acts as a media gateway controller, delegates handover responsibilities from the Service Centralisation and Continuity Application Server (SCC AS) to the Access Transfer Gateway (ATGW), allowing local redirection of media during handovers and optimizing the handover process by anchoring media traffic within the visited network.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If handover control is centralized in the SCC AS in the home network, then service continuity is maintained, but handover delays increase and handover efficiency deteriorates
Solution Approach 1:
The patent segments the handover control function by introducing an Access Transfer Control Function (ATCF) in the visited network that handles local handover control, while the SCC AS in the home network retains responsibility for service continuity. This segmentation allows handover decisions to be made locally without waiting for centralized approval, reducing handover delay while maintaining service continuity through the coordinated architecture between ATCF and SCC AS.
Solution Approach 2:
The ATCF acts as an intermediary between the mobility management entity and the media gateway controller during handover. It receives handover requests from the mobility management entity, coordinates with the SCC AS for service continuity validation, and executes the media path switching. This intermediary role enables local handover control while maintaining the centralized service continuity management architecture.
2Reliability
If handover signaling path is lengthened to include home network SCC AS, then service continuity is ensured, but handover complexity and processing overhead increase
Solution Approach 1:
The signaling path is segmented into two parts: local handover control signaling between ATCF, mobility management entity, and media gateway controller in the visited network; and service continuity validation signaling between ATCF and SCC AS in the home network. This segmentation reduces the complexity of the overall handover process by allowing most signaling to be handled locally without involving the home network SCC AS for every handover event.
Solution Approach 2:
The ATCF performs preliminary handover control actions locally in the visited network, including receiving handover requests, selecting target media gateways, and executing media path switching. Only service continuity validation requires communication with the home network SCC AS. This preliminary local action reduces signaling complexity and processing overhead by handling the majority of handover procedures without home network involvement.
3Reliability
If media redirection is centralized in the home network, then service continuity is maintained, but handover speed and efficiency decrease
Solution Approach 1:
Media redirection functionality is segmented between the ATCF in the visited network and the SCC AS in the home network. The ATCF performs local media path switching and redirection by controlling media gateways in the visited network, while the SCC AS provides service continuity validation. This segmentation enables rapid local media redirection without waiting for home network processing, significantly improving handover speed while maintaining service continuity through coordinated architecture.
Solution Approach 2:
The ATCF serves as an intermediary that executes media redirection locally by controlling media gateways in the visited network. It receives service continuity validation from the SCC AS and then performs the actual media path switching without further home network involvement. This intermediary role enables fast local media redirection while maintaining the centralized service continuity management architecture.
4Productivity
If handover control is decentralized to the visited network ATCF, then handover efficiency improves, but coordination complexity between network functions increases
Solution Approach 1:
The ATCF is designed as a multi-functional node that combines mobility management interfaces, media gateway control capabilities, and service continuity validation coordination. It can handle handover requests from different radio access technologies, control multiple media gateways, and coordinate with the SCC AS using standardized interfaces. This multi-functionality reduces coordination complexity by consolidating multiple handover control functions into a single versatile node in the visited network.
Data Source
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AI summary
A method of enabling the management of handovers of voice calls from a Packet Switched, PS, access to a Circuit Switched, CS, access where the voice calls are established using an IP Multimedia Subsystem, IMS, network. The method comprises performing a first IMS registration of a user via said PS access including setting for the user in a Home Subscriber Server, HSS, of the user's home network, an identifier of a first access transfer control fu nction, which access transfer control function is responsible for anchoring user media sessions in an access transfer gateway of a serving network, and notifying a mobility function within said service network of the set identifier. A second or further IMS registration of the same user is then performed via said PS access, it being determined that said first IMS registration exists. As a consequence, the setting of an identifier of a second or further access transfer control function in the HSS for the user is prevented, whilst either the setting of the identifier of the first access transfer control function is maintained, or is replaced with an identifier of a service centralisation and continuity application server. The mobility function is notified of any change to the set identifier. In the event of a requirement to handover an ongoing voice call associated with said second or further IMS registration from said PS to said CS access, the identifier currently set in the HSS and identified to the mobility function is used to manage the handover.