Visited Access Transfer Function for Handover Delay
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Solution Overview
Problem
Current SRVCC solutions result in service delays due to SIP signaling being routed back to the home network and then to the remote end during session transfers, causing media path changes and poor service experiences for GSM/WCDMA subscribers in IMS networks.
Innovation Solution
Implementing a transfer functionality in the visited network, specifically using the Serving MSC Server to anchor media and route SIP messages to the correct MSC Server, allowing the SCC AS in the home network to manage access transfers and minimize delay by anchoring sessions in the Visited Access Transfer Function within the visited network.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If the SCC AS in the home network routes SIP signaling back to the home network during session transfer, then the IMS session can be managed centrally, but the handover delay increases and service continuity deteriorates
Solution Approach 1:
The patent introduces a Visited Access Transfer Function (VATF) as an intermediary entity in the visited network. The VATF acts as a local mediator that receives SIP signaling from the UE during handover and forwards it to the SCC AS, eliminating the need for signaling to route back through the home network. This intermediary resolves the contradiction by maintaining centralized management while reducing the signaling path length and handover delay.
Solution Approach 2:
The patent segments the session management functionality by separating the access transfer function (VATF) from the session control function (SCC AS). The VATF handles local access transfer signaling in the visited network, while the SCC AS maintains centralized session management. This segmentation allows the system to achieve both localized fast handover and centralized session control without the signaling round-trip delay.
2Reliability
If the media path is changed by routing SIP signaling through the home network to the remote end, then the IMS call can be transferred, but the service experience deteriorates due to poor continuity
Solution Approach 1:
The patent implements preliminary action by having the VATF prepare and process the SIP signaling locally during the handover process. The access transfer signaling is handled in advance by the VATF before the media path change is complete, ensuring that the signaling is already routed correctly when the handover occurs. This preliminary local processing ensures reliable call transfer while maintaining smooth service continuity without delays.
3Extent of automation
If the SCC AS anchors the session in the home network during roaming, then centralized control is maintained, but the handover performance worsens due to increased signaling distance
Solution Approach 1:
The VATF serves as a local intermediary that bridges the UE and the home network SCC AS during roaming. It receives and processes SIP signaling locally in the visited network, then forwards it to the SCC AS, eliminating the need for signaling to physically route back through the home network infrastructure. This maintains centralized session anchoring while dramatically improving handover execution speed by removing the signaling distance bottleneck.
Solution Approach 2:
The patent changes the signaling dimension by introducing a new signaling path through the VATF in the visited network. Instead of the traditional path that requires signaling to traverse back to the home network, the VATF creates a local signaling dimension that processes handover requests immediately and forwards them efficiently to the SCC AS, reducing the effective signaling distance and improving handover productivity.
Data Source
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AI summary
A method of anchoring a packet switched session of a subscriber comprises receiving a packet switched request for a session setup, and anchoring the packet switched session in a control node (MSC-S) of a visited network of the subscriber.