SRVCC Resume Signalling for PS Service Continuity
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Solution Overview
Problem
The existing Single Radio Voice Call Continuity (SRVCC) function collides with Idle Mode Signalling Reduction (ISR), leading to lost packet services and voice services when user entities move between LTE and 2G/3G networks, especially in non-Dual Transfer Mode (DTM) scenarios, as the UE may not resume PS services after a CS voice call, resulting in discarded incoming packets and lack of paging.
Innovation Solution
A method is introduced where the Mobile Control Node (MCN) and Mobile Switching Centre (MSC) exchange specific signalling messages to explicitly or implicitly resume PS services after a CS voice call is dropped, ensuring the UE can re-establish packet services, even if it was in a suspended mode or not sending RAU/TAU signals, by using SRVCC CS to PS resume requests and responses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the UE moves between LTE and 2G/3G networks using ISR (Idle Mode Signalling Reduction), then signalling overhead is reduced and mobility is improved, but the UE may not resume PS services after a CS voice call, causing lost packet services and discarded incoming packets
Solution Approach 1:
The network performs preliminary actions by sending a SRVCC CS to PS Resume Request message to the MCN before the UE needs to resume services. The MCN then sends an explicit or implicit resume message to the PGW/SGW in advance, ensuring the PS service is resumed before the UE attempts to access it, preventing packet loss.
Solution Approach 2:
The system implements feedback through the SRVCC CS to PS Resume Request message flow. The MSC detects when a CS call ends and provides feedback to the MCN, which then triggers the resume procedure with the PGW/SGW, ensuring the network is aware of and responds to the UE's service resumption needs.
2Device complexity
If the UE stays in IDLE mode between LTE and 2G/3G without sending RAU/TAU signals, then signalling overhead is reduced, but the network is not aware of the UE's location and cannot resume PS services or perform paging
Solution Approach 1:
The invention introduces an intermediary mechanism where the MSC acts as a mediator between the UE and the core network. When the CS call ends, the MSC sends a SRVCC CS to PS Resume Request message to the MCN, which then triggers the resume procedure with PGW/SGW, allowing service resumption without requiring the UE to actively signal its presence.
3Loss of time
If the UE reselects to the same LTE cell after a CS call without performing TAU, then power consumption is reduced and access latency is minimized, but the network remains unaware of the UE's return and cannot restore PS services
Solution Approach 1:
The network performs preliminary actions by maintaining state information in the MCN and PGW/SGW nodes. When a CS call ends, the MSC triggers a resume request to the MCN, which has already prepared the network to quickly restore PS services without requiring the UE to perform a full TAU procedure, thus reducing access latency while ensuring service restoration.
Data Source
AI summary
A method for a Mobile Control Node, MCN, supporting handover of a packet switched, PS, voice call of a given user entity anchored in a IP Multimedia Subsystem (IMS) to a circuit switched, CS, voice call, by using a Single Radio Voice Call Continuity, SRVCC, function, whereby, - after handover from PS to CS (102) voice call pertaining to a user entity, UE, which UE is in a suspended mode (305, 206/209/303), and upon receiving a SRVCC CS to PS resume request message (107) from a mobile switching centre, MSC, - issuing an explicit / implicit resume message (109, 306) to a packet gateway (PGW) node or a serving gateway (SGW) node, causing the UE to resume PS services (110). Further a method for a Mobile Switching Centre (MSC) supporting handover of a packet switched, PS, voice call of a given user entity (UE) via an SP Multimedia Subsystem (IMS) to a circuit switched, CS, voice call, by using a Single Radio Voice Call Continuity, SRVCC, function, wherein - after handover from PS to CS (103), and after detecting hang up or dropped call (106) issuing (209) a SRVCC CS to PS resume request message (107) to a MCN, thereby effecting the user entity to resume PS services of the voice call for a given user entity (UE).