SRVCC Handover Voice Continuity via HLR/HSS Correlation
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Solution Overview
Problem
Voice call continuity is disrupted during handovers between LTE (E-UTRAN) and UTRAN/GERAN networks due to the inability to maintain voice over PS core network, leading to potential call interruptions during Single Radio Voice Call Continuity (SRVCC) procedures.
Innovation Solution
Implementing a Mobility Management Entity (MME) and Serving GPRS Support Node (SGSN) that register correlations between user equipment (UE) and nodes in the Home Location Register/Home Subscriber Server (HLR/HSS) to ensure seamless handovers between packet switched (PS) and circuit switched (CS) domains, allowing proper node location and mobility management transfer even if initial attempts fail.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If SRVCC handover is performed from E-UTRAN to UTRAN/GERAN, then voice service continuity is maintained between IMS over PS access and CS access, but voice call interruption occurs during the handover process
Solution Approach 1:
The MME performs a location update procedure in the HLR/HSS before the SRVCC handover is triggered. This preliminary action ensures that the HLR/HSS has current information about the UE's serving MME, so that when the SRVCC handover occurs, the SGSN can successfully retrieve the UE context from the HLR/HSS without causing call interruption.
2Loss of energy
If the MME deletes UE information after timer expiration, then network resources are freed, but the SGSN cannot retrieve UE context causing RAU rejection
Solution Approach 1:
The location update is performed in advance before the timer expires and before SRVCC handover is needed. This ensures the HLR/HSS has up-to-date MME information without requiring the MME to extend its timer, thus freeing resources while maintaining handover reliability.
Solution Approach 2:
The HLR/HSS acts as an intermediary that stores the correlation between UE and serving MME. By updating the HLR/HSS in advance, the system ensures that even if the MME deletes local UE information, the SGSN can still retrieve the correct MME identity from the HLR/HSS to obtain UE context.
3Adaptability or versatility
If PS handover occurs from MME 10 to MME 40, then voice call remains active during mobility, but the MME 10 deletes UE information causing context retrieval failure
Solution Approach 1:
The HLR/HSS serves as a central intermediary that maintains the UE-MME correlation information. When MME 10 performs PS handover to MME 40, the HLR/HSS is updated with the new MME 40 information. This ensures that subsequent SRVCC handover requests can successfully retrieve UE context through the HLR/HSS, preventing information loss.
Solution Approach 2:
The location update procedure is executed in advance after PS handover but before SRVCC handover. This preliminary update ensures the HLR/HSS contains the current serving MME information, preventing context retrieval failure during subsequent handover operations.
Data Source
AI summary
A handover of a user equipment (UE) between different radio access networks (RANs). For enhancing voice call continuity (VCC). One method comprises: receiving a request for registering in a first node for mobility management in the target RAN from the UE; if the mobility management for the UE fails to be transferred from a second node for mobility management in the source RAN to the first node, inquiring of a HLR/HSS about a third node for mobility management for the UE in the source RAN, wherein the second node is determined from the request for registering, and the third node is determined based on a correlation between the UE and the third node; and sending to the third node a request for transferring the mobility management for the UE from the third node to the first node.