Hello everyone,
I want to discuss a specific scenario related to the Handover between VoWiFi to VoLTE in a 5G coverage. We have a smartphone who supports a VoWiFi and VoLTE, but he doesn’t support the VoNR.
So, let’s imagine the scenario that we are in a 5G coverage, enable the VoWiFi and start a call. When the user starts to move, he will lose the Wi-Fi signal and the call must handover to VoLTE. However, we are seeing some problems on this scenario, when the mobile loses the signal from wifi he tries to connect to the 5G again and the call droped.
I want to understand better the flow for this scenario and why the correct HO for VoLTE doesn’t happen.
I assume 5G EN_DC. In that case you better check that VoLTE is working for a UE in 5G-ENDC connected mode.
Hi,
This is a very common issue when youare deploying 5G SA initially as well as VoNR and this is called cross procedure.So when the subscriber is trying to move from one coversge area to another it wont have to change the Core node Ideally you If you have a dual mode core.If not then you have to which can trigger a TAU .But for the handover that wont be an issue,But in UE there is a behaviour called "Cross procedure "where when UE trying to establish a new PDN connection,Lets say 5G if in the middle of it if 4G requests a new procedure UE will abandon the old one and start a new 4G procedure.So this will make the call setup up time longer and eventually disconnection as well.Therefore when doing the testing you need to adjust some timers in the network like T409 which is retry timer so handset will try not loos the pdn flow.For wifi call there is another issue in Ericsson WMG and PCG which they have fixed in a later LCM cycle which is VoWIFI to VoNR handover is not working as a workaround you need to set implicit unsubscription feature in HLR so UE will select volte instead.Thank you
2 Likes