VoLTE Issues

HI Guys.
I have some issue with VoLTE.
Hope you can clarify on this questions.
It will be also useful if anyone have signaling flow end to to end which inter relate SIP, Radio and Core signals for call setup.

  1. Voice policy selection. Is it hard coded. Is it based on UE vendor. Is there UE model , which is flexible to choose voice policy selection
  2. At times, based on the log file, there are call drop at the IMS side but at the radio side, there is no call drop shown based on their KPI. What could be the reason that call drop detected at IMS but not shown in the call drop counter at radio side. I assume is either that the MME release the erab with cause: normal release because no cause code sent to MME or it is because IMS doesn’t inform MME when there is drop from IMS.
  3. When there is call setup failure or call drop in IMS, will the IMS domain Inform MME with cause code. If yes, will that be used by MME to trigger normal erab release or abnormal erab release
  4. Can we disable certain UE model of doing Volte call in the network?
  5. In some scenario. when UE couldn’t setup Volte call, the network redirect the UE to do CSFB. Does this happen because of the setting at the Core Network or it is based on UE type model
  6. How is the use experience when there is call drop happen in IMS?
  7. There are times, after call session, there no ‘deactivate EPS bearer from MME’ and the next call will be setup without deactivating the previous eps bearer. Suppose after a call, there should be eps bearer deactivation before new call setup.

Here’s a good call flow for VoLTE:

Note: you can find this and other flow in the blog listed in our Resources page Blogs/Docs from COMPANIES

Also here is a good picture with callflow for VoLTE with all IMS elements involved:

Hello Mate,
Any error cause from IMS side (with Bye or cancel message), coming from SBG to the UE, triggering Session abort message on Rx interface (SBG/P-CSCF and PCRF), then PCRF/SAPC will force the EPG/PGW to deactivate the EPS bearer, this will be considered as Normal release by the eNodeB .
for example SBG can trigger Call drop due to RTP Time out (Silent call detected), which will be counted as normal release by the eNodeB.
the ENodeB only counts drops due to Radio link failure or reestablishment failure.

Thanks a lot