If network send RRC connection release abnormally will UE send bye SIP message?

Hi Experts.

During ongoing VoLTE call, if network send RRC connection release abnormally will UE send bye SIP message and drop call?

What will be scenario here?

In this scenario UE will not have chance to send bye, because default bearer used for signalling (qci5) will be torn down.

PGW will send ccr-t towards PCRF.

And PCRF will send ASR to SBC.

Upon ASR SBC will trigger BYE towards UE and towards IMS Core.

Dedicated and default bearers both will be lost with connection release.

Ok, so you mean bye is from network to UE and call will drop?

I mean dedicated bearer will be lost for QCI 1.

QCI 9 and QCI 5 bearer will remain only.

Network will send this bye but UE will not receive.

I don’t think default will be lost…

Please can give further clarification?

If RRC is drop all bearers are lost.

Only at new RRC setup default bearers will be established again in RRC reconfiguration.

You can check how many DRB are setup: 2 (qci9 and 5) or 3 (qci9, qci5 and qci1).

Let’s consider case without VoLTE.

In that case, if user inactivity will trigger, then network send RRC connection release to UE.

And UE move to RRC idle.

To come back to connected state, UE will use service req or TAU NAS procedure with bearer reconfigure only.

But no new default bearer message, i.e. activate default bearer setup there untill UE is detached or lost.

QCI9 and QCI5 are always activated even without VoLTE call setup.

After RRC is setup there is RRC reconfig to setup those 2 DRBs

Those are default bearers.

Not dedicated bearers like QCI1.


Activate default EPS bearer context not needed after RRC connection release, only reconfigure needed for QCI5, 9.

But for QCI1 activate dedicated bearer context needed.

I think UE wouldn’t get the chance to send any UL signalling.

Not sure if any lower layer signalling is performed before honoring the RRC connection release is honored.

I also have same opinion.

Network sending RRC Release means it removed the context at gNB.

So how the SIP message reaches?

LTE/NR & IMS have no connection except bearer or PDU session, LTE or NR just provides a bearer or PDU session, PCSCF is the entry point between LTE/NR & IMS .

In case of MO detach from UE side, UE will release RRC from its side, here its up to a intelligent UE to send bye before RRC release from UE side.

However a RRC release from network side, UE will have no knowledge as after RRC release from network side, network will release DRBs/NAS signaling explicitly which UE will not be aware, it all depends on media inactivity timer from IMS side, I haven’t checked UE side logs what UE sends in such situations, may be a a error code in UE side

There is no drop call
UE will send RRC Connection setup to same or different cell based on the outcome of cell selection. Upon successful rrc setup, both QCI5 and QCI1 e-RABs are setup in part of initial context setup as the EPS bearers are already activated