VoWiFi: Why the ePDG is designed to be behind the PGW?

True, but one query how ciphering is happening in Vo-WiFi?
One curious query being radio guy…

How ciphering is being done in Vo-WiFi case? If it is not than is it legal?

Yes, irrespective it finally all depends on operator requirements.

I would like to comment on this with my experience in Jio network.

In this Vo-WiFi also works fine even there is no LTE connection.
When data is disabled, n UE connected to WiFi of Jio hotspots (mall, park, etc) that time, it’s “Jio Private net”.
On this the authentication is through SIM and hence data is reducing from daily balance of SIM itself.
When connected to any other WiFi, device only is using Network n sim is not playing any role n hence no VoWiFi.

This is what I have seen.
Please correct me if am wrong.

Yes @needoos.th, correct.

If WiFi calling is on, then VoWiFi registration should happen through AAA.

Yes @chitrangankumar, agreed. That is the actual need of VoWiFi too.

Ciphering should be done.
I will dig into the specs and will come back.

It is IKE+ESP protocol suite for encryption all traffic from UE till ePDG.

Thanks @needoos.th ji, does the encryption is again performed using the Ck generated by the HSS in the S6b ULA?

Partially correct. Device uses WiFi for internet, while SIM is used to authenticate the subscriber with the operator.

Thanks @RMatolia for the information, but which node will stop subscriber from latching to WiFi if he is not latched with LTE?

Are you able to do the VoWiFi registration when you put device in 2G only and restart the device?
Ideally it should happen.

I didn’t restart, but I disabled data, kept the phone in 2G and was able to do a WiFi call.

Ok, try restarting or APM (Airplane Mode) ON/OFF.
Let’s see then… keep the WiFi ON.

I did this case. Same result.
Able to do WiFi call, with WiFi call enabled, data disabled, 2G enabled, VoLTE disabled.


Yes :point_up:t3:… it’s correct behaviour, this is the purpose of VoWiFi.

Now coming to your query PDN Gateway is for IP assignment, bearer enforcement and VoLTE/VoWifi HO.

You need connection of ePDG with EPC, right? Directly can’t go to IMS.

The WiFi calling symbol is visible, though really not sure whether the call is going over WiFi or CS…

It should mean that VoWifi registration is Successful.

I said this, as the device will work in the same way if the sin is removed also.

My phone shows WiFi when it has gone through VoWiFi.

I get this when enabling vowifi on the phone. Why is google being sent location info for enabling VoWiFi.
Is there a colab between Google and Airtel in India?


PDN Gateway is for:

  1. IP assignment - :white_check_mark:
  2. bearer enforcement - :white_check_mark:
  3. VoLTE/VoWifi HO - :white_check_mark:

Thanks @jsdeoraj, will go in depth of these things.

Sure dear.
It was really interesting question.
Please let us know when you come up with more insights.

LTE bearer always ON, can’t disable data at all, hence min sig still flows on LTE for ch service selection.

Yes, when you turn OFF Mobile Data feature in UE it is the DRB flow that is stopped, not SRB.