DUT not sending PDN request for IMS and SIP Registration Request

Hello Experts,
Please suggest on below questions:

Question 1:
DUT & Network is supporting VoLTE but still DUT is NOT sending PDN request for IMS.
How can we verify that issue in logs? What can be the causes?

Question 2:
DUT QCI-5 Established done, but DUT NOT sending SIP Registration Request.
How can we verify that issue in logs? What can be the causes?

*DUT = Device Under Test

Check Attach Accept if IMS VoPS is 1 or not.
Then check UE should have IMS profile for this network, in case not, some UE avoid sending IMS PDN request.
If SIP registration is not sent, then check pcscf address is valid or check wireshark logs for any other issue.

This is not required for IMS bearer setup or SIP registration.
The VoPS is only to specify if voice calls over PS are supported but does not prevent UE from registering to IMS for other applications such as SMS and RCS.

This is exactly right. But how to make a device (off the shelf) get IMS profile for a test network in lab?
I know iPhone now can be switched on for VoLTE but what to do for Android devices if there’s no carrier settings for the particular PLMN?

To add to that, VoPS can be specified per tracking area so you can still have IMS registration across the network but if UE happens to cross TAC boundary into the non VoPS area it will do csfb for MO call! and TAS on MT call will determine during Terminating Access Domain Selection (T-ADS) if the UE is in a VoPS area by querying the MME via HSS.

Hope so provisioning for VoLTE profile there in HSS as for registration P-CSCF contact I-CSCFf then S-CSCF contact HSS for authentication for VoLTE user.

Agreed, but ideally doesn’t make sense to have IMS Registration if we don’t have Voice available (except for US carriers who have SMS over IMS).

I am just responding to what can be issue, you can update the android profiles but would require separate effort for that.

Network can even tear down the IMS EPS bearer in TAU Accept, but how is that related to the query here?

Sure but as I mention, it’s possible the operator doesn’t have good quality in certain area and will set the VoPS as false until it can be optimized. In those scenarios the UE will still register for IMS even if it can’t make a voice call at that point.

Just stating the VoPS does not prevent IMS bearer to be established. Also does not have any impact on the IMS registration.
Voice and IMS are two separate things and I’m trying to make sure there is not misinformation here.

Yeah that seems to be the only way, but can this be done for non-rooted android phone? Or can only be updated when you have root?

Interesting take on things.
Please share a few instances where operator doesn’t have Voice over IMS but IMS bearer is set up or SIP Registration is used in phones.

Mostly rooted.
Ideally this shouldn’t be the case with live networks, maybe lab networks.

Yes for sure, to use SMS and RCS service they do not require Voice-over-PS flag to be set.

My bad. The part where query is about NW/Device supporting IMS and QCI 5 is already setup.
Then looks more like device limitation of mot being able to send Registration.
Maybe a previous backoff or retry after or else not supporting ip type. Need to check the wireshark logs for this :+1:t2:.

Agreed, just want to know if there are operators actually using IMS bearer only for RCS and SMS.

Yeah for 2nd query I think you’re right the PCSCF is possibly not set, it can also be tricky when you are capturing for SIP and don’t see the REGISTER message because it’s possible there was no TCP handshake established and (possibly) your wireshark filter is not set right to see the multiple TCP SYN with no reply.

Agreed :+1:t2:.

I don’t know of specific example where an operator would invest in setting up IMS if not to support VoLTE - but i have seen it where the whole network is not “production ready” to deliver VoLTE but that doesn’t stop phone from registering for IMS to use those other services such as SMS and RCS (honestly I can’t think of any others except the ‘presence’ service and video calling…are there any other applications that use IMS?)