The call occasionally fails to connect

[Sandhyalekha-4]

Hi All,

The call occasionally fails to connect. It will reconnect after 15 minutes. I have attached the logs

Calls_failure_issue.zip

Test procedure:
One pair of volte call testing continuously. Sometimes the call dropped within 1 hour, and it would not reconnect immediately.

[herlesupreeth]

@Sandhyalekha-4 I am missing the context here. I see the UE refreshing its registration but I dont see any SIP INVITE from either of the UEs so I am not sure which fail you are referring here

[Sandhyalekha-4]

Hi Supreeth, could you please review this image? I've highlighted the INVITE packet. I'm trying to understand why the 183 Session Progress message isn't received after the INVITE. Also, can you check the pcap log from where the last SIP message, 'Modify Bearer Response'? The SIP flow shows: INVITE → 100 Trying → 408 Request Timeout → 500 Server Internal Error on LIR, followed by selection of the next S-CSCF."

But after 15 minutes, the call works properly. What could be the reason for the connection occurring after 15 minutes?

[herlesupreeth]

I've highlighted the INVITE packet. I'm trying to understand why the 183 Session Progress message isn't received after the INVITE.

I am guessing here, looks like the SIP INVITE was not being forwarded to the called UE. Is the called UE registered with IMS?

But after 15 minutes, the call works properly. What could be the reason for the connection occurring after 15 minutes?

It could be that UE registered correctly with IMS and call went through.

[Sandhyalekha-4]

UE registration is not successful, it's been waiting for 3 seconds, but ue is not registered. First and second attempts at UE registration are successful, but why is it taking more time to register for the third attempt? Is there a timer to check this?

[herlesupreeth]

@Sandhyalekha-4 Please pull the latest changes in master branch and give it a try. It has some fixes for session refresh.

[Sandhyalekha-4]

Okay sure, Thank you Supreeth. I will try it and get back to you

[Sandhyalekha-4]

https://drive.google.com/file/d/1tEbeRk9xxip2nLc9p3rfhBwGmKj7C78n/view?usp=drive_link

I tested for 2 and half hour. The call didn't disconnect, so I disconnected the call and tried a few more subsequent VILTE calls for 2-3 mins and it worked without any issue. Later, I changed the subscription to 10 mins in pcscf,scscf and icscf .. The call disconnected in 10 minutes with QOS fail and subsequent calls are also not working. When I checked the loopback log, a BYE SIP message saying QOS failed, the bearer is not getting deleted.

[herlesupreeth]

Later, I changed the subscription to 10 mins in pcscf,scscf and icscf .

Please dont do this because the UE registering to the IMS is using an expire much higher than that.

Expires: 600000

[Sandhyalekha-4]

Okay, Supreeth, is it possible to reduce the timer expiry?
Expires: 600000

[herlesupreeth]

This is a value sent by UE. Unless you have a phone with Engineer Mode enabled for IMS you cant change that value

[Sandhyalekha-4]

Hi Supreeth, Thanks for your quick response. I had got an ue that expires for 4 hours and we had kept the subscription time as 5 hrs. But once the call reaches 5 hrs again, QOS fails, and subsequent calls are not working. (PLMN is 40410 and UE expiry time is 14400). Please check the attached logs.

https://drive.google.com/drive/folders/1ZjZqIyIgPDvOMP0RX9R7_335r8C162n4?usp=sharing

[herlesupreeth]

hmm, this is exactly what I feared when I set the subscription expires to that value. Thanks for sharing the logs. I will take a look if I can find a solution to this or not. In the worst case I can reject the session refresh from UE and force UE to initiate a fresh register.

[Sandhyalekha-4]

Below is another observation:
I have tested with subscription times of 5 minutes and 10 minutes. For 5 minutes, Vilte calls are connected twice, but for the 10-minute timer, Vilte is not connected for 2nd attempt.
Compared both logs, deleted the bearer session and create bearer session SIP messages are not there for the subscription time of 10 minutes compared to 5mins timer. Attached the loopback logs.
https://drive.google.com/drive/folders/1aihLbEhAcpzPKqeYh4ZDou1YaqVop-ZP?usp=sharing

[herlesupreeth]

I finally managed to fix the session refresh issue. Please pull latest changes and give a try. I tested it locally by placing a call after subscription time expires and session refreshes.

[Sandhyalekha-4]

https://drive.google.com/drive/folders/1RN1rpbOrKktryKKHuaDCDoBymTy-mtC8?usp=sharing
Hi Supreeth, thanks for the update. I tested with a 10‑minute subscription expiry and noticed that session refreshes are taking some time. It worked successfully twice, but on the third attempt, the VILTE call ended after 2 minutes. When I tried to redial, the video appeared blurred.

I tested with a 5‑hour subscription expiry, and on the second attempt to redial, the call did not connect (the UE displayed “calling” but the call was not received). Attached the loopback logs.