VoLTE and VoNR issue

[Addhiya]

Hello Mr. Herlesupreeth, thank you in advance for the documentation you have created. I would like to ask about VoLTE and VoNR.

I tested using three different device brands: Samsung, Xiaomi, and Oppo. I also tested on two types of servers: Kamailio and OpenSIPS.

On Kamailio (4G), all devices work properly with VoLTE—they are able to perform calls, video calls, and SMS without issues.

However, on OpenSIPS, only the Samsung device successfully performs a SUBSCRIBE. In sngrep, it can be observed that it first receives a REGISTER, and then performs a SUBSCRIBE once IMS is successful. Meanwhile, Oppo and Xiaomi devices do not perform a SUBSCRIBE; they only REGISTER and receive a 401 Unauthorized response. Despite this, they still display the VoLTE icon and can make calls and send SMS, but they are unable to perform video calls.

In the 5G scenario, Kamailio behaves the same as in 4G. OpenSIPS also shows similar behavior as in 4G. However, the difference is that even though Oppo and Xiaomi devices display the VoLTE icon, they are unable to perform calls, video calls, or send SMS.

Is there any solution or insight regarding this issue?

Thank you.

[herlesupreeth]

1. OpenSIPs does not support video calling
2. IMS support in OpenSIPs is quite basic at the moment
3. In 5G scenario, I personally havent tested using OpenSIPs (it was a contribution from a community member) so it would be broken

[Addhiya]

Thank you for your response. However, I would like to ask further regarding the first point: if OpenSIPs does not support video calling, why is it that when I use a Samsung device, the video calling feature works? The same behavior also occurs on 5G.

Thank you.

[herlesupreeth]

why is it that when I use a Samsung device, the video calling feature works? The same behavior also occurs on 5G.

that's because Samsung device may have been configured to not require QoS for video flow and still let call go through (I remember seeing such an config in Samsung IMS settings app).

[Addhiya]

Oh, alrightt thank you, I really appreciate your explanation.

I have one final question. In the gnb.yml file, the default configuration is dl_arfcn: 632628 on band n78. However, this frequency and band can only be detected by Samsung and Oppo devices, while Xiaomi devices cannot detect any signal when using this configuration.

Do you have any recommendations for band and ARFCN values that would work on Xiaomi?

Thank you.

[herlesupreeth]

@Addhiya I use dl_arfcn: 650000 for all my testing

[Addhiya]

Thank you for your suggestion. However, after trying ARFCN on bands n77 and n78, Xiaomi devices still cannot detect any signal, and no logs appear on the core. I have also tried bands n40 and n41, but there is still no signal detected (although I have not tested the entire ARFCN range yet).

Do you have any other suggestions that might help resolve this issue? Thank you.

Xiaomi device : Poco X5 Pro 5G

[herlesupreeth]

Aah i remember now. For Xiaomi device there is a secret code you need to dial once which enables 5G SA and provides you option to toggle in settings

Activate hidden SA option by dialing *#*#726633#*#*

[Addhiya]

Thank you for your suggestion. After trying it, the issue is still not resolved. The S-CSCF only performs debugging for IMSI registration, but the UE does not send any response. I suspect that the problem may still be related to the frequency being used.

However, I would like to ask: when using Kamailio, is it normal that RTCP packets are not captured in Wireshark on 4G? If so, is there any solution to this issue? On 5G, RTCP packets can be captured in Wireshark, whereas on 4G there are no RTCP packets observed at all.

Thank you.

[herlesupreeth]

However, I would like to ask: when using Kamailio, is it normal that RTCP packets are not captured in Wireshark on 4G?

no, usually you see RTCP packets at certain intervals