Xperia 1 II loses 4G connection in Telenor Bulgaria's network

[peter_sl]

Hello,

I've been using Xperia 1 II (XQ-AT51) for about 3 months and I keep experiencing severe network issues with Bulgaria's Telenor mobile network operator. When I'm outside of urban areas, the handset shows it is connected to 4G, but when I try to use data it immediately disconnects and displays "No coverage" for a few seconds. Afterwards, it reconnects, but it only lasts until I attempt to use data again. This cycle continues infinitely, regardless of whether I'm moving or staying still. The preferred networks setting is set to 4G/3G/2G and if I change it to 3G/2G, I don't experience the problem. Other phones in the same area don't have any network issues. You can watch a screen recording of the handset's behaviour here.

And here comes the curious part: when I go to Software Info in the Service Menu (*#*#7378423#*#* > Service Info > Software Info) I see that the Current Modem Config is Telenor_Sweden.

This is totally incorrect in my opinion and probably has much to do with the network problems of the phone, because Telenor Bulgaria does not use the same set of 4G frequency bands as Telenor Sweden, which renders the handset unable to find the frequencies it expects. If I put a SIM card of another Bulgarian operator (A1, Bulsatcom) into the phone, the Current Modem Config changes to ROW_Commercial.

I'm reluctant to take this to a service center, because as I mentioned above, this happens only outside of urban areas, and will not be reproducible at all in the city where the service center is. I'd like to hear some opinions about my theory that the wrong modem configuration is causing the network issues, as well as how you think this can be corrected. I'm guessing it would need Sony to fix the software wrongly identifying Telenor Bulgaria's SIM card as Telenor Sweden one.

Thank you,

Petar

[CosmicTomato]

Have you given other troubleshooting steps a try? like the software repair or factory reset, it's odd to be configured to Sweden, could be a software bug.

[peter_sl]

I have tried resetting and repairing, it does not help. And as I mentioned, this problem persists on a second brand new device, that I got after I gave my first one for repair. I am pretty confident that the carrier policy XML file is messed up. It is basically a list of rules that try to match the carrier name and apply different settings to the modem, turning features on and off. I imagine that there is a rule saying that if the carrier name is Telenor, then apply modem configuration for Telenor Sweden, which is not quite right for Telenor BG. It is explained here. Unfortunately regular users have no access to this XML file, unless they root their phone, which is something I don't want to do just yet. I don't know if this carrier policy comes from Qualcomm or from Sony, but in either case it's them who have to figure it out and fix it. Fortunately, I was able to get in touch today with Mr. Malchev, Sony Mobile Bulgaria's National Account Manager, and he was kind enough to take this and try to escalate it to a responsible person, so I'm a bit positive that it may be solved with a future software update.

[Strampke]

OK, there you have a point.

Last year I was in Germany and put my Dutch Vodaphone in my device after a reset.

It picked the settings automatic and there was no mobile internet.

Once I applied the settings from the Dutch providers' website it worked.

Never checked if there was a difference or what, but it restored mobile internet, that's for shure.

[peter_sl]

I understand what you did, but it seems we are talking about different things here. I think you received automatic Access Point Names, which are high level settings, that control what host, port, username and password your device uses to connect to the internet in the current provider's network. Modem configuration, on the other hand is low level hardware settings, that control what LTE and 5G frequency bands are used, carrier aggregation, VoLTE support and probably lots of other stuff that tells the phone modem how to connect to the provider network. APNs are user-configurable and can be provisioned by the mobile provider, while modem configurations are baked into the firmware and can be changed only by the manufacturer and controlled by carrier policies.

If I root my phone, I will probably follow these instructions https://mt-tech.fi/en/modify-sony-xperia-1-ii-lte-a-and-5g-nr-combinations/, but I'd rather wait a bit more to see if this problem will be resolved the proper way.

[Poseng1]

I bought mine in Hong Kong and used it in South Africa. I also have a problem with one of my network provider. Exactly the same problem with the 4g data, the signal bar just went blank and reconnects. 

I tried with another service provider, there is no problem. I thought it was the service provider problem and told them to fix their tower or reset my sim card. It still didn't went well. I also change to a new sim card to try, same problem. 3g works perfectly well.

This guy from this website also had the same problem  https://www.reddit.com/r/SonyXperia/comments/hvtkil/network_issues_on_xperia_1_ii/  , but he said he got his problem fixed from the update that was 2 months ago, but also updated to that version, even the one in November. But my 4g problem is still there, so I hope Sony gets this fixed. 

[peter_sl]

I'm only speculating at this point, but it seems that the transition to 5G has required some major changes to the carrier policies and modem configurations and not everything works perfectly yet. Seeing that Reddit guy's problem get solved by a firmware update makes me think that Sony can fix these issues individually for each provider, so we have to let them know when we have them. So Poseng1, I guess it would be helpful if you share what your provider and current modem config are when you have the problem, and if the modem config changes when you switch providers.

[CosmicTomato]

I agree with Peter, if this is a specific issue, they may not know of it, you need to have yourself be heard, test yourself the configuration of a different network SIM on the phone, then contact Support with the results asking it to be raised for resolution.

[Poseng1]

Well I did share it with them. But they just say they will investigate. So I'm really not sure if the carrier will get it solved.

I wonder if it's really the 5g modem is the problem. Does the Samsung or Huawei with 5G modem also has this problem? Too bad I don't have anyone I know that has a 5g phone to test

[peter_sl]

My experience with Sony's Bulgarian support is that they have a list of prepared problems and answers and are not able to do anything outside of it.

I was able to extract the phone logs by connecting it to a computer and running adb logcat. Here are some lines at the time the phone loses network and they definitely mention the modem:

09-14 20:19:09.765 1441 1441 I QTI_SDM_INFO: [qti_rmnet_modem.c:1287] qti_rmnet_modem_recv_msg():Read -1 data from modem device file
09-14 20:19:09.765 1441 1441 E QTI_SDM_INFO: [qti_rmnet_modem.c:1292] qti_rmnet_modem_recv_msg():Failed to read from the dev file. Errno 512 error msg=Unknown error 512

The full log is here: https://app.box.com/s/mrtoga1wsngojt2kc436c4x109x9q9m1 

I believe these network issues are observed only with the Snapdragon X55 modem, so it would be interesting to compare with other devices that have it, which are all devices running on Snapdragon 865. Here is a list of them: https://en.wikichip.org/wiki/qualcomm/snapdragon_800/865#Utilizing_devices. Only the North American Samsung phones are on the list and there are no Huawei phones at all.

[Poseng1]

I wonder if we can make a complaint to qualcomm, maybe they can update their drivers. Or maybe they aren't even aware of it