Carrier aggregation (CA) troubles, most likely not related to this module but related how the OS interacts with the modem/firmware

[zearp]

First off, I'm pretty sure this is not related to the module but to firmware and/or how the OS interacts with it as its work fine on Windows in both modes. This seems related to Linux. I haven't tried any of the bsd's. I don't know where else to go as this seems to be the place with a lot of knowledge and development. Sorry if this isn't the right place.

I'm not a programmer myself and just an enthusiast who wants to get the modem to work to the best of its abilities. I can do testing/debugging and report my findings. I have a few of these modems, both in usb and pci mode.

The issue I been having is that CA stops working after a while, I do not know why. There is not indication of anything happening relating to this in logs or dmesg. Most likely lack of relevant log/debug options. I can run at+xlec and see it works and then after a while it stops working and doesn't fix itself until I reboot or re-plug when using usb. Without CA I get about 100mbit/s which while still very usable is slower than the over 300mb/s I get when it's working.

This happens both in pci and usb mode, it also seems to happen on OpenWrt and my Zyxel router which I believe also runs an OpenWrt based firmware. I've also tried it in usb mode on some other routers and pc's all with the same results unless it's Windows. It only seems to last in Windows, even when leaving the laptop on overnight the next morning the speeds are still as expected.

It usually happens within a few hours but it can take a while, rebooting the machine or re-plugging the modem seems to fix it, until it happens again. I wish I could find a way to reproduce it properly.

I tried some different firmware version as explained on this site, the comments once translated show some other people have similar issues on Linux but no solutions. I do not know how to properly troubleshoot this or even how to reproduce it reliably without waiting for until it happens. I tried putting some load on the connection but that doesn't seem to trigger it.

I don't know if this is fixable at all since from my understanding CA is done at firmware level and we can't influence it beyond maybe locking to certain bands. Which I have also tried. Used a public antenna map which has all the info needed on which bands we have here. I live within the line of sigh of 2 cell towers in the centre of town. Signal strength isn't really an issue. Locking it to the available bands or allowing it to use all bands also did not make a difference.

I hope there are other ways to fix this than firmware as Intel will likely never make a new firmware for this modem again, or fix any outstanding bugs that may cause this to happen in certain environments.

I'm opening this issue mainly as this seems to a place with a lot of knowledge and development for this modem. I would open a bug a ModemManager as since a very recent merge it all works out of the box now too. Just have to compile ModemManager from source and I was online in under a minute, same thing happens there. I wish I could reproduce this properly.

I hope maybe we can figure it out together as I seen others run into the same issue and some might run into it without realising the connection slowing down is due to CA not working properly.

Sorry for the long rambling issue, please close/delete if it's unwanted.