@Kevin_Z 

TL-MR3420 with Huawei E3372, 4G, Estonia

Periodic disconnection from 4G itself is not a big problem. Big problem is that after loosing 4G connection, it is never recovered. TL-MR3420 web interface shows, that 4G is disconnected and all buttons are inactive. E3372 led shows, that is has stable 4G connection. Only way to reconnect 4G is disconnecting/reconnecting 4G modem fom USB or power reset of TL-MR3420 modem. The situation is actually worse. In 10-20% of cases after power reset (or just  switching on the router) we have the same situation - modem shows stable 4G but is not connected to router. Restoring internet connection needs human intervention.

Our system is servicing devices, where humans are not  always present. So  I used a "workaround" as external resetting TL-MR3420 power every 6 hours. Well, sometimes the internet connection was not established after restart, but usually next restart was successful and I had internet just paused by 6 hours.  Anyway it was better than every time  drive over 100km to just reset modem.

Finally I found device named  "Keep Connect Router Rebooter", which does what needed: it is monitoring over WiFi internet connection and when it is lost, does power reset of router (3 attempts, configurable). If there is still no connection, it repeats these attempts every  4 hours (configurable) until connection is restored.

So, for me the problem seems to be solved (externally), but I have a proposal. Algorithm, described above (OK, in fact it is a bit more complicated), could be be realized on the router level. That means, why not to add option: "Hold/restore 4G connection", where in case of loosing 4G connection, USB connection with 4G modem is restarted 2-3 times, and if no success, repeated every 3-4 hours. Or, instead of just restart USB, reset whole modem, which will restart everything.

Right now, if 4G is once lost, there are no attempts at all to recover this connection.

  @valentin_a 

Exactly this! I just ordered Shelly Plug Plus S that I will script to hard boot the tp-link modem when the connection is lost. 

It is unbelievable that these devices can't reconnect when the connection is lost. This should be very basic operation for a modem. The modem knows that the connection is lost but it still can't reconnect and nightly boots do not usually help. I have to unplug the modem to get it online again. I have NX510v 5g modem that is using 4g+5g, so things do not get better with tp-link 5g modems either.

  @Sunshine 

Hi! Right now I am away from the router but in couple of days I will be able to give more precise answer.

I have MR3420 v5. Firmware I do not remember, but latest available by september 2023.

I have tried this MR3420 with three diferent USB modems: plain E3372 with software of our ISP Elisa, E3372h-320 (it is connected right now) and E3372-325 (without h in name).

E3372 is oldest and works without problems with three different MR3420 v5 I have with original (not updated) firmware.

E3372h-320 initially did not want to connect to 4G (only 3G worked), but after MR3420 firmware upgrade (somewhere in june 2023) started working.

E3372-325 did not connect to 4G even with upgraded (in june 2023) MR3420 firmware. Did not check yet with latest one but try to do it soon.

Also small addition to my previous post. The modem connects to the relatively weak 4G quite a long time. Therefore when network type was set to "Automatic", then during startup in 50% of cases MR3420 gives up (shows USB disconnected) earlyer than modem was able to establish connection to G4. When I changed network type to G4, it improved situation - success in 85% and failure in 15% of cases. In case of failure helps only manual reconnect of USB or restart of router. 

  @walzu 

Good luck with programming!

Agree, that periodic checking of internet connection and if necessary, resetting/reinitializing USB connection to the modem should be not too difficult. But from the other hand, external rebooter has one advantage, which is a bit harder to implement on the router side. Because this rebooter is connecting to the router over WiFi, it checks also if WiFi is working and restarts router when WiFi is lost. Checking WiFi from the router side is not so easy. OK, presence of connected WiFi devices can be monitored on the router side, but there can be devices that connect to WiFi just periodically. As example, Shelly H&T, which connects to WiFi every 10 minutes, reports humidity an temperature and disconnects. If there are only such devices, most of time there will be silence in Wifi and no connected devices. In this case, to avoid unnecessary reboots, there should be then configured some longer delay "without dvices" to wait, if some WiFi device will appear. Or some "anchor" device, which is constantly connected to the router, showing, that WiFi is OK.  

It's crazy that this is still an issue. It is almost exactly 12 months since I got an Huawei B818-263 4G router, and it has been almost flawless throughout that time. I use a TP-Link Mesh, and have had very brief connection drops. I think I've reset the router twice, perhaps three times, along with the entire mesh. The TP-Link router is an expensive ornament in my 'box of bits'.

  @valentin_a 

Thanks!

Actually the wifi has never been a problem on my system. I'm currently using Ubiquiti router, switches + AP's and these have been really reliable. My TP-Link Modem is only acting as a modem, so it should not have too much to do. This connection is used to monitor and control our second home heating (150km away) so it is quite crucial. I have to figure out something to make the connection last. Now it is dropping the connections almost everyday. After power cycle I get really nice 160Mbps connection, but I'm not interested in driving there everyday :D

Winter is coming!! Greetings from Finland :)

  @walzu 

Exactly my case, only the distance is shorter - 100 km  Initially I used Huawei e5576-32 mobile WiFi. It has battery inside, so it survives power breaks and lost G4 only a couple of times during last winter. Unfortunately in this case only hard reset with reboot restored connection. Also it has quite weak WiFi signal which caused WiFi connection problems with Shelly thermometers. Therefore this summer I replaced this one by MR3420 with E3372. No WifFi problems at all, but once during a month or two it is loosing G4. Winter in Estonia is almost the same as in South-Finland :) so I had to prepare something, that will restore lost G4 connection without my intervence. And I hope that right now I have solution. Wiil see :)

  @Sunshine 

Hi! Finally I can send you exact versions of hardware and firmware.

Router:

Firmware Version:          1.8.0 0.9.1 v0001.0 Build 211220 Rel.70276n

Hardware Version:         TL-MR3420 v5 00000002

G3/G4 modem:

Device name                     E3372h-320

Hardware version           CL4E3372HM

Software version            11.0.1.1(H697SP1C983)

Web UI version                               WEBUI 11.0.1.1(W13SP1C7110)