Wireless Joint

Modem: Quectel EM20-G (4G)
Router: WG3526 (now running WiFiX-NEXP1GO-GO2022-03-23a firmware)

Before Calyx terminated my Sprint plan and switched me to their T-Mobile plan, my setup was working just fine. Calyx just sent me the T-Mobile SIM and a 5G M2000 hotspot, and I first tested it out in the hotspot which worked as expected. I then took it out of the hotspot and put it in the EM20-G after removing the Sprint SIM. Initially, everything seemed to work, pretty much plug-and-play. All I had to change was the APN. I don't think I even had to change the TTL even though it was set to default.

But then I realized it was disconnecting pretty frequently, so I tried messing with the APN (r.ispsn, fast.t-mobile.com, B2B.tmobile.com, B2B.static), the TTL (default, 64, 65), 4G only vs. Automatic, QMI vs. MBIM mode, specifying the network (e.g. 310120), etc., and nothing seemed to help. While I was in the middle of troubleshooting the disconnects, it stopped connecting entirely, and it hasn't been able to connect since then. This happened just hours after unboxing the new SIM card and hotspot.

So before I can fix the issue with the frequent disconnects, I now have to fix the even bigger problem which is that the modem won't connect at all and I'm getting the following error any time it tries to connect.
Which is "SIM failure"?

This is what it shows in the system log when it tries to connect in QMI mode: and in MBIM mode: Additional info:
The SIM still works in the hotspot.

AT+COPS=? indicates the following networks are available: When it was able to connect, it seemed to be connected to 311490 on B41 (and B41 and B4 appear to be the only bands in range?)

In the time since it stopped connecting, I've upgraded the router firmware so that I could set PDP to IPv4 and set IPv6 to blank. I also tried every different combination of the configs mentioned above as well as the APN 'fbb.home'. No luck.

Any ideas?

Did you modify the modem to match the identity of the hotspot? It seems to be a requirement now.

I did try that (for the purpose of troubleshooting) and that resolved the issue. So it seems that T-Mobile has blacklisted my EM20-G's IMEI and in less than 24 hours of it being on the network.

FYI, for anyone's reference:
I tried calling T-Mobile Business to see if they could authorize the IMEI, but they said I'd have to talk to their Sprint team since it's classified as a Sprint plan for some reason (even though it's a new T-Mobile SIM from Calyx). Their Sprint team couldn't help me without providing the account PIN, so I stopped there.

If I were interested in further pursuing that solution, I would have called Calyx to see if they're aware that their plan / the SIMs that they're sending out are not plug-and-play with third-party modems, which was not the case pre T-Mobile, which I think was the appeal of Calyx to a lot of their customers.

If I could start over from scratch, I would have followed these steps: https://calyxinstitute.org/help/hotspot ... t-sim-card before putting the SIM in any device at all, and see if Calyx / Mobile Citizen could activate the SIM using my EM20-G's IMEI instead of the hotspot's. It would be interesting to see the result if someone tried that.

What's dumb is other than the Sprint based accounts, Tmobile hotspot SIMs DO swap between hotspot devices just fine. It's relatively new that this is happening on Tmobile hotspot SIMs.

Didneywhorl wrote: ↑Tue May 31, 2022 8:43 am Did you modify the modem to match the identity of the hotspot? It seems to be a requirement now.

Can you walk me through how to do that? Im having the same issue as the original poster.

I used the Sprint SIM card provided by Calyx for 18 months on our local one and only T-Mobile tower with good results. The connection was stable for literally months at a time. The tower connection was always shown as T-Mobile while data connection was shown as Sprint in GoldenOrb on a WE826-T2. Always had IPV4 and IPV6 addresses. We also took this setup on the road all over the western and northern tier states with excellent service (streaming NFL games on 32" TV) everywhere.

Now yesterday the dreaded new T-Mobile SIM card arrived in the mail. I followed the instructions for activating the SIM card by calling Mobile Citizen and giving the operator the IMEI of my Linkzone hot spot. I was tempted to give the operator the IMEI of my MC7411 modem that I actually use but decided not to tempt fate by going on the record violating their terms of service. The operator could not tell me any other settings that needed to be changed instead patching the call over to T-Mobile. The T-Mobile operator also couldn't tell me the correct settings for my hot spot insisting that I get the device on line and allow them to share my desktop so she could make the required changes. Naturally this didn't happen.

Knowing that the new T-Mobile SIM card was now locked to the IMEI of my Linkzone hot spot I followed the instructions from here:
https://wirelessjoint.com/viewtopic.php?t=696
To preform the IMEI magic on my MC7411. I had to remove the MC7411 from my router and use an USB sled to connect it to my desktop computer to do the magic. I put the modem back in the router and changed the APN to fast.t-mobile.com with no other changes to the router settings. On rebooting the router it connected to the tower with both IPV4 and IPV6 addresses. The connection was with T-Mobile for both the tower and data now. A speed test confirmed a good connection, 45Mbs down and the usual 3Mbs up. Then after about 10 minutes no data connection. The tower connection was still strong by the modem debug data. I rebooted the router and the connects were reestablished as expected. Again after a short period of time the data connection died. This went on for several hours every time I stopped by a computer and checked the connection (luckily my wife was out of the house for the day). Then I changed the APN in the router to b2b.tmobile.com as some others here have mentioned. A quick reboot of the router and the connections were reestablished again. This connection has been now working for 16 hours without a hiccup so I am keeping my fingers crossed.

I don't know about any streaming throttling because these days I bond the LTE router with Starlink for a faster connection. None of the streaming services we use allow the use of the bonded connection (their VPN restrictions) so we bypass to Starlink for streaming. OpenMPTCProuter seems to play nice using the b2b.tmobile.com APN in the LTE router but had many errors using fast.t-mobile.com APN. Another note is that I get totally different ranges of CGNATed IPV4 address depending on which APN and SIM card I use.

Edit. The change of SIM card also changed my POP from Seattle to Oakland for this device. I haven't checked if the APN matters yet (wife is home today so no messing with the network if it is up).

A quick update.

The b2b.tmobile.com APN was stable for 4 days with no drops or other funny stuff but still no testing for video throttling.

I decided to test for video throttling. Changed APN to fast.t-mobile.com, connection was IPV4V6. Connection was stable for a day. Tried changing to IPV4 only connection but this would not stick through a reboot or for more than 15 minutes, connection always reverted to IPV4V6. Video (Netflix) was throttled with both connections. Changed back to b2b.tmobile.com and set connection to IPV4, no video throttling. After about 15 min. connection reverted to IPV4V6 and video was throttled. A reboot came up as IPV4V6 connection with video throttling. I can't seem to force the modem to hold or reboot into an IPV4 connection. I am sure that I have disabled every place that IPV6 can be enabled under the Luci UI. I am running GoldenOrb_2021-05-31 ( OpenWrt 19.07.6 ) on the router right now.

islander261 wrote: ↑Tue Jun 07, 2022 9:24 am I am running GoldenOrb_2021-05-31 ( OpenWrt 19.07.6 ) on the router right now.

try a newer build? http://aturnofthenut.com/autobuilds/
there have been many bug fixes & improvements since the last 'official' release...