B524 does not connect to the best cellular network


Yesterday I got my first B524 with the EtherSIM technology. Today I have time to test the module for the first time. The installation was easy as always - the B524 connects to the Cell Operator H3G by using LTE, the signal quality was 58% - everything works great.

Austria | 3 (Drei) => this in fact H3G - 58%
Austria | A1
Austria | T-Mobile

5 Minutes before I used an B523 on the same spot off my table and this one only connects to the Cell Operator A1 (H3G and T-Mobile are not supported) and with 90% of signal quality!

B524 should connect to the best Network, but it does not. I could not find any information regarding this observation.

  • How does the network selection really work?
  • Can I influence this behavior?

Thanks in advance for any help

The choice of operator is made by a combination of the SIM card and the cellular modem, and the manufacturers do not document exactly how it works. It’s more complicated than “best” because the SIM provider may impose a preference.

Unfortunately there’s no good way to configure the preference list.

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Hi rickkas7!

Thanks so much for this information. Next week we start some tests and it’s important for me to know the details…

Have a nice Weekend

We have a situation where several B524 based products have gone offline simultaneously for hours blinking no internet, while B523 stay online.

The carrier the B524 chose, has reported updating the network with effect on SMS voice and data.

Connection handling is left to the OS and B524 has access to more carriers, and restarting the modules does not help either.

So I guess the modem/sim choose the carrier, and the OS reports no internet without further action?

Have anyone tried a fix for this, taking control with the connection handling to force other carriers?

The only thing I can think of, is cycling the modem between LTE, 2G or 3G specifically until connected, but it would be difficult to keep record and clean up.

The EtherSIM service provider caused this, so a a local carrier switch would likely be unhelpful. Device offline logs stated exactly the same timestamps for going offline and online again without self inflicted restarts or resets.

This is a product with a gateway logging and regularly uploading data from local wireless sensors, to a web service. The excellent library PublishQueuePosixRK by @rickkas7 made sure devices that were left running, continued to pick up data and uploaded these, when the connection was restored. Highly recommended :+1:

One caveat is devices being power cycled will not come online again during the outage to learn time and date, and is no longer able to timestamp measurements for later upload to a server.

So in this setup, an intervention pulling the plug on the device with a watchdog, if enough uploads fails, should be used sparingly, if continued operation with collecting data for later upload is a priority.

During investigating this, I found a source on PLMN selection (how a network is selected) that might be interesting others:

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