We get several calls each week from customers that have purchased SIM cards and have been told that the SIM will automatically connect to the fastest network and will work on all networks.
We are not going to answer here about how they do that – you will need to ask them to explain it – but here is a bit of common sense to bear in mind when using the SIM in a 3G or 4G Router.
Supposing you inserted this multi network SIM card into a router that has a single 3G/4G modem to provide a single connection and turn the router on and configure the APN (we are assuming that your SIM has a specific APN to use)
The router may be installed in a location with access to 5, 10 or possibly 20 mobile cell sites.
Here is the common sense bit:-
In order to check the signal strength and download and upload speeds the router would need to connect to all the different base stations and check the strength and download speed (signal strength does not always indicate the best service or speeds because this could depend upon the number of users using the 3G/4g service). The SIM card would somehow need to command the router to connect to all the cell sites, make the signal and speed tests and store the data, disconnect and then connect to the next cell site until it has connected to all the available cell sites and performed the relevant tests. The SIM would then have to analyse the data which it has somehow managed to make the router store and then command the router to connect to the best service. For 20 cell sites this would take around an hour before you have a permanent connection.
However that data was only pertinent to the time of first switching on the router – the SIM would have to regularly scan the networks in order to fulfill the promise of ‘using the fastest mobile service available’ and of course every time the router was restarted we assume that the SIM would have to perform all these tests.
This is what we guess is the underlying promise made my the mobile providers offering the multi-network M2M SIM cards, however – we don’t sell any routers that will allow the SIM card to connect to all the available networks, perform speeds tests, store speed test data or feed back any data to the mobile network. In reality the router connects to the first available network and if you power it off and on it just connects back to the same network – so if it connects to O2 when first used then the next time it connects it will use O2 as the preferred network.
So – that is the common sense way of thinking about what would be involved in getting your SIM card to actually work on the fastest available network – and you would need to contact your SIM provider to get them to explain how it checks all the sites in the router location for both signal strength and download and upload speeds.