We had recently deployed a few Cellular IoT devices on the field, using SIMs from a certain provider (Airtel India). They had provided us with an APN, but we chose not to program our device with the APN, as it was working even without it. Further, we had earlier noticed that setting the APN didn't make any difference for all the cellular providers we tested here in India (in fact, APN of one provider would work for another also, without issues).
However, some of our devices deployed in a certain location stopped working recently. The issue was that we had not set the APN. However, devices deployed in other locations continued to work. The network connectivity was proper in all the locations and mobile phones were working.
Now, here are a few things that bewilder me about APN:
- How does it happen that APN of one provider work for the other?
- How does it happen that devices in one location stop working and in the other location continue to work, all of them NOT programmed with APN setting?
- How exactly does changing the APN affect the connectivity?
I have read many articles on the Internet and questions on other forums to understand the mechanism of how APNs work, however the understanding on how it explains the behavior we are encountering, still eludes me.