NB-IoT and SMS
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I've been trying to make a SIMCom SIM7020G send an SMS.
We're adding remote monitoring via GSM/LTE to one of our (physical device) products. And so I got an updated PCB, with a modem module soldered on, plopped on my desk. And a "SIM7020 Series_AT Command Manual" (sic.).
The manual details AT commands for sending and reading SMS messages. But when I try to send one, I get:
+CMS ERROR: protocol error, unspecifiedThere's a service center defined, or at least the modem claims as much:
+CSCA: "+358447983500",145Since testing with the modem module soldered on is a bit difficult (there's no good port for passthrough functionality on our device), I asked if I could get one of the modems not-soldered-in as a standalone thingy. And it turns out that was as easy request. I got one of these:
With a mark on the "NB-IoT" box. So I went looking for whether NB-IoT is an obstacle to SMS. And... it probably is; I found pages that either imply or outright state as much.
However, I also got told a hearsay about the protocol itself supporting SMS, but not mandating its implementation by mobile operators over NB-IoT. So a lot of operators just don't support it. Which would go a long way toward explaining why the SIM7020 AT manual lists the SMS commands, and the modem itself responding to them in a sane fashion, apart from the errors.
So, uh... anyone here able to settle that question for me conclusively?
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From some cursory Googling, it appears that NB-IoT itself, as specced, does not have support for SMS but that it might somehow coexist with LTE-M which does.
Edit: And according to this page, which seems to detail a bit more about it, NB-IoT's upload rate is about 20Kbps
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@e4tmyl33t I guess that's it, then. Time to order the LTE version, and hope the module inside is pin-compatible. Because if it's not, then our first delivery is going to be either very late or built on wire spaghetti.
