Hello:
I’m using Hologram SIM card with a SIM800 modem controlled from an embedded system (no OS), using AT commands.
I used the GSM modem to connect to AWS with MQTT and SSL. So far I can establish a connection and send/receive data, but I see connection is not very reliable, so I get lots of socket errors which disconnect MQTT session.
I can see from the Dashboard that the SIM is using T-Mobile in 2G mode. I’m wondering if this is an issue… I see people here talking about using 3G and 4G, and other providers such as AT&T as well… How can I switch to these 3G or 4G connectivity? Are there specific AT commands for this? I would like to try other modes to see if I can get a more reliable connectivity.
Sim800 only works on 2G, you would have to buy a 3G or 4G capable module to use those networks. 4G LTE networks are more reliable as they are newer and common technology (where 2g is obsolete) and they have support for more carriers (Verizon, AT&T and T-Mobile in USA).
Only T-Mobile supports 2G in the USA so there are no alternatives if you have poor T-Mobile signal or are not happy with the network.
I suggest looking at the Nova or Sara R410M based devices to prototype. These modules are more expensive but provide access to 4G networks and better connectivity. 4G is also “always online” unlike 2G where you need to register and de-regester from GPRS. You allways have an IP with LTE.
Note regardless of technology cellular is less reliable than hardwired or even wifi so building in tolerance for recovering a closed connectin will be important. All cell provides will also shutdown connections after a certain period of no activity so you may need to continually send heartbeats to keep the link up.