Previously I have developed a solution using SIM5300E with connection to Azure MQTT servers over TCP. For this I used the command “AT+CIPSSL=1”. This works perfectly to Azure over SSL, so the certificate on the SIM530E module must be valid for Azure.
Now I am designing a new version using SIM868.
With the SIM868 I want to connect to Azure over TCP. Using the same AT commands I find that the connection to Azure does not work “AT+CIPSSL=1” returns “OK” the server rejects the message.
I can connect OK to normal connections (no SSL) such as “TCP”,“www.google.com”,“80”
The error I receive is :
STATE: TCP CLOSED
(where xxxxxx is the name of my Azure hub)
When I try to connect with “AT+CIPSSL=0” to any website I get a valid connection. With “AT+CIPSSL=1” I get the “STATE: TCP CLOSED, CONNECT FAIL” error.
I think the SIM868 is very similar to the rest of the SIM8xxx family. Is there a step I am missing or does it not have correct SSL certificates?
In both cases I am using the following sequence:
AT+CIPSSL=1 (or (AT+CIPSSL = 0)
The Azure SSL requirement is the “DigiCert Baltimore Root certificate”
I’m not sure if I’m supposed to set the SSL cert myself. On page 21 of this document there are some instructions but they are not clear to me.
For example the command “AT+FSCREATE=C:\USER\HENRY_SSL.CRT”, what is the “C” drive? Is it a file system created on the module?