Module will respond CLOSED in the following three conditions:
1. TCP connection is closed by the server.
2. If module still cannot receive ACK from server after re-trying to transmit data to the server for 12 times, it will automatically close TCP connection and respond CLOSED.
3. TCP connection might be interrupted and module will respond CLOSED due to the abnormality of network.
When using module’s embedded stacks like TCP and UDP protocol, you need to use AT+QICSGP to configure the APN. While using PPP, you need to use AT+CGDCONT to configure the APN.
Both UTF8 and UCS2 are supported. However, it is recommended to use UTF8 coding scheme because the network compatibility for UCS2 coding scheme is not so good.