The bc28 module connects to the private mqtt server at a very slow speed, usually around 5 minutes. However, when using coap to connect to the telecom cloud server, the connection time is basically negligible. Compared with China Mobile nb card and China Telecom nb card, the results are basically the same.
The reason is that MQTT USES domain name links, which involve problems with DNS servers.The module has default DNS resolution address and alternate address.
Under normal circumstances, when the terminal device is working on site, the base station will issue DNS domain name resolution address to the module, and the module will modify its default domain name resolution address.However, if the base station does not send DNS resolution address to the module, the module will first use its default DNS resolution address to resolve, and if the resolution fails, the module will use the alternate DNS resolution server address to resolve.This can lead to long parsing times.
感谢您的回复，有解决办法吗？比如采用ip地址连接就OK吗？
There is no problem with using IP addresses.
You can use AT+QIDNSCFG= to configure the DNS domain name you find useful for resolving server addresses