I'm so confused when my mobile phone sends a text message to Unicom! !

Short message reporting between different operators is inaccurate, that is to say, although you received a short message reporting that it was sent successfully, it was actually not sent successfully, and your classmates did not receive your short message.

I guess this short message reporting mechanism should send a message to your mobile phone when the short message leaves the operator's network. So when your short message leaves the mobile network and enters Unicom, the mobile network will send a short message report to your mobile phone, prompting you to receive it, but in fact, after the short message entered Unicom, it was not received because of downtime.

I wonder if you can understand this.