Changhong M658 single card mobile phone, what does the "reply path" of SMS mean?

Message reporting: A sends a short message to B, and A starts message reporting. When B receives the short message sent by A, the service center will inform A that the message has been sent successfully, which is to help you ensure that the short message has been received by the other party, not as shown on your own mobile phone.

Reply path: This is more complicated. It needs to use the network service center where the two mobile phones are located, and the routing will be different. And it needs the difference of operators, and there is basically no difference at present.