Communication program: How to capture communication status

Communication program: How to capture the communication status-Linux general technology-Linux programming and kernel information. The following is a detailed description. In a project, data is transferred through cat dialing and telephone lines.
When the communication is suddenly interrupted, how should my program capture the information returned by the cat? Because the information returned by the cat may be processed as a data packet.
Everyone has experience in this area and hopes to give them a solution.
Self-implemented code
Of course, the source code is the best