The ability to make different TCP socket types that inherit from class `TcpSocket` and that plug into TcpL4Protocol using a factory object has been lost over time. Some discussion on ns-developers is linked [here](https://groups.google.com/g/ns-developers/c/Gk3rtlAINQk). Jayesh provided a patch, uploaded here: [TcpL4Protocol.diff](/uploads/beb36033b4bf11715890122018451cc5/TcpL4Protocol.diff) The patch seems like a reasonable start that would not affect backward compatibility.