If you connect to a Server in a way like you do with telnet or some similar protokoll you may have problems with sending data to the server. I found out that at some servers there is a different between:
socket_write ($my_socket, $line, strlen ($line));
socket_write ($my_socket, "\r\n", strlen ("\r\n"));
witch worked at least, and
socket_write ($my_socket, $line."\r\n", strlen ($line."\r\n"));
wich made the server stop sending any data.
I hope this helps to save a lot of time. I needed about two days to find out, that this was the problem ;)