PaulS:
If there are a limited number of connections (like the Ethernet shield can only handle 4 simultaneous connections), and you use one of them for a telnet session, so that you can be told twice a day that the door opened or closed, then that connection is not available for any other use. Hence it is tied up.
It that one connection is nothing, this implies, to me, at least, that it isn't 1 of 4. Rather, it is one of so many that one doesn't matter.So, which is it? Are you tying up one of a limited number of connections, where it could matter, or one of so many that it doesn't matter?
Do you not understand how a basic telnet connection works? It is nothing more than a simple TPC socket connection. It is trivial to establish the connection, send/receive data, then close the connection, leaving the sockets on both client and server "busy" for only as long as it takes to service a single client (which should be VERY quick). Having a telnet server standing by, ready to service a client at any time, consumes only ONE of the 5 available sockets, leaving the other 4 free for other uses. Such a setup can handle dozens, hundreds, even thousands of clients with a single socket, as long as they all understand they may sometimes have to wait a bit for service. And, in this case, it sounds like there would only ever BE a single client.
Regards,
Ray L.