Only one application at a time can listen on a given port number. If you pick a port number like 80 or 8080 (two ports commonly used by web servers) and you have a web server running on your machine, your HL7 server will throw some type of exception on start up because it will not be allowed to listen to the same port.

	Using netstat -a is a really helpful command to run from a command prompt on your computer to see what applications are actively listening on what TCP/IP ports. Consult your operating system documentation for more information.