Nonstandard TCP ports
By convention, servers running well-known Internet applications use standard, well-known TCP port numbers. By default, a HTTP server listens for requests on port 80, an FTP server listens on port 21, and so on. The port number can be omitted from a URL if the well-known port is used. Clients-such as web browsers-determine which well-known port to connect to by the protocol indicated in the URL. For example, requests for the URL http://www.ora.com are made to the host machine www.ora.com on port 80. When a nonstandard port is used, the URL must include the port number so the browser can successfully connect to the service. For example, the URL http://www.example.com:8080 connects to the web server running on port 8080 on the host www.example.com.