Each time you click on a link in a web page or type an address into your web browser you are making a ‘request’ for a certain document. That request is handled with the Hyper Text Transfer Protocol (HTTP) and sent over the Internet to the server which holds the document in question. If all goes well the server responds by sending the document — usually a web page of text and graphics.
HTTP is part of the Internet Protocol (IP) suite. It is used by a ‘client’ such as a web browser to establish a connection with the server which hosts a particular website. The server waits for incoming requests by monitoring TCP port 80.
Transmission Control Protocol (TCP) is used to create connections between two computers on the Internet so they can exchange data. TCP has provisions for identifying the requesting computer and for transmitting data with time stamps so that it can be reassembled in the correct order once it arrives at its destination.
There are several TCP ports which have standardized uses. TCP port 21, for example, is usually reserved for FTP (File Transfer Protocol) for uploading and downloading files. Port 80 is usually...