The Internet is a collection of different types of computer hardware talking to each other. The challenge is to get those different types of hardware to speak to each other. Protocols are sets of rules about how IT equipment should talk to each other. To develop Web pages you do not need to understand the protocols which get the pages to the user but some idea of what happens might come in useful. For example:
- HTTP is a protocol which sets the rules for asking for and receiving Web pages. Browsers and Web servers understand and use HTTP
- TCP is the protocol which is used to chop up data at one end into manageable pieces ready for transmission. At the other end it glues the chunks back together and makes sure there are no errors.
- IP is the set of rules which guide data to it's destination over the Internet
The three protocols in this example work together to get Web pages from Web servers to Web browsers:
- The browser follows the HTTP rules to create a request for a specific page
- That request is processed by client networking software (following TCP rules) to create packets ready to travel over the Internet
- Source and destinations addresses are added to each packet by software following the IP rules
- Each packet is guided around the Internet by routers which understand the IP rules (packets may travel by many different routes and get there at different times
- Each packet is received by networking software at the destination (IP)
- The packets are collected back together and when they are all there the data is passed to the Web server
- The HTTP software (e.g. Apache or IIS) receives and understands the request for a page and sends it to the computer which requested it following the HTTP rules
- TCP and IP are used to get the page to the system which requested it where the browser then receives the pageWeb page download as graphic
There are many other protocols in use on the Internet. Ignoring hardware protocols the most common are probably:
- Hypertext Transfer Protocol - used to request and receive Web pages and Web page components
- Post Office Protocol (POP3) - used to store mail on server ready for collection by email client
- Simple Mail Transfer Protocol - gets email from email client to mail server
- Internet Message Access Protocol - allows access to email by Web mail (although it can be used by email clients as well)
- Transmission Control Protocol - used to package and unpackage data before and after transmission
- Internet Protocol - gets the packaged data to it's destination by any route possible
- User Datagram Protocol - used mainly for ping - quick and dirty data transfer for small amounts of data
- Dynamic Name System - used to map IP addresses to domain names so that users can use names not numbers when they ask their browser for a Web page
