Internet Protocols and Addressing

For millions of different computers to communicate reliably across the Internet, they must all follow the same agreed rules. These rules are called protocols, and every device must be able to be found by a unique address.

A. Protocols. A protocol is a set of rules that governs how data is formatted, sent, and received across a network, so that the sending and receiving computers understand each other. The important Internet protocols are:

• TCP/IP (Transmission Control Protocol / Internet Protocol). This is the basic, fundamental protocol suite of the whole Internet. IP is responsible for addressing and routing — breaking data into small packets and sending each to the right address. TCP is responsible for reliable delivery — making sure all the packets arrive, in the right order, and reassembling them; if a packet is lost, TCP asks for it again.
• HTTP (HyperText Transfer Protocol) — the protocol used to transfer web pages between a web server and a browser. Its secure version, HTTPS, encrypts the data for safety and is used for banking and shopping sites.
• FTP (File Transfer Protocol) — used to transfer files (upload and download) between computers over the Internet.
• SMTP, POP, and IMAP — the protocols used to send and receive e-mail (SMTP sends mail; POP and IMAP retrieve it).

B. Addressing. Each computer and website on the Internet must be identifiable.

• IP address. Every device connected to the Internet is given a unique numerical IP (Internet Protocol) address, which identifies it on the network — for example, a set of numbers such as 192.168.1.1. It works like a postal address so that data reaches the correct device.
• Domain name. Because numeric IP addresses are hard for people to remember, each website is also given an easy-to-read domain name, such as example.gov.in. The parts after the dot (like .com, .org, .gov, .in) show the type or country of the site.
• DNS (Domain Name System). The DNS is like the Internet's telephone directory: it translates a domain name typed by the user into the numeric IP address the computers actually use, so that the user's request reaches the right server.
• URL (Uniform Resource Locator). A URL is the full address of a particular web page — for example, the protocol, the domain name, and the path to the page. Typing a URL into a browser takes the user straight to that page. …