The basic picture
A computer network is a group of computers and devices connected so they can exchange data. Connecting a handful of machines in one office is quite different from connecting millions around the world, but many of the same words apply to both. The vocabulary below follows a message from its source to its destination.
Networks and their sizes
- Network. Any set of connected devices that can exchange data.
- LAN. Short for local area network, a network covering a limited area such as a building. Local area networks became common in offices and schools during the 1980s.
- WAN. Short for wide area network, covering a large geographic area, often by linking smaller networks together.
- Internet. A worldwide system of networks that exchange data using shared rules. The name comes from “internetwork,” meaning a network of networks, and the idea took shape between the 1960s and 1980s, building on research networks such as ARPANET.
- Intranet. A private network that uses internet technology but is limited to an organization.
The rules of communication
A protocol is an agreed set of rules for how two systems exchange data. Like the etiquette of a phone call, with greetings and turn-taking, a protocol defines how a conversation begins, how information is formatted and how errors are handled. Protocols let machines from different makers talk to each other, since each side follows the same published rules.
The central rules of the internet are often called internet protocols. Two names appear constantly. IP, or Internet Protocol, deals with addressing and forwarding data. TCP, or Transmission Control Protocol, is commonly used alongside it to help data arrive complete and in order. Together they are often written TCP/IP. Other protocols sit on top for particular jobs, such as HTTP for web pages and SMTP for sending email.
Packets and routing
A packet is a small, labeled chunk of data. Rather than sending a whole message as one unbroken stream, many networks break it into packets, send them separately and reassemble them at the destination. This approach is called packet switching, and it was developed through research in the 1960s by several groups, so credit is shared rather than belonging to one person.
A router is a device that receives packets and forwards them toward their destinations, often across several links. A switch does a similar job inside a local network, directing data between devices on that network. An older device called a hub simply repeated data to every connected device. A gateway connects networks that use different rules or sit under different control.
Addresses and names
- IP address. A numeric label that identifies a device on a network. It is similar to a postal address, because it tells other devices where to send data.
- Domain name. A readable name, such as example.org, that stands in for a numeric address. People find names easier to remember than strings of digits.
- DNS. The Domain Name System, which translates domain names into numeric addresses. It was introduced in the 1980s to replace a manually maintained list of names. It is often compared with a phone book, although it is distributed across many servers.
- Top-level domain. The last part of a domain name, such as .com or .org.
- URL. A Uniform Resource Locator, the full address of a page or file, including the protocol and the location.
Clients, servers and the web
A server provides data or a service. A client requests it. These are roles, not types of machine, and one computer can be both at different times. When you load a page, your browser acts as a client and the site’s computer acts as a server. The pages themselves are part of the World Wide Web, which runs on top of the internet and is not the same thing as the internet.
A web browser is the program that retrieves and displays web pages. Hosting means providing the server space that keeps a site available. A firewall is software or hardware that filters network traffic according to rules, named after the barriers used in buildings and vehicles to slow the spread of fire.
Speed and quality
- Bandwidth. The amount of data a connection can carry in a given time, usually measured in bits per second. The word originally described a range of signal frequencies, and it later shifted to mean capacity.
- Latency. The delay before data begins to arrive. A connection can have high capacity and still feel slow if latency is high.
- Broadband. A general term for faster connections than traditional dial-up telephone modems, although what counts as fast has changed over time.
A word of caution
Networking vocabulary is used loosely in everyday speech. People say “the internet is down” when they mean one service, or “the web” when they mean the internet. In technical writing the distinctions matter, because a problem in a router, a protocol or a domain name each calls for a different explanation. When reading older material, remember that some terms, especially “network” and “internet,” had narrower meanings at the time than they do now.