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Networking definitions

Definition: definition

• I’m going to present definitions of several terms.
• Other sources (e.g., the Chicago Manual of Style, the Associated Press Stylebook, the MLA Handbook, etc.) will disagree.
• I’m right, they’re wrong.
• More precisely, I’m defining terms as part of technical jargon, which often disagrees with common usage.
• For example, my wife once informed me that there is “no such thing as a vegetable”. From her point of view as a horticulturist, she is correct. However, common usage disagrees with her.

Definition: host

A host is a thing on a network; anything with an IP address. My house contains these hosts:

Definition: medium

• A medium is a single means of transmitting information, including:
  • Cat-5 cable
  • cable-tv cable
  • fiber-optics
  • phone lines
  • power lines
  • lasers
  • short-wave radio
  • Wi-Fi
  • infrared light (same medium as previous three?)
  • sub-space pulses

Singular: “medium”
Plural: “media”

Definition: network

A network is hosts connected by a single medium. Your laptop and eBay are not on the same network.

    ┌────────┐           ┌────────┐              ┌─────────┐
    │        │           │        │              │         │
    │ laptop │···········│ router │··············│ Blu-Ray │
    │        │   Wi-Fi   │        │   Wi-Fi      │         │
    └────────┘           └────────┘              └─────────┘

Definition: LAN

• A LAN is a Local Area Network; a small-scale network.
• I have two LANs in my house: wired & wireless.
• Ethernet ≠ LAN
• Ethernet ⊂ LAN

Variations on a theme

• No new ideas:
  • BAN: Body Area Network
  • CAN: Campus Area Network
  • HAN: Home Area Network
  • LAN: Local Area Network
  • MAN: Metropolitian Area Network
  • NAN: Near-me Area Network
  • PAN: Personal Area Network
  • SAN: Storage Area Network
  • WAN: Wide Area Network

Definition: internet

What is a (lower-case “i”) internet(work)? It’s a collection of connected networks.

    ┌────────┐           ┌────────┐              ┌─────────┐
    │        │           │        │              │         │
    │ laptop │···········│ router │··············│ printer │
    │        │   Wi-Fi   │        │   ethernet   │         │
    └────────┘           └────────┘              └─────────┘

• I have an internet at home:
  • Wi-Fi (wireless)
  • Ethernet (wired)

Definition: Internet

What is the (upper-case “I”) Internet? It’s all the connected networks in the world. There are many internets, but only one Internet.

    ┌────────┐           ┌────────┐              ┌──────┐
    │        │           │        │              │      │
    │ laptop │···········│ router │··············│ eBay │
    │        │   Wi-Fi   │        │   Internet   │      │
    └────────┘           └────────┘              └──────┘

or, more simply:

    ┌────────┐              ┌──────┐
    │        │              │      │
    │ laptop │··············│ eBay │
    │        │   Internet   │      │
    └────────┘              └──────┘

Definition: World-Wide-Web

Tim Berners-Lee

What is the (World-Wide-)Web? It’s a use of the Internet.

• The Web is built on top of the internet.
• My personality is built on top of my brain.

Definition: End system

    ┌────────┐              ┌──────┐
    │ laptop │··············│ eBay │
    └────────┘   Internet   └──────┘

• Consider a web browser, on your laptop, connected to ebay.com.
• The laptop and the web server are both end systems, or hosts.
• End systems can also include printers, surveillance cameras, cell phones, and generally any device using the network to communicate.
• End systems are located at the network edge and connected to the network using communication links.
• Routers are not usually considered end systems.

Definition: Client/Server

    ┌────────┐              ┌──────┐
    │ laptop │··············│ eBay │
    └────────┘   Internet   └──────┘

End systems may be classified as clients, servers, both, or neither.

• Client: a program that requests services:
  • web browser requests a page
  • email reader requests messages
  • scp program requests files
  • Dropbox client stores and fetches files
• Server: a program that listens for requests and provides services
  • web server, email server, ssh server, etc.

Client vs. server depends on what programs the end system is running. A given host may be both. Most hosts are DNS clients.