CT320 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:

living-room Linux laptop
library Linux laptop
back room Linux laptop
CSU Mac laptop
wife’s Windows laptop
desktop Windows system

wife’s Android tablet
my Android phone
wife’s Android phone
NAS
Wi-Fi DD-WRT router
Wi-Fi DD-WRT repeater

Wi-Fi printer
cable modem
TV
DVR
Blu-ray player
Wi-Fi thermostat

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.

CT320: Network and System Administration

Fall 2018

Definitions