The Internet

1
The Internet

• COSC-100 (Elements of Computer Science)
• Prof. Juola

2
Basic Concepts

• Networks -- computers communicating with each
  other
• Enables sharing of hardware, software, and data
• Network card (peripheral) connects to other
  computers, possibly through series of
  intermediaries (routers, etc.)

3
Technical issues

• Binary data (1/0) encoded as sound for modem
• Alternatively, use cable modem, DSL, wireless,
  etc.
• Several problems
• Many computers, one peripheral
• Many programs, one computer
• What do ones and zeros mean, anyway

4
Finding the target

• Most computers are hooked to routers
• Routers are like telephone switches and direct
  the bits around.
• Computers have several addresses
• Mine
• MAC address
• IP address (165.190.169.24)
• Name (shannon.mathcomp.duq.edu)

5
Finding programs

• Data is delivered to computers in packets,
  addressed by IP address and port
• Port controls what program actually gets the
  data.
• Examples
• SSH is port 22
• Mail is port 25
• Web is port 80

6
Protocols

• Meaning established by protocols each side of
  the conversation has a script

Knock Knock
Whos there?
Theseus
Theseus who?
Theseus a simple example of a protocol
7
Client/Server Computing

• Server provides service to the universe at
  large (e.g. http server, mail server)
• Client programs can connect and request
  service.
• Sample clients
• Web browsers (IE, Netscape, Mozilla)
• Mail clients (Eudora, Pine)
• Games (MMORPGs, Quake, Doom)

8
Sample protocol (http)

• Hyper Text Transfer Protocol
• Client program reads address bar
• Looks up machine name
• Requests file from server machine
• May re-request if data times out or if other data
  (e.g. animations, pictures) needed

9
Networking advantages

• Shared resources. One db, many users
• Convenient communications
• Less intrusive than telephone
• Allows time-shifting
• Better access (see on-line libraries)

10
Problems

• Reliability
• Security
• Privacy
• Humanity

11
Email Problems

• Machine failures
• Overwhelming
• Unsolicited (spam)
• Privacy threat
• Forgery
• Can be (often is) ignored
• Dehumanizing

12
Protecting yourself

• Protect your privacy (identity theft, password
  theft)
• Cross-check what you see on-line
• Limit time on-line
• Avoid information overload
• Most importantly, be aware