1. COSC-100 (Elements of Computer Science) Prof. Juola
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 ( )
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
Who’s 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