Download Inside the CPU - Duquesne University

The Internet
COSC-100 (Elements of Computer
Science)
Prof. Juola
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.)
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
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)
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
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
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)
Sample protocol (http)
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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
Networking advantages
• Shared resources. One db, many users
• Convenient communications
• Less intrusive than telephone
• Allows time-shifting
• Better access (see on-line libraries)
Problems
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Reliability
Security
Privacy
Humanity
Email Problems
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Machine failures
Overwhelming
Unsolicited (spam)
Privacy threat
Forgery
Can be (often is) ignored
Dehumanizing
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