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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) • • • • • 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 • • • • Reliability Security Privacy Humanity Email Problems • • • • • • • 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