Jan 17, Communications and the Internet

Jan 17, Communications and the Internet -...

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Communications and the Internet 25/01/2008 15:09:00 Uses for a Personal Computer As a stand-alone workstation As a workstation with a modem As a workstation in a local area network The latter two uses involve electronic transmission of data (including voice,  picture, text and video) from one device to another Modem Communications Signals o Analogue Continuous Frequency (cycles/second or hertz) and amplitude o Digit Discontinuous (discrete) Bits per second Higher speed and capacity Higher quality (less errors) Regenerations not amplification Modem (modulator, demodulator) o Converts analogue to digit (and vice-versa) Sending computer (digital signals)
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To modem (converts digital to analogue signal) For telephone line (carrier analogue signal) To receiving modem (converts analogue to digital signal) For receiving computer (digital signal) o Internal or external modems Communication Parameters To communicate, two computers must use the same protocol o Set of rules that govern how two devices communicate o These rules include: 1. Data bits per character usually 7 or 8 2. Parity even, odd or none 3.  Speed data transfer in bits per second (for estimation purposes,  assume 10 bits/characters) human reading rate: 50 bps typing rate: 15 bps telephone line: 56,000 bps microwave or satellite: 500,000+ 4.  Flow control method
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specifies the action to be taken is the buffer becomes too  full to receive more data from the receiving system 5. Error detection scheme Transmission Media (channels) Data are transmitted in the form of electrical pulses, electromagnetic waves or  pulses of light Media o Telephone line (electrical pulses) Twisted pair copper wire Subject to electrical interference (noise) o Coaxial cable (electrical pulses) Increased capacity o Fiber optic cable (pulses of light) Light fired by lasers through thin (1/2000 inches) glass or plastic  fibers No electronic noise, high speed, high capacity, secure o Microwave (electromagnetic waves through the atmosphere) Electromagnetic waves of higher frequency than radio Relay stations 20 to 30 miles apart Used in the telephone system o Satellite (electromagnetic waves through the atmosphere) Satellite with transponders to receiving, amplify and retransmit  signals to and from earth stations Services Available
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o Email Letter or memo sent electronically from one user to another;  message is stored on the host or file server You can access the e-mail application to see it o Bulletin boards Computer connected to a modem and a phone line that allows 
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This note was uploaded on 12/08/2009 for the course TEFLER ADM1300 taught by Professor Koppel during the Fall '09 term at University of Ottawa.

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Jan 17, Communications and the Internet -...

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