03_Communications_Internet - LECTURE 3: COMMUNICATIONS...

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Unformatted text preview: LECTURE 3: COMMUNICATIONS & THE INTERNET CSI 1306 F Computing Concepts for Business Uses for a Personal Computer As a standalone 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 Workstation with a Modem Plus Communications Software Plus Communications Software Modem Communication signals analog  continuous  frequency (cycles/second or hertz) and amplitude digital  discontinuous (discrete)  bits per second  higher speed and capacity  higher quality (less errors) regeneration, not amplification Modem Modem (modulator, demodulator) converts analog to digital (and vice versa)  sending computer (digital signal)  to modem (converts digital to analog signal)  for telephone line (carries analog signal)  to receiving modem (converts analog to digital signal)  for receiving computer (digital signal) internal or external modems  internal ones come either as onboard or separate components to the motherboard  external ones have to be plugged, usually via USB ports Communication Parameters To communicate, two computers must use the same protocol the protocol defines a set of rules that govern how two devices communicate these rules include: (1) data bits per character (1) how many bits are used to represent a character, usually 7 or 8 (2) parity  even, odd or none  a form of information redundancy in the network packets to ensure accurate detection/correction of transmission errors Communication Parameters (3) speed  data transfer rate in bits per second (for estimation purposes, assume 10 bits/character) human reading rate: 50 bps typing rate: 15 bps telephone line: 56,000 bps microwave or satellite: 500,000+ (4) flow control method  specifies the action to be taken if the buffer becomes too full to receive more data from the transmitting system (5) error detection scheme  what scheme will be enforced to detect/correct errors (e.g. CRC, parity, etc.) Transmission Media (channels) Data are transmitted in the form of electrical pulses, electromagnetic waves or pulses of light Media telephone line (electrical pulses)  twisted pair copper wire  subject to electrical interference (noise) coaxial cable (electrical pulses)  increased capacity fiber optic cable (pulses of light)  light fired by lasers as pulses through thin (1/2,000 inches) glass or plastic fibers  no electronic noise, high speed, high capacity, secure Transmission Media (channels)...
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03_Communications_Internet - LECTURE 3: COMMUNICATIONS...

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