Post on 22-Dec-2015
Information & Communication
Generation and transfer of information is critical to today’s businesses
Flow of information both mirror and shape organizational structures
Networks are the enabling technology for this process
The “Manager’s Dilemma”
Technology is necessary for competitiveness Cost of technology has decreased Reliance on technology has increased Number of choices have increased Choices are both more difficult and more
important
Transmission of Information
Transmission and transmission media e.g. twisted pair, fiber, wireless, coax
Communication Techniques encoding, interface, protocols
Transmission efficiency multiplexing, compression
Telecommunication
Uses electricity to transmit messages Speed of electricity dramatically extends reach
Sound waves: ~670 mph Electricity: ~186,000 (speed of light)
Bandwidth= information-carrying capacity of a channel
Data Communication
Adding storage overcomes time constraints Store-and-forward communication
E-mail, voice mail, facsimile, file transfer, WWW
Analog Data
Continuous signal Expressed as an oscillation (sine wave
format) of frequency Example: Analog electrical signal generated
by a microphone in response to continous changes in air pressure that make up sounds
Basic Analog Terms
Wave frequency: Number of times a cycle occurs in given time period
Wave amplitude: Height of a wave cycle Hertz: The number of times a wave cycle
occurs in one second (commonly used measure of frequency)
Analog Signaling
represented by sine waves
time(sec)
amp
litu
de
(vo
lts)
1 cycle
frequency (hertz)= cycles per second
phase difference
Digital Data
Represented as a sequence of discrete symbols from a finite “alphabet” of text and/or digits
Rate and capacity of a digital channel measured in bits per second (bps)
Digital data is binary: uses 1s and 0s to represent everything
Binary digits can be represented as voltage pulses
Basic Digital Terms
Bit: digit in a binary number 1 is a 1-bit number (=1 in base 10) 10 is a 2-bit number (=2 in base 10) 10011001 is an 8-bit number (=153 in base 10)
Byte: eight bits
Converting Voice
What makes sound? Vibration of air How can we record that vibration? How can we convert that to an electrical
signal?
Analog Voice Communication Primarily used for transmission of human voice
(telephony) Microphone captures voice vibrations, converts them to
waves than can be expressed through variations of voltage Examples
Telephone (3000Hz) Hi-Fi Sound (15,000Hz; approximate range of human ear) Compact Disc (20,000Hz for each of two channels)
Digital Voice Communication For good representation, must sample amplitude at a rate
of at least twice the maximum frequency Measured in samples per second, or smp/sec Telephone quality: 8000smp/sec, each sample using 8 bits
8 bits * 8000smp/sec = 64kbps to transmit
CD audio quality: 44000smp/sec, each sample using 16 bits 16 bits * 44000smp/sec = 1.41mbps to transmit clearly
Converting Images
Break image up into small units More units means more detail Units called pixels
Use photocell to read each unit, assign value How can we represent those units electrically? PACMAN example
Image Quality Issues
More pixels=better quality More compression=reduced quality
“Lossy” gives from 10:1 to 20:1 compression “Lossless” gives less than 5:1
Less compression=reduced speed of transfer Choices in imaging technology, conversion, and
communication all affect end-user’s satisfaction
Video Communication
Sequences of images over time Same concept as image, but with the dimension of
time added Significantly higher bandwidth requirements in
order to send images (frames) quickly enough Similarity of adjacent frames allows for high
compression rates
Data Communication
In this context, we mean data stored on computers
Already digital, so no conversion necessary Bandwidth usually affects speed, but not
quality Examples?