Appendix
© 1998 NWU
Please send comments
and requests
for
additional copies
of this
report to
metrochicago@nwu.edu.
APPENDIX
AN INTRODUCTION TO DIGITAL NETWORKING Digital Bits and Bytes
The basic unit of digital information is the binary digit, or bit. A bit can be thought of as a switch that is either on or off and can represent two values (0, 1). Bits are combined to represent more than two values. For example, the four possible combinations of two bits (00, 01, 10, 11) can be used to represent four values. In general, n number of bits can be used to represent 2n values. Four bits can represent 24=16 values, eight bits can represent 28 (2 to the eighth power) = 256 values.Digital Information
When text, pictures/graphics, sound, or video/film is digitized, it is represented as a series of numbers. This series of numbers can be converted into a series of digital bits that can be used to recreate the original.175 –> 10101111
212 –> 11010100
Digitizing Text
In order to digitize text, each character is converted into a number which can be represented by a series of bits. The ASCII standard (American Standard Code for Information Exchange) assigns a specific number to each character. For example:
Digitizing Graphics
In order to digitize a picture, the picture is divided into a very fine grid. Each box of the grid, or pixel (picture cell), is assigned a color and intensity that can be represented by a specific value. The computer can color the pixels of the grid so quickly that it is seen as a still image.
The finer the grid, the more pixels will be used to create the picture. The picture will look better because there is more information. The greater the number of different colors that can be represented, the better the picture will look.
Digitizing Sound
In order to digitize sound, the continuous sound wave that you may have seen on an oscilloscope is divided into very short durations of time. The intensity of the sound wave is measured for each duration. Each value is represented by a number.
The interval between each sample of the sound wave must be very small to avoid distortion. The greater the number of samples, the more realistic the sound.
Digitizing Moving Images
The moving images of video and film are created by displaying a new image or frame every 1/30 second (video) or 1/24 second (film). In order to digitize video or film, each frame is digitized as a still picture.
Playing back video/film requires redrawing a new frame every 1/30 second while playing the accompanying audio.
The Common Digital Network Infrastructure
When text, graphics, sound, and moving images are converted to a common form of digital information (0s and 1s), they can be transported across the same digital network infrastructure as a series of bits.Bandwidth is a term used to indicate how much information can be transported across a digital network. The more bits that can be sent across the digital network per second, the greater the bandwidth.
The greater the bandwidth, the faster (i.e. in the shorter time) text and images can be transported across a digital network. If there is not sufficient bandwidth, sound and moving images will be interrupted or distorted.
Networking
Information is sent between computers in packets of 1,000 bytes of information. If there are more than 1,000 bytes of information, the information is broken up into multiple packets.
A hub has ports that connect individual computers to a common Local Area Network (LAN).
Each computer on the network is given a unique node address, usually between 1 and 254, that identifies the computer on the Local Area Network (LAN).
Each Local Area Network (LAN) has a unique world-wide network address. A network address is three numbers separated by a period (123.456.78).
The IP Address for a computer is the combination of the network address and the node address: 123.456.78.9. The IP Address is used to indicate the destination of each packet of information sent on the digital network.
A Router or Switch is used on each Local Area Network to send each packet to the appropriate computer. The router or switch is also used to connect Local Area Networks together.
A Backbone Network is used to connect multiple Local Area Networks together, not individual computers. The backbone network has its own unique network address.
The backbone network typically provides the greatest bandwidth to locations with the greatest network demand. These locations can serve local computers, as well as other locations that have lower bandwidth requirements.
The following diagram shows a hypothetical community network. High bandwidth rings connect high demand locations. High demand locations connect lower demand locations.
