Hardware and capacity planning

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					Hardware & Capacity planning

Data - Communication
Data-communication is the combination of data-processing and communication. It includes the processing of data of program's running on computer-systems, and the communication over great distance where the information is transported by using of electrical-conductivity, radio-waves, lightsignals, etc. With data-communication it is possible to communicate over great distances from terminals connected on the communication network.

Components of Data Communication
Three Components of Data Communication
 Data
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Analog: Continuous value data (sound, light, temperature) Digital: Discrete value (text, integers, symbols) signal

Data
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Voice Images Digital data Analog data Text Digitized voice or images

Analog Signal
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Continuous waves with no discontinuity or break in between They can travel long distances but they get distorted by noise. In long distance travel, the strength of the signal starts decreasing.

Digital Signals
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Discrete on-off pulses i.e. they present information in terms of two states of signals, either one(1) or zero(0). Any number has to be represented as a combination of ones and zeros, called binary digits (bits). Digital transmission is preferred over analog signals because of its high quality Digital signals are less affected by disturbances or noise and they can be repeatedly strengthened for long distance transmission

Advantages of Digital Transmission
The signal is exact Signals can be checked for errors Noise/interference are easily filtered out A variety of services can be offered over
one line Higher bandwidth is possible with data compression

Data Transmission
A given transmission on a communications channel between two machines can occur in several different ways. The transmission is characterized by:  The direction of the exchanges  The transmission mode: the number of bits sent simultaneously  Synchronization between the transmitter and receiver

Various Transmission Modes
A simplex connection is a connection in which the data flows in only one direction, from the transmitter to the receiver. This type of connection is useful if the data do not need to flow in both directions (for example, from your computer to the printer or from the mouse to your computer...).

A half-duplex connection (sometimes called an alternating connection or semi-duplex) is a connection in which the data flows in one direction or the other, but not both at the same time. With this type of connection, each end of the connection transmits in turn. This type of connection makes it possible to have bidirectional communications using the full capacity of the line.

A full-duplex connection is a connection in which the data flow in both directions simultaneously. Each end of the line can thus transmit and receive at the same time, which means that the bandwidth is divided in two for each direction of data transmission if the same transmission medium is used for both directions of transmission.

Asynchronous Transmission
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Transmits one character at a time, with each character followed by a start bit, Asynchronous transmission is inefficient because of the additional bits required for indicating start and stop, and an idle time between transmission of characters, It is therefore normally used for low speed data transmissions at rates below 2400 bps. Each character is preceded by some information indicating the start of character transmission (the transmission start information is called a START bit) and ends by sending end-of-transmission information (called STOP bit, there may even be several STOP bits).

Synchronous Transmission
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A group of characters is sent at a time . The start and end of a character is determined by a timing signal initiated by a sending device. thus it eliminates the need for the start and stop bits.

Communication Channel
Physical connection lines  a) TWISTED PAIR WIRES
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THEY ARE MADE UP OF COPPER AND A PAIR OF WIRES TWISTED TOGATHER TO REDUCE INTERFERENCE WITH ADJACENT WIRES. USED FOR SHORT DISTANCE (UP TO ABOUT 1KM) DIGITAL DATA TRANSMISSION. INEXPENSIVE WIDELY USED AND EASY TO IMPLEMENT THEIR USE IS LIMITED BECAUSE THEY EASILY PICK UP NOISE SIGNALS, WHICH RESULT IN HIGH ERROR RATES WHEN THE LINE LENGTH EXTENDS BEYOND 100 METERS.

b) COAXIAL WIRES
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This cable can carry much more data and is less susceptible to electrical interference. It is more expensive and relatively inflexible.

c) FIBRE OPTIC LINES Optical fiber may be used to communicate either analog or digital signals. In analog transmission, the light intensity is varied continuously whereas in digital transmission the light source is turned on or off.
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This cable consists of thousands of very thin filaments of glass. This cable is immune to electrical interferences and hence is more reliable

BANDWIDTH
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It is refer as Capacity To Transmit
a) NARROW BAND / LOW SPEED: RANGE: 300-1200 BITS PER SECOND USED FOR LOW-SPEED TERMINAL b) VOICE BAND / MEDIUM SPEED RANGE: 300-2400 BAUDS. USED IN A STANDARD TELEPHONE LINE c) BROAD BAND / HIGH SPEED INTERVAL FROM 19,200 bps TO SEVERAL BILLIONS bps. such capacities can be achieved with data transmission through coaxial cables, fiber-optic cables, microwave and satellite.

Need for Networking
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Exchange Files Share Peripherals Inter – office transactions Multiple access of data keeping pace with the latest technology


				
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