08-03-2011, 10:23 AM
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Components of Data Communication
Data
Analog: Continuous value data (sound, light, temperature)
Digital: Discrete value (text, integers, symbols)
Signal
Analog: Continuously varying electromagnetic wave
Digital: Series of voltage pulses (square wave)
Analog Data-->Signal Options
Analog data to analog signal
Inexpensive, easy conversion (eg telephone)
Used in traditional analog telephony
Analog data to digital signal
Requires a codec (encoder/decoder)
Allows use of digital telephony, voice mail
Digital Data-->Signal Options
Digital data to analog signal
Requires modem (modulator/demodulator)
Necessary when analog transmission is used
Digital data to digital signal
Less expensive when large amounts of data are involved
More reliable because no conversion is involved
4-1 DIGITAL-TO-DIGITAL CONVERSION
In this section, we see how we can represent digital data by using digital signals. The conversion involves three techniques: line coding, block coding, and scrambling. Line coding is always needed; block coding and scrambling may or may not be needed.
Data Rate Vs. Signal Rate
• Data rate: the number of data elements (bits) sent in 1s (bps). It’s also called the bit rate
• Signal rate: the number of signal elements sent in 1s (baud). It’s also called the pulse rate, the modulation rate, or the baud rate.
We wish to:
1. increase the data rate (increase the speed of transmission)
2. decrease the signal rate (decrease the bandwidth requirement)
1. Worst case, best case, and average case of r
2. S = c * N / r baud
Components of Data Communication
Data
Analog: Continuous value data (sound, light, temperature)
Digital: Discrete value (text, integers, symbols)
Signal
Analog: Continuously varying electromagnetic wave
Digital: Series of voltage pulses (square wave)
Analog Data-->Signal Options
Analog data to analog signal
Inexpensive, easy conversion (eg telephone)
Used in traditional analog telephony
Analog data to digital signal
Requires a codec (encoder/decoder)
Allows use of digital telephony, voice mail
Digital Data-->Signal Options
Digital data to analog signal
Requires modem (modulator/demodulator)
Necessary when analog transmission is used
Digital data to digital signal
Less expensive when large amounts of data are involved
More reliable because no conversion is involved
4-1 DIGITAL-TO-DIGITAL CONVERSION
In this section, we see how we can represent digital data by using digital signals. The conversion involves three techniques: line coding, block coding, and scrambling. Line coding is always needed; block coding and scrambling may or may not be needed.
Data Rate Vs. Signal Rate
• Data rate: the number of data elements (bits) sent in 1s (bps). It’s also called the bit rate
• Signal rate: the number of signal elements sent in 1s (baud). It’s also called the pulse rate, the modulation rate, or the baud rate.
We wish to:
1. increase the data rate (increase the speed of transmission)
2. decrease the signal rate (decrease the bandwidth requirement)
1. Worst case, best case, and average case of r
2. S = c * N / r baud