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DCN :: T A -
1. what is meant by data
communication and explain its
characteristics
ANS
Data communication is the electronic
exchange of data between two devices across
a communication channel like a wire pair
cable or Fiber optics. In this article, we have
shared all the details about data
communication.
Only when communicating devices are part of a hardware and software-based communication system do data communications occur. In a computer, Data communication allows electronic or digital data to be sent between two or more devices regardless of
their geographical location, transmission medium, or data substance. The message, sender, receiver, transmission medium, and protocol are all crucial elements in data communication. ⦿ Characteristics of Data Communication Data communication has four critical characteristics that are as follows:
- Delivery
- Accuracy
- Timeliness
- Jitter ► Delivery Data must be sent in the correct order from the source device to the correct destination. ► Accuracy: The information must be supplied without errors. The data should be retransmitted if there is any inaccuracy during transmission. ► Timeliness: Data must be given within the timeframe provided. The data that was given late has become unusable. ► Jitter: Jitter is caused by an uneven or unexpected delay in the packet arrival time. 2.WRITE ABOUT DIFFERENT TRANSMISSION MODES
2. Half-Duplex Mode – In half-duplex mode, each station can both transmit and receive, but not at the same time. When one device is sending, the other can only receive, and vice versa. The half-duplex mode is used in cases where there is no need for communication in both directions at the same time. The entire capacity of the channel can be utilized for each direction. Example: Walkie-talkie in which message is sent one at a time and messages are sent in both directions. Channel capacity=Bandwidth * Propagation Delay
3. Full-Duplex Mode – In full-duplex mode, both stations can transmit and receive simultaneously. In full_duplex mode, signals going in one direction share the capacity of the link with signals going in another direction, this sharing can occur in two ways: - Either the link must contain two physically separate transmission paths, one for sending and the other for receiving. - Or the capacity is divided between signals traveling in both directions. Full-duplex mode is used when communication in both directions is required all the time. The capacity of the channel, however, must be divided between the two directions. Example: Telephone Network in which there is communication between two persons by a telephone line, through which both can talk and listen at the same time. Channel Capacity=2* Bandwidth*propagation Delay
- Amplitude Shift Keying In this conversion technique, the amplitude of analog carrier signal is modified to reflect binary data. When binary data represents digit 1, the amplitude is held; otherwise it is set to 0. Both frequency and phase remain same as in the original carrier signal.
- Frequency Shift Keying In this conversion technique, the frequency of the analog carrier signal is modified to reflect binary data.
This technique uses two frequencies, f1 and f2. One of them, for example f1, is chosen to represent binary digit 1 and the other one is used to represent binary digit 0. Both amplitude and phase of the carrier wave are kept intact.
- Phase Shift Keying In this conversion scheme, the phase of the original carrier signal is altered to reflect the binary data.
Analog-to-Analog Conversion Analog signals are modified to represent analog data. This conversion is also known as Analog Modulation. Analog modulation is required when bandpass is used. Analog to analog conversion can be done in three ways:
- Amplitude Modulation In this modulation, the amplitude of the carrier signal is modified to reflect the analog data.
Amplitude modulation is implemented by means of a multiplier. The amplitude of modulating signal (analog data) is multiplied by the amplitude of carrier frequency, which then reflects analog data. The frequency and phase of carrier signal remain unchanged.
In the modulation technique, the phase of carrier signal is modulated in order to reflect the change in voltage (amplitude) of analog data signal. Phase modulation is practically similar to Frequency Modulation, but in Phase modulation frequency of the carrier signal is not increased. Frequency of carrier is signal is changed (made dense and sparse) to reflect voltage change in the amplitude of modulating signal
