How Data (Binary bit stream or digitized analog signal) is transferred from one conducting node to another in a communication channel. Some of these channels are physical wires like copper wires, optical wires or wireless communication using electromagnetic waves such as radio wave, microwave, and an infrared signal. Data transmission can be a digital or analog transmission.
Data transmission of data is where the discrete message bits are transferred over an analog or digital channel. The message bits are represented by Line Code, which is produced using a digital modulation technique.
In asynchronous digital data transmission, start and stop bits are used which are of opposite polarity to represent the beginning and end of data stream. Synchronous transmission uses clock signal and checks bits at the both ends of the communication system for data transfer.
Let’s now discuss to understand the techniques of transferring the data.
i) Digital to Analogue
Digital data is converted to an analogue signal for transmission via analogue media. Three types of digital-to-analogue conversions
a) Amplitude Shift Keying
The amplitude of the analogue sinusoidal carrier is modified to represent discrete binary data. For binary data 1, a fixed amplitude carrier is transmitted otherwise it is set to 0.
b) Frequency Shift Keying
The frequency of the analogue sinusoidal signal is modified to represent discrete binary data. Here two distinct carrier frequencies are chosen to represent binary data 1 and 0, which are transmitted accordingly.
c) Phase Shift Keying
The phase of the analog sinusoidal signal is altered to represent binary data. The phase of the carrier changes when a new binary digit is encountered.
Analog signal is modified to represent analog data. Three types of analogue-to-analogue conversions
a) Amplitude Modulation
The amplitude of the modulating signal is multiplied with an amplitude of carrier signal to represent analog data.
b) Frequency Modulation
The frequency of the carrier signal is modified to represent analog data.
c) Phase Modulation
The phase of the carrier signal is modified to represent a change in voltage levels of analog signal.
Data Transmission through Electrical Conductors
Binary bits are represented by the voltage or current level. Voltage or current level within the desired range is called logic level. All digital data are represented by 1 or 0. 1 is called the logic high level and is represented by a high voltage in the wire. 0 is called the logic low level and is represented by a low voltage level in the wire. For synchronization during data transfer, flip-flops are used which are logic devices and act as a latch holding the last bit of information transferred.
Data Transmission through Public Internet
All information is represented in terms of binary data, 1 and 0 in this wireless transmission mode. The whole message stream is sliced into packets. Each packet contains a label, which has the destination address, sender’s address and sequence number. In a network, the message bits don’t reach the destination in a sequence. The receiver reassembles the packets received in terms of sequence number. Each network contains a specialized computer called router, which decides the most efficient path for packet transfer. There are several routers, which the packet encounters in its network path. Routers keep a copy of the packet transferred until it is acknowledged by the receiver. It helps in data recovery in case the data is lost and can be re-transmitted. There are several protocols that govern the wireless transmission. It ensures that the complete message can only be decoded by the rightful receiver.
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