Data transmission (also known as the digital transmission) is the process of physical transfer of a digital bit stream i.e. data over the point – to – point communication channels such as the optical fibers, wireless channels, copper wires etc.
Data can be in any of the following forms:
1. Electromagnetic signal
2. Electrical voltage
4. Radio wave
5. Infrared signals
Types of Data Transmissions
1. Analog Transmission:
– It involves transmission of analog signals that are continuously varying.
– Sequence of pulses represents these messages either by base-band transmission or pass-band transmission through a digital modulation method.
– Modem is the equipment that carries out the pass-band modulation and demodulation.
– Digital messages originating from a device or analog signals from video or phone calls are converted in to bit streams using source coding schemes and pulse – code modulation.
2. Base-band and Pass-band Transmissions:
– Base-band transmission or the digital–over–digital transmission is a sequence of pulses is produced with the help of line coding schemes (one example is line coding).
– This type of transmission is followed in the local area networks (Ethernet typically), optical fiber communication and serial cables.
– The result is a pulse amplitude modulated signal called the pulse train.
– Pass-band transmission or the digital – over – analog transmission is the digital bit stream which is modulated sine wave signal. PSK, FSK, QAM are all modulation methods used for producing signals here.
– Usually, used in cable TV networks and wireless communications.
3. Serial Transmission:
– When the single elements of a data entity are transmitted sequentially, it is called the serial transmission.
– Bits are transmitted over optical path or wire sequentially.
– The requirement for signal processing is reduced along with the error possibilities when compared to the parallel transmission.
– Also, the transfer rate is faster than for each individual path.
– This makes is appropriate to be used over longer distances for sending the parity bit.
4. Parallel Transmission:
– It involves simultaneous transmission of the signal elements of the data entity over two or more paths.
– For example, multiple electrical wires over which bits can be transferred simultaneously allowing higher data transfer rates.
– This kind of transmission is deployed usually in the internal buses in computers and sometimes in external devices such as printers.
– ‘Skewing’ represents a major issue in parallel data transmission because all the wires possess different properties.
– This produces variations in the arrival timings of the bits which can lead to the corruption of message.
– All this can be reduced with the help of a parity bit.
5. Asynchronous Transmission:
– In this type of data transmission, the start and stop bits are used for signifying the beginning and the end of the bit.
– 10 bits are used for the transfer of the ASCII characters.
– This type of data transmission is well suited for the situations where there is an intermittent transmission of data.
– It is a must that the polarity of the start and stop bits must be opposite so that the receiver can recognize the arrival of the second information packet.
6. Synchronous Transmission:
– This type of data transmission is completely different from the asynchronous transmission i.e., it does not make use of start and stop bits.
– Rather, it uses synchronization of the transmission speeds at both the ends between which the transmission takes place.
– This it does using the clock signals that has been incorporated in to each component.
– Data is sent as a continuous stream between the two ends.
– The data transfer rate is high but there are more errors since the clocks get out of sync and the device would follow wrong time.
– Such problems can be avoided by the re – synchronization of the clocks and using check digits.
– Both of these ensure the correct interpretation of the byte.