Explain the asynchronous transmission and synchronous transmission in brief. Or Compare the overhead in an asynchronous system versus a synchronous ssystem. How is the overhead partitioned in each ? Which is more efficient, in terms of the overhead to send several characters? Why.

Explain the asynchronous transmission and synchronous transmission in brief. Or Compare the overhead in an asynchronous system versus a synchronous ssystem. How is the overhead partitioned in each ? Which is more efficient, in terms of the overhead to send several characters? Why.

Ans. Asynchronous Transmission- In the Asynchronous Transmission

the timing of a signal is unimportant. Instead, information is received and

translated by agreed-upon patterns. As long as those patterns are followed,

the receiving device can retrieve the information without regard to the rhythm

in which it is transmitted. Patterns are based on grouping the bit stream into

bytes. Each group, generally of eight bits, is ttransmitted along the link as a

unit. The sending system handles each group independently relaying it to the

link whenever ready, without regard to a timer.

 

The receiver cannot use timing without a synchronizing pulse, to predict

when the next group will arrive. Thus, an extra bit is added at the starting of

each byte to alert the receiver to the arrival of a new group. this bit, generally

a 0, is known as the start bit.

 

One or more additional bits are appended to the end of the byte to let the

receiver know that the byte is finished. These bits, usually Is, are known as

stop bits. By this technique, each byte is increased in size to at least 10 bits of

which 8 are information and 2 or more are signals to the receiver. Then, the

transmission of each byte may be followed by a gap of varying  duration. This

gap can be represented either by an idle channel or by a stream of additional

stop bits.

end of each byte and permit it to synchronize with the data strength. Th1s

mechanism is known as asynchronous because, sender and the rece1ver do

not have to be synchronized at the byte level. But within each byte, the receiver

must still be synchronized with the incoming bit stream. It means that some

synchronization is needed, but only for the duration of a single byte. !he

receiving device resynchronizes at the onset of each new byte. If the rece1~er

detects a start bit then it sets a timer and starts counting bits as they come in.

After n bits the receiver looks for a stop bit. As soon as it detects the stop bit,

 

The start and stop bits and the gap alert the receiver to the starting and

end of each byte and permit it to synchronize with the data stream. Th1s

mechanism is known as asynchronous because, sender and the receiver do

not have to be synchronized at the byte level. But within each byte, the receiver

must still be synchronized with the incoming bit stream. It means that some

synchronization is needed, but only for the duration of a single byte. the

receiving device resynchronizes at the onset of each new byte. If the receiver

detects a start bit then it sets a timer and starts counting bits as they come in.

After n bits the receiver looks for a stop bit. As soon as it detects the stop bit,

it ignores any received pulses until it detects the next start bit.

An example of asynchronous transmission is shown in fig. 2.3, in which

the start bits are 0s, the stop bits are 1s, and the gap is represented by an idle

line rather than by additional stop bits.

Due to addition of stop and start bits and the insertion of gaps into the bit

stream, the asynchronous transmission becomes slower than forms of

transmission which can operate without the addition of control information. It

has two advantages that it is cheap and effective, which make it an attractive

choice for situations like low-speed communication.

example of asynchronous transmission

Synchronous Transmission – This type of transmission uses the bit

Stream combined into longer “frames”, which may contain multiple bytes.

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