What are the different types of Data transmission modes in Computer Networks - MBA Notes

What are the different types of Data transmission modes. - MBA Notes

Answer:
The different types of Data Transmission modes are:
1. Serial and Parallel
2. Simplex, Half duplex and Full duplex
3. Synchronous and Asynchronous transmission

1. Serial and Parallel Transmission

Serial Transmission:

* In serial transmission one bit follows another, so we need only one communication channel rather than n to transmit data between two communicating devices.

 
* The advantage of serial over parallel transmission is that with only one communication channel, serial transmission reduces cost of transmission over parallel by roughly a factor of n.

* Serial transmission occurs in one of three ways: asynchronous, synchronous, and isochronous.

Parallel Transmission

* Binary data, consisting of 1 s and 0 s, may be organized into groups of n bits each. Computers produce and consume data in groups of bits much as we conceive of and use spoken language in the form of words rather than letters. 

By grouping, we can send data n bits at a time instead of 1 bit at a time. This is called parallel transmission. 

The mechanism for parallel transmission is a simple one: Use n wires to send n bits at one time.

 
* The advantage of parallel transmission is speed.

 
* But there is a significant disadvantage: cost. 

Parallel transmission requires n communication lines just to transmit the data stream.

2. Simplex, Half duplex and Full duplex 

Simplex

* In simplex communication mode, there is a one-way communication transmission. Television transmission is a good example of simplex communications.

 
* The main transmitter sends out a signal (broadcast), but it does not expect a reply as the receiving units cannot issue a reply back to the transmitter.

 
* Simplex circuits are seldom used because a return path is generally needed to send acknowledgement, control or error signals.

Half-duplex:

* In half-duplex mode, both units communicate over the same medium, but only one unit can send at a time. 

While one is in send mode, the other unit is in receiving mode. It is like two polite people talking to each other – one talks, the other listens, but neither one talks at the same time.

 
* Thus, a half duplex line can alternately send and receive data. It requires two wires.

Full – duplex

* In Full-duplex transmission, data is transferred in both directions.

* Use of a full-duplex line improves efficiency as the line turn-around time required in a half-duplex arrangement is eliminated. It requires four wires.

3. Synchronous and Asynchronous transmission

Synchronous Transmission

* In synchronous transmission, data transmission is tied to a clock.

The bit stream is combined into longer “frames”, which may contain multiple bytes. Each byte,

 however, is introduced onto the transmission link without a gap between it and the next one.

 
* It is left to the receiver to separate the bit stream into bytes for decoding purpose.

 
* Timing becomes very important, therefore, because the accuracy of the received information is completely dependent on the ability of the receiving device to keep an accurate count of the bits as they come in.

Asynchronous Transmission

* Asynchronous transmission is so named because the timing of a signal is unimportant.

 
* Instead, information is received and translated by agreed upon patterns. Patterns are based on grouping the bit stream into bytes.

 
* Extra bits are used to mark the beginning and end of bytes. This bit, usually a 0, is called the start bit. To let the receiver know that the byte is finished, 1 or more additional bits are appended to the end of the byte. These bits, usually 1s, are called stop bits.

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