Data Transmission Data Transmission and and

NetworksNetworksModes of Data Transmission Modes of Data Transmission

Learning ObjectivesLearning Objectives

Describe the characteristics and uses of Serial and Parallel transmission of data.Describe the characteristics of Simplex, Duplex and Half Duplex data transmission.

Data transmissionData transmission

Data needs to be transmitted between Data needs to be transmitted between devices in a computer system.devices in a computer system.Data is transmitted in the form of bits.Data is transmitted in the form of bits.So an 8 bit byte, which stands for a single So an 8 bit byte, which stands for a single character, will be transmitted in 8 parts, character, will be transmitted in 8 parts, one signal for each bit.one signal for each bit.

Modes of TransmissionModes of Transmission

There are five possible different modes There are five possible different modes of transmission.of transmission.They fall into groups:They fall into groups:

1.1. Serial / ParallelSerial / Parallel2.2. Simplex / Half Duplex / DuplexSimplex / Half Duplex / Duplex

Serial transmission of dataSerial transmission of dataOne bit transmitted at a time using a single wire. One bit transmitted at a time using a single wire. Advantage:Advantage:

Simple and reliable because the next bit is not transmitted until Simple and reliable because the next bit is not transmitted until the current one has arrived at its destination. So little or no the current one has arrived at its destination. So little or no chance of the bits arriving out or order and can be used over chance of the bits arriving out or order and can be used over long distances – see parallel transmission on the next slide for long distances – see parallel transmission on the next slide for more explanation of this.more explanation of this.

Disadvantage:Disadvantage: Slow, because only one bit can be transmitted at a time.Slow, because only one bit can be transmitted at a time.

e.g. e.g. 0110110101101101 being transmitted. being transmitted.

Parallel Transmission DiagramParallel Transmission DiagramBits sent at the same time using more than one wire.Bits sent at the same time using more than one wire.

Usually 8, so a whole byte can be sent at once.Usually 8, so a whole byte can be sent at once.Advantage:Advantage:

Faster because all the bits are Faster because all the bits are travellingtravelling at the same time. at the same time.Disadvantage: Disadvantage:

Due to fine tolerances (resistances) in the transmission, it is less Due to fine tolerances (resistances) in the transmission, it is less reliable as the bits can become muddled up (as they may arrive reliable as the bits can become muddled up (as they may arrive out of order). out of order).

The longer the wires the more effect these fine tolerances The longer the wires the more effect these fine tolerances (resistances) would have.(resistances) would have.

Simplex modeSimplex modeData can only travel in one direction.Data can only travel in one direction.Used if only one direction is necessary.Used if only one direction is necessary.

e.g. Television picture which is passed to a television receiver e.g. Television picture which is passed to a television receiver aerial, but there is no way to send data in the other direction. aerial, but there is no way to send data in the other direction.

N.B. Not modern interactive digital television.N.B. Not modern interactive digital television.

Transmitter Receiver

Half duplex modeHalf duplex mode

Data can pass in both directions, but only in one Data can pass in both directions, but only in one direction at a time.direction at a time.Used if both directions are necessary but not at Used if both directions are necessary but not at the same time.the same time. e.g. CB radio system in which each handset can e.g. CB radio system in which each handset can

either be set to receive mode or send mode. either be set to receive mode or send mode.

Device 1 Device 2

Duplex mode Duplex mode

Data can pass in both directions at the same Data can pass in both directions at the same time.time.Used if both directions are necessary at the Used if both directions are necessary at the same time.same time. e.g. A telephone conversation as both users can e.g. A telephone conversation as both users can

speak and be heard at the same time. speak and be heard at the same time.

Device 1 Device 2

PlenaryPlenary

Can you explain the difference between Serial and Parallel transmission of data? Serial

One bit transmitted at a time using a single wire.One bit transmitted at a time using a single wire. ParallelParallel

Bits sent at the same time using more than one Bits sent at the same time using more than one wire.wire.

PlenaryPlenary

Can you explain Simplex, Duplex and Half Duplex data transmission? Simplex

Data can only travel in one direction.Data can only travel in one direction. Duplex

Data can pass in both directions at the same time.Data can pass in both directions at the same time. Half Duplex

Data can pass in both directions, but only in one Data can pass in both directions, but only in one direction at a time.direction at a time.

Asynchromous TransmissionAsynchromous Transmission

Synchronous TransmissionSynchronous Transmission