Data Transmission (Cambridge (CIE) O Level Computer Science)
Revision Note
Written by: Robert Hampton
Reviewed by: James Woodhouse
What is data transmission?
Data transmission is the process of transferring data from one device to another using a wired or wireless connection
Wired data transmission can be completed in two ways:
Serial
Parallel
Serial & Parallel Transmission
What is serial & parallel transmission?
Serial and parallel are methods of transmitting data (bits) from a sender to a receiver
Each method determines how many bits can be transmitted at once
Serial transmission
A stream of bits is sent in sequence, one after the other
USB is an example of a wired serial connection
Parallel transmission
A stream of bits is sent in sequence, one after the other across multiple wires at the same time
Transmission is asynchronous, data does not always arrive at the same time
A skew can be caused by data arriving out of order in asynchronous transmission
A traditional printer cable is an example of a wired parallel connection
Advantages and disadvantages of serial & parallel transmission
Transmission | Advantages | Disadvantages |
|---|---|---|
Serial |
|
|
Parallel |
|
|
Simplex, Half-Duplex & Full-Duplex Transmission
What is simplex, half-duplex & full-duplex transmission?
Simplex, half-duplex and full-duplex control the direction in which data is transmitted between a sender and receiver
Simplex transmission
Data travels in only one direction
Sending data from a computer to a monitor is an example of simplex transmission
Half-duplex transmission
Data can travel in both directions, but not simultaneously (bi-directional)
A printer cable which waits for the data to be received before sending back a ‘low ink’ message is an example of half-duplex transmission
Full-duplex transmission
Data can travel in both directions at the same time (bi-directional)
Network cables can send and receive data at the same time and are examples of full-duplex data transmission
Full-duplex is used in local and wide area networks
Advantages and disadvantages of simplex, half-duplex & full-duplex transmission
Transmission | Advantages | Disadvantages |
|---|---|---|
Simplex |
|
|
Half-duplex |
|
|
Full-duplex |
|
|
Wires can be combinations of serial, parallel, simplex, half-duplex and full-duplex
Simplex | Half-duplex | Full-duplex | |
|---|---|---|---|
Serial | Serial-Simplex | Serial-Half-duplex | Serial-Full-duplex |
Parallel | Parallel-Simplex | Parallel-Half-duplex | Parallel-Full-duplex |
Serial-Simplex
Data is transmitted one bit at a time in a single direction on one wire
Serial-Half-duplex
Data can be transmitted in both directions on a single wire but only one bit at a time can be transmitted in one direction at a time
Serial-Full-duplex
Data can be transmitted in both directions at the same time on a single wire one bit at a time
Parallel-Simplex
Multiple wires transmit one bit at a time in one direction
Parallel-Half-duplex
Multiple wires send multiple bits of data in both directions but only one direction at a time
Parallel-Full-duplex
Multiple wires send multiple bits of data in both directions at the same time
Worked Example
A company has a website that is stored on a web server
The company uses parallel half-duplex data transmission to transmit the data for the new videos to the web server.
Explain why parallel half-duplex data transmission is the most appropriate method.
[6]
Answer
Parallel would allow for the fastest transmission [1]
as large amounts of data [1]
can be uploaded and downloaded [1]
but this does not have to be at the same time [1]
Data is not required to travel a long distance [1]
Therefore, skewing is not a problem [1]
Examiner Tips and Tricks
Any four of these points qualifies as a full answer, however make sure your answer is cohesive.
Saying “Parallel would allow for the fastest transmission but this does not have to be at the same time” would qualify as one mark as only the first part makes sense and follows logically
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