Data Transmission

Data transmission is the process of transferring data from one point to another.​
​It is an extremely important process in computer science, think about it... what good would your keyboard be if your key stroke was not transferred to the CPU and then to your monitor...  Your smart phone would look a little less smart if it could not make phone calls, send text messages or connect to the internet.

Methods of Transmission

There are a number of different ways in which data can be transmitted from one point to another:
  • Copper Cable
  • Wireless (Radio Frequency)
  • Infra red
  • ​​Fiber Optic

Speed of Transmission

Nobody likes waiting around, so when setting up new technology or purchasing a new piece of equipment that involves some sort of data transmission, it is always wise to check exactly how fast it can get your data from A to B..
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The amount of data that can be transmitted at one time is referred to as its BANDWIDTH.

Serial and Parallel Transmission

Serial Data Transmission​

Serial data transmission involves one signal being sent at a time over a single wire.

​USB uses serial transmission  (Universal SERIAL Bus)

​Very high data transfer speeds can be achieved

Parallel Data Transmission

Parallel transmission involves a number of parallel wires that allow signals to be sent simultaneously.

Skew / Syncronization errors

Skew is a disadvantage of parallel transmission. Skew is caused by the fact that each wire in a parallel transmission setup will have slightly different properties.  This will mean that each signal will travel at a slightly different speed therefore arriving at their destination at different times.

Due to this, parallel transmission is best suited for situations where data is to be sent over a very small distance

The greater the distance, the greater of an issue that Skew can cause.  You can compare this to a running race...

Think about a short distance race like the 100m sprint.  In this type of race we have 8 parallel lanes and 8 runners.  Imagine that the runners are the data and the lanes are the parallel cables.  When the runners (data) reach the finish line they will all arrive at slightly different times...
Now in a 100m race the distance is relatively short and it does not give the data enough opportunity to skew too far apart.  This is the equivalent to a short parallel cable within which the data does not have the opportunity to skew.

If we increase the data of a race, for example from 100m to a marathon (26miles), now the time of arrival between the runners (data) will have massive differences between them!
IMPORTANT -  It is important to realise the difference between the running analogy and actual parallel cables.

In the running scenario, it is the physical properties of the runner that affects the finishing speed of the runners (data)

In a parallel cable it is the physical properties of each cable that affects the arrival time of the data.

Crosstalk

Another disadvantage of parallel transmission is cross-talk.  With Parallel transmission the wires are often very close to each other,  sometimes there can be electrical interference between the wires, this is known as "Cross-Talk".  This issue can cause errors in the data meaning that it will have to be re-sent.

Data Ribbons

One example of cables that use parallel transmission is data ribbons or parallel ATA Cables.

These are used over small distances, inside the computer to connect different pieces of hardware i.e. optical drives.

Depending on the size, 8, 16 or 32 bits can be transmitted simultaneously.
Direction of Transmission
Now that we know about the two types of transmission (Serial and Parallel) we need to consider the direction in which data can travel.

There are three main terms that describe which way data can travel, these are:

Simplex
Half Duplex
Full Duplex

Each of these have a set of rules that dictate the direction in which data is transmitted.  They can also be used in conjunction with Serial or Parallel transmission i.e. Serial Duplex.
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​Simplex Transmission​

​Simplex transmission allows for data to be sent in only one direction.

Example use: sending data from the keyboard to the CPU

​​Half Duplex

Half Duplex transmission allows data to travel in both directions, however, it cannot occur simultaneously.  This means that data can only travel one way at a time.

Example use:  Walkie talkies only allow communication one way at a time

​Full Duplex

Full Duplex allows data to travel in both directions simultaneously, it uses two cables to achieve this.

Example use: Internet cables that allow download and upload.