2. Data Transmision Flashcards
What is Data Transmission?
Data transmission is the movement of data (bits) between at least two digital devices.
What is Packet Switching?
Packet Switching is the process when packets take on different routes over the network to avoid congestion and reach its final destination as soon as possible.
What do each packet contain?
Packet Header:
- IP address of the sender
- IP address of the receiver
- Sequence number
- Size of packets
Payload:
- Actual data being sent
Packet Trailer:
- Mechanism to identify the end of the packet and an error checking method
Pros and Cons of Packet Switching?
Pros:
- No single connection is fully occupying a communication line
- Busy or faulty lines will not stop data from reaching its destination
- Expansion is easy to achieve
Cons:
- Lost Packets will need to be resent
- Putting packets back into the correct sequence causes a small delay
What are the different types of transmission?
- Simplex
- Duplex
- Half Duplex
What is Simplex Transmission? and Examples
Simplex is one direction
- e.g. your keyboard to your CPU
What is Half - Duplex Transmission? and Examples
The transfer of data in both direction, one direction at a time.
- e.g. Printer cables
What is Full - Duplex Transmission? and Examples
The transfer of data in both directions at the same time.
- e.g. Telephones
What is Serial Transmission? and Examples
In serial data transmission, bits are sent sequentially (one after the other) down the same wire (channel).
- e.g. USB
What is Parallel Transmission? and Examples
In parallel data transmission, multiple bits are sent simultaneously down different wires (channels) within the same cable.
- e.g. Integrated circuits, inside computers
What is error checking?
When data is transmitted sometimes data can be corrupted during transmission.
Therfore To avoid these problems computers must check for errors.
What is parity Check? And its Method?
A method to check if errors exist using ODD or EVEN
- Before transmission, agreement made between sender and reciever
- They decide which parity wil be used ( 0 for even ) or ( 1 for odd )
- sending computeer sends data
- Recieving computer checks to make sure overall parity is agreed
- If the parity is incorrect, the recieving computer will request that the data is transmitted again.
What are the issues with Parity Check? And how to fix it?
If two bits are transposed (change places) then the computer could be fooled into thinking the data is correct and not corrupted. Therefore Parity blocks can be used.
What are Parity blocks?
They can check multiple bytes at the same time and have parity checks both vertically and horizontally using a parity byte
What is a checksum? And its method?
- A block of data sent alongside calculated checksum value
- Recieving computer calculates what it believes the checksum is
- Checksum compared to see if any errors have occured
- If checksum values dont match, recieving computer request for it to be resent.
