1. Synchronous - Asynchronous Data Transmission

2. Asynchronous ► The sender and receiver are not Synchronised. ► The sender sends only one character at a time.

3. Asynchronous ► Each character needs a start bit and a stop bit. ► There can be idle time between each character.

4. Asynchronous ► It is a slow and inefficient method of data transmission. ► It is an inexpensive method for low speed transmission.

5. Synchronous

6. Synchronous ► The senders and the receivers clocks are synchronised. ► The sender sends a packet of data at a time. ► Synchronisation is achieved by sending a ‘start’ frame and a ‘stop’ frame.

7. Synchronous ► It is a more efficient method of transmission as only a start and stop frame are required with up to 8Kb of data in the packet of data. ► Asynchronous has a much higher overhead. StopData up to 8 KbStart FrameFrame

8. Parity Check ► Used in Asynchronous transmission. ► Detects any errors in each character being sent.

9. Parity Check ► A bit in each byte is set aside as the parity bit. ► In even parity, the bit is set to 1 or 0 to ensure an even number of 1’s. ► In odd parity, the bit is set to 1 or 0 to ensure and odd number of 1’s. ► The receiving system checks the system being used and the number of 1’s

10. Checksum ► Used in Asynchronous Transmission. ► Checks errors in each packet of Data being sent.

11. Checksum ► The checksum is generate by treating all the bytes in the transmission as a number. ► It adds up all the bytes in the block. ► The checksum is attached to the block and transmitted along with the data. ► The receiver does the same calculation and if the checksums are the same the data was transmitted correctly, if not it’s re-sent.

12. Cyclic Redundancy Check ► The difference here is that the block of data is treated as one (very large) binary number. ► This is then divided by an Integer agreed between the sender and receiver. ► The Remainder only from the calculation is sent along with the data. ► The receiver can perform the same calculation and request re-transmission if there is a discrepancy.