The document discusses the basic components of communication systems and data transmission methods. It explains that every communication system has 5 basic requirements: a data source, transmitter, transmission medium, receiver, and destination. It then describes serial and parallel transmission methods and how asynchronous transmission is the most common type of serial data transfer as it allows packet switching and bandwidth sharing. Finally, it discusses different network topologies like bus, ring, and star and compares their advantages and disadvantages.

1. Communications Systems

2. 5 Basic Components Communications Systems Every communication system has 5 basic requirements Data Source (where the data originates)

3. Transmitter (device used to transmit data)

4. Transmission Medium (cables or non cable)

5. Receiver (device used to receive data)

6. Destination (where the data will be placed)

9. Data is transmitted, on a single channel, one bit at a time one after another - Much faster than parallel because of way bits processed (e.g. USB and SATA drives) Serial Transmission Sender transmitted Receiver received 1 0 1 0 0 1 1 0

10. Receiver received each bit has it’s own piece of wire along which it travels - often used to send data to a printer Parallel Transmission Sender transmitted All bits are sent simultaneously 1 0 0 1 1 0 0 1

11. Why Not use Parallel Instead of serial? Due to inconsistencies on channels data arrives at different times

12. Because of the way it is transmitted packet switching cannot be used

13. The above two points makes parallel slower than serial and requires higher bandwidth.

14. Parallel transmissions are rarely used anymore

15. Synchronous Transmission all data sent at once and no packet switching Asynchronous Transmission Uses stop/ start bits

16. most common type of serial data transfer

17. Allows packet switching

18. Allows sharing of bandwidth (i.e. talk on phone while another person is using internet) Synchronous Vs Asynchronous Transmissions

19. Start and Stop Bits In the asynchronous method, each character is placed between start and stop bits ( framing ) Framing ASCII ‘A’ (41H) LSB MSB

20. Data Transfer Rate Rate of data transfer: bps (bits per second)