(a) Explain what asynchronous transmission is and give two advantages and two disadvantages of using this type of transmission.

(b) One of the goals of multiplexing is efficiency.

(i) Explain what is multiplexing and how does it improve system design.
(ii) Give any two applications of Frequency Division Multiplexing (FDM).
(iii) Ten signals, each requiring 4000 Hz are to be multiplexed together using

FDM. What is the minimum bandwidth of the link if there is a need for a guard band of 400 Hz between the channels to prevent interference?

(c) Explain the operation of the Stop and Wait flow control protocol and give one disadvantage of using this protocol.

(d)  Two adjacent nodes (A and B) use a  sliding window protocol  and a 3-bit sequence number. As the  ARQ  mechanism,  Go-Back-N  is used and the window size is 4. Assuming that  A transmits and B receives,  by using appropriate diagrams  and giving appropriate explanations,  show the window positions for the following succession of events:

(i) Before A sends any frames.

(ii) After A sends frames 0, 1, 2 and B acknowledges 0, 1 and the ACKs are received by A.

(iii) After A sends frames 3, 4, 5 and B acknowledges 4 and the ACK is received by A