$($a$)$ Describe the mathematical derivation of maximum throughput of Aloha.

$($b$)$ Describe Contention Window mechanism.

$($a$)$ Suppose there are five users A$,$ B$,$ C$,$ D and E$.$ They want to send $0,+1,+1,-1,-1$ bits,

respectively. Generate the code for each user and find the transmit sequence. Suppose that a user G

wants to decode the information sent from the user B$.$ How can he do this?

$($b$)$ Write down the working process of DNS with figure.

$($c$)$ Which persistence is best for reducing collision in a link?

How does recursive resolution differ from iterative resolution?

Describe the operation of CSMA$/$CA giving a flowchart.