1- We define propagation delay as the time taken by a bit to reach from a sender to a receiver. We define transmission delay as the amount of time required to transmit all of a packet's bits into the network. Given a sender and a receiver, we assume they communicate to each other, using the CSMA/CA protocol with RTS/CTS enabled. We assume the propagation delay of a packet from the sender to receiver is , each time slot in the contention window is , the transmission delay of RTS or CTS is 15, SIFS and DIFS are and 3, respectively.

a) If the sender has a data packet to send at time 0, and the random number (of slots) it chooses is 2, what is the earliest (possible) time it starts sending an RTS message?

b) Based on question 1.a), what would be the earliest time for the receiver to start sending a CTS message?

c) Based on question 1.b), if the transmission delay of the data packet is 100, what would be the earliest time for the receiver to start sending an acknowledgement packet?

d)Based on question 1.c), if the transmission delay of an acknowledgement packet is15, what would be the earliest time for another sender to start sending an RTS message?

2- Assume that you just got out of the airplane and you switched on your cell phone. If the closest BS is located at a distance of 5 kms, what is the minimum and the maximum delay before a contact is established between your cell phone and the nearest BS, given the BS transmits beacon signals every one second?

3- In the backbone network, it is desirable to find the shortest path from the source to the destination. How do you do this in a wireless network environment, where the subscribers do have finite mobility?

4- Given two prime numbers, p = 37 and q = 23 , define the private and public keys by selecting appropriate value of the number e?