A$.$ Assume ten devices are arranged in a mesh topology. How many cables are needed? How many ports are needed for each device?

B$.$ What is the use of port address?

f$.$ Suppose a computer sends a packet at the network layer to another computer somewhere in the Internet. The logical destination address of the packet is corrupted. What happens to the packet?

D$.$ What is bit$-$stuffing?

E What are the advantages and disadvantages of reservation based multiple access?

A$.$ Two neighbouring nodes $($A and B$)$ use a sliding$-$window protocol with a $3-$bit sequence number. As the ARQ mechanism, Go$-$back$-$N is used with a window size of $4.$ Assuming $A$ is transmitting and $B$ is receiving, 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 $3,4,$ and $5$ and B acknowledges $4$ and the ACK is received by $A.$

B$.$ A channel has a data rate of $4kbps$ and a propagation delay of $20ms.$ For what range of frame sizes does stop$-$and$-$wait give an efficiency of at least $50\%?$

A$.$ Suppose that a Selective$-$repeat ARQ is used where window size $W=4.$ Show, by example, that what should be the maximum length of sequence number in bits.

B$.$ There are only three active stations in a slotted Aloha network: A$,$ B$,$ and C$.$ Each station generates a frame in a time slot with the corresponding probabilities $p_A=0\mathrm{.}2,p_B=0\mathrm{.}3,$ and $p_C=0\mathrm{.}4$ respectively.

$($a$)$ What is the throughput of each station?

$($b$)$ What is the throughput of the network?

$($c$)$ What would be the throughput of the network if pure Aloha is used?

$A_i$ Consider a CSMA$/$CD network with a data rate of $10Mbps,$ the minimum frame size is found to be $512$ bits for the correct operation of the collision detection process. What should the minimum frame size be if we keep the size of the network constant, but we increase the data rate to each of the following?

a$.100Mbps$

b$.1Gbps$

B$.$ Using a topology of four nodes, explain hidden and exposed terminal problems. Show that using RTS$-$CTS packet exchange, exposed terminal problem can not be resolved.