$1$A$)$ Two neighboring 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:

a$)$ Before A sends any frames

b$)$ After A sends frames $0,1,2$ and receives acknowledgment from B for $0$ and $1$

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

d$)$ A fails to receive multiple RR form B$.$

$1$B$)$ Suppose a transmitter produces $50$ W of power.

a$)$ Express the transmit power in units of dBm and dBW $.$

b$)$ If the transmitter's power is applied to a unity gain antenna with a $900-MHz$ carrier frequency,

what is the received power in dBm at a free space distance of $100$ m $?$

c$.$ Repeat $($b$)$ for a distance of $10$ km $.$

$1$C$)$ Compute thermal noise level at the receiver's output for an effective noise temperature of $294$ K and

with $15$ MHz bandwidth. Given Boltzmann's constant $k=1\mathrm{.}3810-23\frac{J}{K}.$