$2)$ In sliding$-$window flow control of a window size $50,$ the maximum

line utilisation for this link could be up to:

$($a$)1\%$

$2$

$($a$)$

$($b$)100\%$

$($b$)$

$($c$)99\%$

$($c$)$

$($d$)50\%$

$($d$)$

$3)$ A communication link uses stop$-$and$-$wait ARQ error control

protocol, the bit error rate $($BER$)$ is assumed to be BER$=10-12$ and

the frames are assumed to be $1000$ bits long.

The probability of receiving a frame in error is:

$($a$)10-10$

$($b$)10-9$

$($c$)103($d$)10-3$

$3\mathrm{.}1$

$($a$)$

$($b$)$

$($c$)$

$($d$)$

The probability that a frame is received successfully without

retransmission is approximately:

$($a$)0\mathrm{.}1$

$($b$)0\mathrm{.}998($c$)1$

$($d$)1000$x$10-10$

$3\mathrm{.}2$

$($a$)$

$($b$)$

$($c$)$

$($d$)$

The probability that it takes exactly $10$ attempts to transmit a frame

successfully is:

$($a$)10-18-10-27($b$)10-18($c$)10-12($d$)10$

$3\mathrm{.}3$

$($a$)$

$($b

$($C$)$

$($d$)$