$15)$ In G$-$back$-$N$,$ if the window size is $100,$ the BER is $104$ and the

frame length is $1000$ bits, what will be the expected number of

transmissions of a frame?

$($a$)$

$0\mathrm{.}9$

$($b$)12\mathrm{.}11$

$($c$)1\mathrm{.}11$

$($d$)1\mathrm{.}2$

$15$

$($a$)$

$($b$)$

$($C$)$

$($d$)$

$16)$ In a communication network, a node A sends data to node B$,$

the channel between A and B has a data rate of $1000$ kbps and a

propagation delay of $10$ ms$.$ For what frame sizes does stop$-$and$-$

wait give an efficiency of $100\%?$

$($a$)$

$40$kbits

$($b$)100$ kbits $($c$)50$ kbits

$($d$)$ neither a$,$ b or c

$16$

$($a$)$

$($b$)$

$($c$)$

$($d$)$

$17)$ For the Selective Reject ARQ protocol, if the probability that it

will take exactly $3$ attempts to transmit a frame successfully is

$0\mathrm{.}125,$ the probability of receiving a frame correctly is given by:

$($a$)12\mathrm{.}5\%$

$($b$)0\mathrm{.}875$

$($c$)100\%($d$)$ neither a not b nor c

$17\mathrm{.}1$

$($a$)$

$($b$)$

$($c$)$

$($d$)$