To implement packet re$-$transmissions in a window$-$based data transfer protocol $($with window$-$size

Ws $>1),$ the $$selective$-$repeat$$ policy $($SR$)$ incurs a higher software complexity than the $$goback$-$N$$

policy $($GBN$),$ because$2$

:

$($i$)$ Maximum allowed Ws in SR is only half of that in GBN;

$($ii$)$ SR treats each of Ws packets separately, but GBN treats the entire Ws packets as one unit;

$($iii$)$ SR reduces unnecessary packet retransmissions, when compared to GBN;

$($iv$)$ Retransmission timeout in SR is more sensitive to network transfer delays than in GBN$.$