Problem $3$

Consider that Alice and Bob communicate with each other using a transport protocol based on Go$-$Back$-$N $($GBN$).$ More particularly, they use the most basic version of GBN$.$ For every received data segment, the receiver answers with an ACK. The ACK number refers to the next expected in$-$order sequence number and cumulatively acknowledges all the previous data segments. Out$-$of$-$order packets are not saved in a buffer. There are no mechanisms in place to signal dropped or out$-$of$-$order packets. To recover from heavy packet losses a timeout value is used and data segments are retransmitted once the timeout is reached.

Answer the following true$/$false questions considering the above protocol. Check either true, false or nothing. For each question answered correctly, one point is added. For each question answered falsely, one point is removed. There is always one correct answer.

$\backslash$begin$\{$tabular$\}\{|$l$|$l$|$l$|\}$

$\backslash$hline True & False & $\backslash$multicolumn$\{1\}\{$c$|\}\{$ Statement $\}\backslash \backslash$

$\backslash$hline & & The protocol used by Alice and Bob is a sliding window protocol. $\backslash \backslash$

$\backslash$hline & & $\backslash$begin$\{$tabular$\}\{$l$\}$

Only the length of the timeout value influences the transmission duration $\backslash \backslash$

of a message.

$\backslash$end$\{$tabular$\}\backslash \backslash$

$\backslash$hline & & $\backslash$begin$\{$tabular$\}\{$l$\}$

A file can be successfully transmitted even if the number of ACKs $\backslash \backslash$

received by the sender is smaller than the number of transmitted data $\backslash \backslash$

segments.

$\backslash$end$\{$tabular$\}\backslash \backslash$

$\backslash$hline & & A dropped packet is the only possibility for duplicate ACKs at the sender $\backslash \backslash$

$\backslash$hline

$\backslash$end$\{$tabular$\}$