For this question, consider basic TCP protocol with Fast Recovery and Fast Retransmit. Current

congestion window is $4000$ bytes and each data segment TCP sends is exactly $500$ bytes, and we are in

Congestion Avoidance stage.

At time T$=0,$ Host A sends maximum allowed segments $(8$ segments with $500$ each$),$ while the second

segment happen to get lost in the transmission. This loss is then detected by the protocol$-$specific means

and the protocol invokes recovery actions. In the end, all data segments are correctly received by Host B$.$

Assume SRTT between host A and B is $1$ seconds and RTTdev$=0\mathrm{.}1$ sec$.$

$1\mathrm{.}1.$ TCP has $2$ mechanisms to detect loss: $3$ duplicate

ACKs and timeout. Which one host A can use to detect loss

of the $2$nd packet?