Question: In the Reno TCP, when TCP enters the fast recovery, if duplicate ACKs continue to come, TCP ____________________________________.

Answer:

in Reno TCP, when TCP enters the fast recovery state, if duplicate ACKs continue to arrive, TCP stays in this state and the congestion window (cwnd) is increased exponentially. This is known as the fast retransmit mechanism.
When a sender receives three duplicate ACKs, it assumes that a packet has been lost and immediately retransmits the lost packet without waiting for a timeout. The sender then enters the fast recovery state and sets the cwnd to the value of the congestion window at the time of the loss.
If the sender receives an additional duplicate ACK while in the fast recovery state, it increases the cwnd by one for each duplicate ACK received, effectively growing the congestion window exponentially. This allows the sender to recover from the packet loss quickly, while also being conservative about the amount of traffic sent to avoid further congestion.
If the sender receives an ACK for the lost packet, it exits the fast recovery state and returns to the congestion avoidance phase. If no duplicate ACKs are received for a period of time equal to the Round Trip Time (RTT) of the connection, the sender assumes that the congestion has subsided and returns to the congestion avoidance phase.

MCQ: In the Reno TCP, when TCP enters the fast recovery, if duplicate ACKs continue to come, TCP ____________________________________.

A. stays in this state, but the cwnd grows additively
B. stays in this state, but the cwnd grows exponentially
C. moves to slow start state
D. moves to the congestion avoidance state but deflate the size of the cwnd to ssthresh value

Correct Answer: A. stays in this state, but the cwnd grows additively

in Reno TCP, when TCP enters the fast recovery state, if duplicate ACKs continue to arrive, TCP stays in this state and the congestion window (cwnd) is increased exponentially. This is known as the fast retransmit mechanism.
When a sender receives three duplicate ACKs, it assumes that a packet has been lost and immediately retransmits the lost packet without waiting for a timeout. The sender then enters the fast recovery state and sets the cwnd to the value of the congestion window at the time of the loss.
If the sender receives an additional duplicate ACK while in the fast recovery state, it increases the cwnd by one for each duplicate ACK received, effectively growing the congestion window exponentially. This allows the sender to recover from the packet loss quickly, while also being conservative about the amount of traffic sent to avoid further congestion.
If the sender receives an ACK for the lost packet, it exits the fast recovery state and returns to the congestion avoidance phase. If no duplicate ACKs are received for a period of time equal to the Round Trip Time (RTT) of the connection, the sender assumes that the congestion has subsided and returns to the congestion avoidance phase.