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Consider a source using TCP-Reno (fast-retransmit and fast-recovery mechanisms) to send data to a destination. It is given the RTT of the link is 800 ms and the sender’s window size is 8 segments. The sender sends segments at a regular rate of one every 100 ms, and the receiver sends ACKs back at the same rate without delay. A segment is lost, and the receiver sends 3 duplicate ACKs to trigger the fast-retransmit. If the sender waits for ACK of the retransmitted segment before advancing the window then the total time the sender lost (as compared to lossless transmission) is ________.
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Suppose pakcet number P is sent at t=0 by the sender. Suppose P is lost then  remaining 7 packets i.e P+1 to P+7  will be sent at t=100, 200, ..., 700, since the window size is 8.

Sender stops sending at t=800, since window size is 8 and ACK for P has not arrived. ACK for P+1, P+2 and P+3 will be duplicate ACKs and will arrive at t=900, 1000 and 1100. P is re-transmitted at t=1100. ACK arrives at 1900.

Time lost = 1900-800 = 1100.
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