TCP Packet Drop - Network Congestion

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The link's bandwidth are setup in a way that the sender will transmit faster than the router can forward. The buffer queue of the 2nd link is set to 5 packets.After sometime the sender will overflow the links buffer and the interface will start drop packets. The sender will retransmit the first packet because it receives duplicate ACKs. The 2nd retransmission happened around 0.66s because the timeout at the sender side was expired.