4 / 18 TCP

Count The Duplicates

A sender transmits six 1000-byte segments back to back. The second one is dropped in the network. Every other segment arrives.

segment sent (seq) receiver's reaction
1000 ACK 2000
2000 dropped
3000 ACK 2000
4000 ACK 2000
5000 ACK 2000
6000 ACK 2000

The RTO has not expired. When does the sender retransmit, and what does it send?

A

Not until the RTO fires, since TCP has no negative acknowledgment

B

On the third duplicate, the fourth ACK 2000 overall, retransmitting seq 2000 only

C

On the third ACK 2000 overall, retransmitting seq 2000 only

D

On the third duplicate, retransmitting seq 2000 through 6000