Fast Retransmit and Recovery
Fast Retransmit: Received third duplicate ack:
- Set ssthresh to 1/2 of current cwnd
- Retransmit the missing segment
- Set cwnd to ssthresh+3
Fast Recovery: For each duplicate ack hence:
- Increment cwnd by 1 MSS
- New packets are transmitted once cwnd grows large enough.
- [If old cwnd was a pipe of length 1*RTT, the network gets a relief period of 1/2*RTT]