Hi,
"When both TCP congestion control and ECN are used, does TCP still go into fast recovery when a loss is detected by fast retransmit or it only goes into fast recovery when the ECE flag is received?"
Yes, fast recovery will be triggered either after fast re-transmit (triple dupack) or after ECN detection. Both mechanisms will be active.
"Is the multiplicative decrease in TCP Cubic 0.7 in both fast recovery and slow start?"
Fast recovery: new congestion window gets 0.7*old congestion window
After timeout: new slow start threshold gets 0.7*old congestion window but you go back to slow start (so the new congestion window goes back to the slow start inital value).
Ludovic
