Interview Q&A / Computer Networks

1. How do TCP slow start and congestion avoidance work? Trace cwnd over time.

   Slow start doubles the congestion window every round trip from a small start until it reaches a threshold (ssthresh). After that, congestion avoidance grows it by about one segment per round trip. On a timeout, ssthresh becomes half the window and cwnd restarts small.

   IntermediateQuick answer1 min read
2. What is the difference between TCP flow control and congestion control?

   Flow control stops a fast sender from overwhelming a slow receiver, using the receiver's advertised window. Congestion control stops senders from overwhelming the network in between, using a congestion window the sender maintains itself. The sender obeys the smaller of the two.

   IntermediateQuick answer1 min read