Question

1. Calculate the size of the TCP congestion window (in Maximum Segment Sizes) after the following events. Use TCP Slow Start, TCP Congestion Avoidance and TCP Fast Recovery as described in class and the book. The slow start threshold (ssthresh) is 8 MSS and the congestion windows is 1 MSS at the beginning of this scenario.

The sender receives -

3 new ACKs for data as expected, no duplicated ACKs

Timeout

6 new ACKs for data as expected, no duplicated ACKs

Event (ACK #, for example)	Window Size	ssthresh
ACK 1
ACK 2
ACK 3
Timeout
ACK 4
ACK 5
ACK 6
ACK 7
ACK 8
ACK 9

Answer 1

ACK 1   Window size = 1 MSS   ssthresh = 8 MSS
ACK 2   Window size = 2 MSS   ssthresh = 8 MSS
ACK 3   Window size = 4 MSS   ssthresh = 8 MSS
Timeout   Window size = 1 MSS   ssthresh = 4 MSS
ACK 4   Window size = 1 MSS   ssthresh = 4 MSS
ACK 5   Window size = 2 MSS   ssthresh = 4 MSS
ACK 6   Window size = 4 MSS   ssthresh = 4 MSS
ACK 7   Window size = 5 MSS   ssthresh = 4 MSS
ACK 8   Window size = 6 MSS   ssthresh = 4 MSS
ACK 9   Window size = 7 MSS   ssthresh = 4 MSS