(3x3 pts) Here is the FSM for CP from the book: new ACK new ACK duplicate ACK cw
ID: 3703194 • Letter: #
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(3x3 pts) Here is the FSM for CP from the book: new ACK new ACK duplicate ACK cwndMSS dupACKcount+ dupACkoount-o dupACKcount- transmit now segmentís), as allowed transmit now segmontís), as allowed cwnd-1 MSS ssthresh 64 KB cwnd 2 ssthresh Slow start avoidance timeout ssthresh-cwnd/2 cwnd-1 MSS dupACKcount-0 retransmit missing segment timeout ssthresh-cwnd/2 cwnd-1 MSS dupACKeount-o retransmit missing segment daplicate ACK dupACKcountt+ timeout new ACK ssthresh-cwnd/2 cwnd-8sthresh dupACKcount-o retransmit missing segment ssthresh-cwmd/2 cnd-ssthresh+3-MSS retransmit missing segment ssthresh-cwnd/2 retransmit missing segment Fast recovery duplicate ACK transmit new segmentis), as allowed Figure 3.52 FSM description of TCP congestion control We have been running for a while a. If we were just moved to slow start, what must have just happened? b. If we are in Congestion avoidance, and receive a triple-duplicate ACK, which event path # do we take? c. Whenever we arrive at Fast recovery from another state, what is the value of when we take the path to arrive there versus before we took the path?Explanation / Answer
a.
We can reach slow start in two way a) when protocal start but since it is given that protocol is running for a while hence this not possible.
So FSM can reach slow start from two state (i) congestion avoidence state and (ii) fast recovery state and both transition happens due to timeout i.e timer expire before acknowledgement receive.
b.
After receiving triple duplicate acknowledgement ssthresh value updated to half of congestion window(cwnd) and then congestion window(cwnd) set to new ssthresh + thrice of maximum segment size(MSS) and then retransmit missing segment and then transition to Fast recovery state
c
Before arriving at fast recovery the value of cwnd was equal to number of segment sent as well as acknowledged
but when we arrived at Fast recovery state then new congestion window is equal to half of congestion window at previous state plus thrice of maximum segment size
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