Consider the figure below, which plots the evolution of TCP\'s congestion window

Question

Consider the figure below, which plots the evolution of TCP's congestion window at the begining of each time unit (where the unit is equal to the RTT)

The initial value of cwnd is 1 and the initial value of ssthresh is 8.

Answer the following:

1. Give the range of times ( as Start Time - End Time ) at which TCP is in slow start: ______ , ______ , ______.

2. Give the range of times ( as Start Time - End Time ) at which TCP is in congestion avoidance: ______ , _____.

3. Give the time at which TCP is in fast recovery at the start of a time slot, when the flight of packets is sent: ____ , ____.

4. Give the times at which the first packet in the sent flight of packets is lost that was detected via timeout: ______.

5. Give the times at which the first packet in the sent flight of packets is lost that was detected via triple ducplicate ACKs: _______.

6. Give the times at which the value of ssthresh changes, and give the new value of ssthresh:

Changed at: _____ , new ssthresh at: _____.

Changed at: _____ , new ssthresh at: _____.

Explanation / Answer

1. Give the range of times ( as Start Time - End Time ) at which TCP is in slow start: __ 1-4__ , __21-24__ , __25-27__.

2. Give the range of times ( as Start Time - End Time ) at which TCP is in congestion avoidance: __4-12__ , __13-20__.

3. Give the time at which TCP is in fast recovery at the start of a time slot, when the flight of packets is sent: _12-13___ , __20-21___.

4. Give the times at which the first packet in the sent flight of packets is lost that was detected via timeout: _20_.

5. Give the times at which the first packet in the sent flight of packets is lost that was detected via triple ducplicate ACKs: __12__.

6. Give the times at which the value of ssthresh changes, and give the new value of ssthresh:

Changed at: __12___ , new ssthresh at: __8___.

Changed at: ___20__ , new ssthresh at: __9___.

Changed at: _24__ , new ssthresh at: __8___.

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