Question

If originally RTT_S = 16 ms with α = 0.125 and β = 0.25.
Calculate the new RTT_S after the following events (times are relative to event 1)

Event 1:	00 ms	Segment 1 was sent	RTTS =  ms
Event 2:	10 ms	Segment 2 was sent	RTTS =  ms
Event 3:	16 ms	Segment 1 timed out and resent	RTTS =  ms
Event 4:	21 ms	Segment 1 was acknowledged	RTTS =  ms
Event 5:	34 ms	Segment 2 was acknowledged	RTTS =  ms

Answer 1

Inirial RTT (Original RTT)=16ms

Alpha (Smoothing Factor)=0.125

Beta (Deviation Factor)=0.25

Here we have to find out the the RTT (Round Trip time) after all the events (after segment 2 is acknowledged)

Since the question didn't asked for Time out timer so we don't need to calculate Deviation Factor (Usually caculated through Jacobson Algorighm) so we don't need beta value here.

Segment 1 is sent at 0ms and acknowledged at 21ms means Actual RTT of Segment 1 is 21ms and initial RTT was 16ms. So after recieving Segment 1 the next updated RTT will be

RTT1 (updated RTT after acknowleding segment1 ) = (Alpha)* ( Initial RTT) + (1-Alpha)*(Acutal RTT for segment 1)

RTT1 = (0.125)*(16)+(0.875)*(21)

RTT1 = 20.375

Now for the next RTT we will use RTT1

The next segment was being sent at 10ms and acknowledged at 34ms means Actual RTT of Segment 2 is 24ms and the RTT1 was 20.375. So the RTT after recieving Ack for segment 2 will be :

RTT2 (updated RTt after acknowleding Segment2 )=(Alpha)*(RTT1)+(1-Alpha)*(Actual RTT for segment2)

RTT2 =(0.125)*(20.375)+(0.875)*(24)

RTT2= 23.546875

So here is the Final RTT after all the events is RTT2=23.546875