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Consider an instance of TCP’s Additive Increase Multiplicative Decrease (AIMD) algorithm where the window size at the start of slow start phase is 1 MSS and the threshold at the start is 1st transmission is 16 MSS. Assume TCP use over a lossy link i.e., timeout occur after transmission of 7th packet . What is the congestion window size at the end of 14 RTT (in MSS)?
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At:

t=1,⇒1MSS

t=2,⇒2MSS

t=3,⇒4MSS

t=4,⇒8MSS

t=5,⇒16MSS

t=6,⇒17MSS  (Additive increase)

t=7,⇒18MSS  (fails)

New threshold ==> 18/2 = 9MSS

t=8,⇒1MSS

t=9,⇒2MSS

t=10,⇒4MSS

t=11,⇒8MSS

t=12,⇒9MSS

t=13,⇒10MSS

t=14,⇒11MSS

So, at the end of 14th sucessful transmission ,

The the congestion window size will be (11+1)=12MSS.

4 Comments

As per question, Timeout occured at 7th packet not 7th transmission.
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why did you add 1 at the end? 11+1?
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at the end of the 14th transmission, window size will increase by 1 for 15th transmission.
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 @akash.dinkar12 @balchandar reddy san @Sandy Sharma 

sir, timeout occurs after 7th pkt na? 

at rtt=4, we are sending 8 pkts right? then how is the solution correct? 

should the quesntion say-"timeout after rtt=7?" or both things mean same?

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