Question

6. (10 points) TCP Suppose a TCP Reno sender (congestion avoidance, fast retransmit, fast recovery) has an ssthresh 16 and a cwnd - 4. The sender has no outstanding unacknowledged segments and 240 more segments left to transmit. In addition, the receiver currently has an empty socket buffer that can hold up to 32 segments, and will continue to advertise a receiver advertised window that can hold 32 segments. Assume that there is no further loss of any segments or acknowledgements. a. (2 points) Excluding the TCP FIN handshake at the end of the transfer, how many more does it take for the transfer to finish? roundtrips b. (8 points) For each round-trip, show N, the number of segments transmitted by the sender during that particular round trip. R T T 2 1 3 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Answer 1

First Slow start phase operates till cwnd reaches ssthresh, Then with every successful transmission cwnd is incremented by 1 till cwnd becomes equal to the broadcasted window size by receiver which is 32.

ssthresh with every R1T, Gl Finstly simel cond doublad upto cwnd ssthresh -16- cond us Total seamonts tarans mihed 44 2+1628 2 RIT Cmd 48 16, fthis ilth every FTT nd imercases by 1tie reaches 32 advertined reeciw er cundo sink 12 RTT 4 24 2 5 23 2 1 2 L 20 aWnd Till here, 28t17t 48+ +24 +25 7 212 So20-217E23 segmenb tranfornd at RIT 13 23 segnenta cre Irourd Irips reireel13RTTs So no

If sufficient data is available then at RTT 13 also 26 bytes will be transferred. In the below table at RTT 13, 26 segments are sent as total segments to be transferred in question is 240.

segmants 3y dodo al seht Suffied data therr atsencder then is nel therr then ollorshyg happens 22 23 24 20 21 13 14 15 16 7 18 19 2 3 4 RTT 1 2 819 20 21 22 23 24 2523 27 28 24 20 3132 32 32 32 32 32 481617 As ecdwer aaoadcasts tronsmission forished 32 as its wmdow buffar sigt

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