TCP throughput – Consider that a single TCP (Reno) connection uses one 15 Mbps l
ID: 3593617 • Letter: T
Question
TCP throughput – Consider that a single TCP (Reno) connection uses one 15 Mbps link which does not buffer any data. Suppose that this link is the only congested link between the sending and the receiving hosts. Assume that the TCP sender has a huge file to send to the receiver, and the receiver’s receive buffer is much larger than the congestion window. We also make the following assumptions: each TCP segment size is 1,500 bytes; the two-way propagation delay of this connection is 150 msec; and this TCP connection is always in congestion avoidance phase, that is, ignore slow start.
a) What is the maximum window size (in segments) that this TCP connection can achieve?
b) What is the average window size (in segments) and average throughput (in bps) of this TCP connection?
c) How long would it take for this TCP connection to reach its maximum window again after recovering from a packet loss?
d) Repeat (a), (b), (c) but replacing the 15 Mbps link with a 15 Gbps link. Do you see a problem for the TCP connection in this scenario? Suggest a simple solution to this problem.
Explanation / Answer
What is the maximum window size (in segments) that this TCP connection can achieve?
Answer:
W*1500/RTT = 15M/8 =>
W = 83.3 segments (take the ceiling: 84)
2) What is the average window size (in segments) and average throughput (in bps) of this TCP connection?
Answer:
Because the connection always works under congestion avoidance, Average window size = 83*0.75 = 63 segments;
( 0.75W = average of (W/2+W))
Average throughput = 15M * 0.75 = 7.5MB.
3) How long would it take for this TCP connection to reach its maximum window again after recovering from a packet loss?
Answer:
About 84/2 RTT, or precisely 42 RTT = 4.2sec
4)Repeat (a), (b), (c) but replacing the 15 Mbps link with a 15 Gbps link. Do you see a problem for the TCP connection in this scenario? Suggest a simple solution to this problem.
1)8333 segments
2) 6250 segments and 75Mbps
3) 4167 sec
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