Question 3A.
[20 marks]
In this problem we consider the delay introduced by the TCP slow-start phase. Consider a
client and a Web server directly connected by one link of rate R/4. Suppose the client
wants to retrieve an object whose size is exactly equal to 14S, where S is the maximum
segment size (MSS). Denote the round-trip time between client and server as RTT
(assume to be constant). Ignoring protocol headers, determine the time to retrieve the
object (including TCP connection establishment) when 12 S/R > RTT > 4 S/R and RTT
≥ 12 S/R, respectively.
i) If 12 S/R > RTT > 4 S/R, the total delay is
$$2RTT + 4 S/R+ RTT +4 S/R+ RTT + 16S/R+28S/R=4RTT +52 S/R$$
ii) If RTT ≥ 12 S/R, the total delay is
$$2RTT + 4 S/R+ RTT +4 S/R+ RTT +4 S/R+ RTT + 28 S/R = 5RTT + 40 S/R$$
