GATE CS 2014 Set 1 Q27 — Transport Layer: Flow Control, Congestion Control, UDP, TCP, Sockets

When a TCP timeout occurs, the congestion control parameters are updated as follows:

• The slow start threshold ($ssthresh$) is set to half of the current congestion window size:
  $$ssthresh = \frac{32\text{ KB}}{2} = 16\text{ KB} = 8\text{ MSS}$$
• The congestion window ($cwnd$) is reset to $1\text{ MSS} = 2\text{ KB}$.

Now, we trace the growth of $cwnd$ over successive Round Trip Times (RTTs):

1. Slow Start Phase (exponential growth until $cwnd$ reaches $ssthresh = 8\text{ MSS}$):
   • Initially (at $0$ RTT): $cwnd = 1\text{ MSS}$
   • After $1$ RTT: $cwnd = 2\text{ MSS}$
   • After $2$ RTT: $cwnd = 4\text{ MSS}$
   • After $3$ RTT: $cwnd = 8\text{ MSS}$ (reaches $ssthresh$)
2. Congestion Avoidance Phase (additive growth of $1\text{ MSS}$ per RTT):
   • After $4$ RTT: $cwnd = 9\text{ MSS}$
   • After $5$ RTT: $cwnd = 10\text{ MSS}$
   • $\dots$
   • After $n$ RTT: $cwnd = 8 + (n - 3)\text{ MSS}$

To reach the target congestion window of $32\text{ KB}$ ($16\text{ MSS}$):

Given that $1\text{ RTT} = 100\text{ msec}$, the total time taken is: