Test Series

Question

Suppose host A is sending a large file to host B over a TCP connection. The two end hosts are 10msec apart connected by a 1Gbps link. Assume that they are using a packet size of 1000 bytes to transmit the file. Also assume for simplicity that ACK packets are extremely small and can be ignored. At least how big (in packets) would the window size have to be for the channel utilization to be greater than 80%? __________

Comments

Given answer is 2000 but I think ans. should be 2001. What is the actual ans?

Answer 1

Propogation Delay (T_Prop) = 10 * 10^-3 seconds

Bandwidth (R) = 10⁹ bps

packet size (L) = 1000 * 8 = 8000 bits

Transmit Time (T_Trans) = $\frac{L}{R}$ =  $\frac{8000}{10^9}$ = 0.008 * 10^-3 seconds

$Utilization = \frac{T_{Trans} * L}{T_{Trans} + 2 * T_{Prop}}$

$0.8 < \frac{0.008 * 10^{^{-3}} * L}{ 0.008 * 10^{-3} + 20 * 10^{-3}}$

$L > \frac{20.008 * 0.8}{0.008} = 2000.8$ Packets

So L should be 2001 Packets.

Answer 2

it's 2000

Comments

How???