Question

Question 1.) An ISP guarantees a minimum 102 kbps download speed. What should be the minimum TCP window size in bytes for a user who is downloading a large file through a link with with 28 ms round trip time? Assume that this network has a MSS of 512 bytes. Question 2.) Now this TCP connection is suddenly routed through a 204 ms delay link. For example the connection may have been using a terrestrial link before, but now use a satellite connection. What is the minimum window size now required to achieve the guaranteed throughput. Round up your answer to the nearest byte. Question 3.) Assume that there is capacity available in the network for the TCP connection to increase the throughput to the value guaranteed by the ISP. How long will it take for the TCP connection to increase the throughput to the desired level. Assume that there will not be any packet losses during the throughput increase and the connection has already gone past the stow start phase. Express your answer in seconds to two decimal places.

Answer 1

Q.1 Solution

RTT=28 ms

min bandwidth =throughput= 102 kbps= 102*1000

throughput= 1 window/RTT

window size= throughput * RTT

=102 *1000 *28/1000 bits

=102*28/8 bytes

=357 bytes