Computer Networks: Homework #13

Question 1

Consider a TCP connection between Host A and Host B. Suppose that the TCP segments traveling from Host A to Host B have source port number x and destination port number y. What are the source and destination port numbers for the segments traveling from Host B to Host A?

Answer 1

Source port number y and destination port number x.

Question 2

Describe why an application developer might choose to run an application over UDP rather than TCP.

Answer 2

An application developer may not want its application to use TCP’s congestion control, which can throttle the application’s sending rate at times of congestion. Often, designers of IP telephony and IP videoconference applications choose to run their applications over UDP because they want to avoid TCP’s congestion control. Also, some applications do not need the reliable data transfer provided by TCP

Question 3

Why is it that voice and video traffic is often sent over TCP rather than UDP in today’s Internet?

Answer 3

Today’s voice and video-traffic uses TCP to get through the firewalls that control the data traffic of modern end-systems, as some firewalls block data sent through UDP

Question 4

Suppose a process in Host C has a UDP socket with port number 6789. Suppose both Host A and Host B each send a UDP segment to Host C with destination port number 6789. Will both of these segments be directed to the same socket at Host C? If so, how will the process at Host C know that these two segments originated from two different hosts?

Answer 4

Yes, both segments will be directed to the same socket. For each received segment, at the socket interface, the operating system will provide the
process with the IP addresses to determine the origins of the individual segments.