a) Why do UDP and TCP use a demultiplexing key for incoming packets that also include the source IP address and the source port number instead just of the (destination IP, destination port number) tuple ?

b) A TCP node receives a segment with data having sequence numbers from 1004 to 1100. The LastByteRead variable for that connection is 1200. Will the TCP layer deliver the data in the newly arrived segment to the process ? Explain.

c) Explain why a TCP segment timeout that is too short contributes to overall network congestion. What is the drawback of using a timeout value that is too long ?