Network/Info Assurance  Assignment Please show your working (if any) 1

Network/Info Assurance  Assignment

Please show your working (if any)

1.     [Transport Service Requirement] Why do HTTP, FTP, SMTP, and POP3 run on top of TCP rather than on UDP?

2.     [Email] Suppose Alice, with a Web-based e-mail account (such as Hotmail or gmail), sends a message to Bob, who accesses his mail from his mail server. Discuss how the message gets from Alice’s host to Bob’s host. When a user deletes an email on her client, what are the differences of emails on the server between POP3 and IMAP?

3.     [DNS] Describe two approaches to reduce the query overhead on DNS resolver.

4.     [Socket] What is a socket? Suppose a process in Host C has a UDP socket with port number 6789. Suppose both Host A and Host B send a UDP segment to Host C with destination port number 6789. Will both 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?

5.     [Demultiplex] Define multiplexing and demultiplexing. Briefly explain how TCP demultiplexing works.

6.     [rdt] Consider a reliable data transfer protocol that uses only negative acknowledgments. Suppose the sender sends data only infrequently. Would a NAK-only protocol be preferable to a protocol that uses ACKs? Why? Now suppose the sender has a lot of data to send and the end-to-end connection experiences few losses. In this second case, would a NAK-only protocol be preferable to a protocol that uses ACKs? Why?

7.     [Pipeline Protocols] Explain the differences of ACKs in Go-back-N and Selective Repeat pipeline protocols. For selective repeat protocol, given the sequence number range [0, s-1], what is the limits of window size N? Under the same setting, do we have a window size limits in Go-back-N protocol? Why?

8.     [TCP] What is a 3-way handshake in TCP/IP? Why do we need a 3-way handshake, why not just use a 2-way handshake?

9.     [TCP flow control] What is the TCP flow-control service and why is it important?

10.  [TCP congestion control] Why do we need congestion control? How does TCP handle congestion? Explain TCP’s slow start process.