Questions: (50 points)
1, (6 points) Suppose there are exactly two packet switches (switch#1 and switch#2) between a sending host and a receiving host. The transmission rate between the sending host and switch#1 is R1, 200Mbps. The transmissions rate between switch#1 and switch#2 and between switch#2 and the receiving host are R2, 400Mbps and R3, 500Mbps, respectively. Assuming that the switches use store–and–forward packet switching, what is the total end–to–end delay to send a packet of length L, 1000 bytes?
(Ignore queuing, propagation delay, and processing delay.)
2, (8 points)
(a) In general, how long does it take a packet of length L to be delivered from the sending host to the receiving host over a link of distance d, propagating speed s, and transmission rate R bps (consider both transmission delay and propagation delay)?
(b) How many milliseconds (ms) does it take for a packet of length 1,000 bytes to be delivered from the sending host to the receiving host over a link of distance 2,000 km, propagation speed 2.5x108 m/s, and transmission rate 50Mbps (consider both transmission delay and propagation delay)?
(c) How many milliseconds does it take for the first bit of the packet to arrive at the receiving host (start to count the time when the sending host starts to transmit the first bit of the packet)?
(d) How many milliseconds does it take for the whole packet to be put on the link (start to count the time when the sending host starts to transmit the first bit of the packet)?
3, (6 points) Suppose Host A wants to send a large file to Host B. The path from Host A to Host B has three links, of rate R1=100Mbps, R2=500Mbps, and R3=200Mbps.
(a) Assume no other traffic in the network, what is the throughput for the file transfer?
(b) Suppose the file is 500MB (Assume 1MB= 106 bytes). Dividing the file size by the throughput, roughly how long will it take to transfer the file to Host B?
4, (4 points) What information is used by a process running on one host to identify a process running on another remote host? For a communication between a pair of processes, which process is the client and which is the server?
5, (8 points) True or false? Why?
a, A user requests a Web page that consists of some text and two images. For this page, the client will send one request message and receive one response message.
b, Two distinct Web pages (for example, www.nova.edu/resources/current_students.html and www.nova.edu/resources/faculty_staff.html ) can be sent over the same persistent connection.
c, With persistent connections between browser and origin server, it is possible for a single TCP segment to carry two distinct HTTP request messages.
d, The Date: header in the HTTP response message indicates the time and date when the HTTP response was last modified.
6, (8 points) What is an application–layer message? A transport–layer segment? A network–layer datagram? A link–layer frame?
7, (2 points) 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 10408 and
destination port number 80. What are the source and destination port numbers for
segments traveling from Host B to Host A on the same TCP connection?
8, (4 points) Suppose a process in Host C has a UDP socket with port number 8880, Suppose Host A and Host B each sends a UDP segment to Host C with destination port number 8880. Will both of these two 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?
9, (4 points) Suppose that a Web server runs in Host C on port 80. Suppose this Web server uses persistent connections, and is currently receiving requests from two different Hosts, A and B. Are all of the HTTP requests from Host A and B being sent through the same socket at Host C? If they are being passing through different sockets, do both of the sockets have port 80? Discuss and explain.
Wireshark Lab: HTTP (30 points)
Wireshark Lab – HTTP: Answer question 1–15 in this lab. (Listed in another file named “Wireshark_HTTP_v8.0.pdf”). (2 points each)
For the Wireshark Lab questions, you should show me where you obtained your answers.
The following paragraph is taken from the Lab assignment:
“By looking at the information in the HTTP GET and response messages, answer the following questions. When answering the following questions, you should print out the GET and response messages (see the introductory Wireshark lab for an explanation of how to do this) and indicate where in the message you’ve found the information that answers the following questions. When you hand in your assignment, annotate the output so that it’s clear where in the output you’re getting the information for your answer (e.g., for our classes, we ask that students markup paper copies with a pen, or annotate electronic copies with text in a colored font).”
