辅导案例-1COMP 5416

  • May 15, 2020

1COMP 5416 Assignment 1 (2019)Due: 7/Sep/2019 23:59Question 1 (Delay). As shown in the figure below, a file of size F = 1000 bytes is transmitted on an end-to-end connectionover three links. Each link is 100 km. The signal prorogation speed is 2×108 m/s. Assume that a header of 40 bytes is added toeach packet. The bandwidth of all links is R = 1 Mbps at the beginning. The nodes use the store-and-forward scheme. (Ignoreprocessing delays at each node.)(1) How long does it take to transmit the file if the whole file is transmitted as a single packet.Now assume that the bandwidth of link B − C becomes 0.5 Mbps. Answer (2)–(4).(2) Repeat (1).(3) We would like to break the file into smaller packets to decrease the overall delay in the store-and-forward scheme. Assumethat each time you break the file to make a new packet, you have to add 40 bytes as the header of the new packet. Repeat (2)when we break the file into N = 4 packets.(4) What should be the optimal size of the packets to have the minimum overall delay to deliver the whole file? Find the overalldelay.Hint: Since the link B − C has a smaller bandwidth compared with A−B, packets could be queued for some time!$ % & ‘2Question 2 (Network Construction). Suppose that we have a network as shown in (a). Each link (A1A2, A2A3, B1B2, B2B3,C1C2, and C2C3) has a bandwidth of 10 Mbps. Obviously, this network is disconnected (e.g., A1 cannot connect to B3). We wantto make the network fully connected, and we have two approaches to expand the network, as shown in (b) and (c) respectively.In (b), each added link has a bandwidth of x Mbps. In (c), each added link has a bandwidth of y Mbps. We want to analyzethe performance of two approaches by analyzing their max min fairness. We have 9 flows sharing the network, starting at A1,B1, and C1 and ending at A3, B3, and C3 respectively. Their routes in (b) and (c) are shown in the table below.!” #” $”!%!&#%#&$%$&!” #” $”!%!&#%#&$%$&!! !!!” #” $”!%!&#%#&$%$&” “‘() ‘*) ‘+)Flows Starting and ending nodes Flow routes in (b) Flow routes in (c)1 A1, A3 A1 −A2 −A3 A1 −A2 −A32 A1, B3 A1 −B2 −B3 A1 −A2 −B2 −B33 A1, C3 A1 −B2 − C3 A1 −A2 −B2 − C2 − C34 B1, A3 B1 −B2 −A3 B1 −B2 −A2 −A35 B1, B3 B1 −B2 −B3 B1 −B2 −B36 B1, C3 B1 −B2 − C3 B1 −B2 − C2 − C37 C1, A3 C1 −B2 −A3 C1 − C2 −B2 −A2 −A38 C1, B3 C1 −B2 −B3 C1 − C2 −B2 −B39 C1, C3 C1 − C2 − C3 C1 − C2 − C3(1) Suppose x = 10 in (b), what are the data rates of the 9 flows if max min fairness is achieved.(2) Suppose y = 10 in (c), what are the data rates of the 9 flows if max min fairness is achieved.(3) For (b) and (c), draw figures to show how data rates of the 9 flows change with respect to x or y, if max min fairness is achieved.(4) From (3), discuss which solution, i.e., (b) or (c), is better? Why?3Question 3 (Wireshark). In this task, you will run a Wireshark experiment. Please follow the following procedure and answerquestions.1) Open a web browser. Clear the cache of the browser.2) Start up the capture of Wireshark packet sniffer.3) Enter the following URL into your browser.http://ec2-13-239-134-4.ap-southeast-2.compute.amazonaws.com/A1.html4) Your browser should display text and an image.5) When the image is completely loaded, enter the following URL into your browserhttp://ec2-13-239-134-4.ap-southeast-2.compute.amazonaws.com/A2.html6) When the image is completely loaded, refresh your browser (e.g., press F5).7) When the image is completely loaded, stop Wireshark packet capture.Questions(0) What is the time (date, hour, and minute) that you capture the packets? You will get 0 mark in Question 3 if you do notprovide the time.(1) What is the IP address of the server that sends you the base web page?(2) What is the IP address of the server that sends you the image?(3) Is non-persistent HTTP or persistent HTTP employed? Why?(4) What is the size of the image. How do you know that? You can only use the information provided by Wireshark capture.(5) In step 3), your browser has downloaded the image for the first time. This image may or may not be re-downloaded againin the following steps. In step 5), did you browser send the request for the image? If so, did the server send back the image toyour browser again? In step 6), did you browser send the request for the image? If so, did the server send back the image toyour browser again? (To answer these two questions, you should give screen-shots.)(6) Now you need to have a close investigation of the image you have downloaded (when you download the image for the firsttime). Locate the first four bytes of the image (.jpg file) in Wireshark. Screenshot the packet and location of the first four bytesshown by Wireshark. Locate the last four bytes of the image (.jpg file) in Wireshark. Screenshot the packet and location of thelast four bytes shown in Wireshark.To help you locate the bytes, you may consider to convert the original .jpg file into a byte-stream format. You may use thefollowing website https://www.onlinehexeditor.com/ to do so.(7) Following (6), which one of the following statements is correct. Give your screenshots to justify your answer.(a) The image is downloaded by a single packet.(b) The image is downloaded by multiple packets and the last packet includes HTTP response (200 OK) and the last portion ofthe image.(c) The image is downloaded by multiple packets. The last packet includes the last portion of the image. Then, an HTTP response(200 OK) is received in a separate packet.4Question 4 (Socket Programming for Blackbox Probing). In this question, you are required to build a UDP client to test thepropagation delay and link bandwidth (capacity) of a black box shown in the figure below. The black box emulates an uplink,a downlink, and a server. You need to build a UDP client using Python 3, to connect to the server using hostnameec2-13-239-134-4.ap-southeast-2.compute.amazonaws.comand port number 12004. You client should be able to send a message to the server and receive a response message from theserver. The length of your message is limited to 100 characters.(0) What is the time (date, hour, and minute) that you complete this question? You will get 0 mark in Question 4 if you do notprovide the time.(1) Send your student number (as a string encoded by utf-8) to the server and find the response message from the server.(2) Use Wireshark to capture the response packet. Screenshot the packet.(3) In the blackbox, suppose that the uplink and downlink have the same bandwidth (capacity). The propagation delays of theuplink and the downlink are the same. Only transmission delays and propagation delays are considered. All other delays inthe system can be ignored (e.g., queueing and processing delays). Revise your client to obtain the propagation delay and linkbandwidth of the uplink/downlink. We assume that each packet (sent/received) has a header of 28 bytes. (Hint: You can probethe overall delay from sending a packet to receiving the response.)ůĂĐŬŽdž;ŵƵůĂƚŽƌͿzŽƵƌĐůŝĞŶƚ ^ĞƌǀĞƌhƉůŝŶŬŽǁŶůŝŶŬ5Question 5 (DNS). Consider the network shown below. In the figure, DNSA is A’s local and AA DNS server and DNSB isB’s local and AA DNS server. TLD is the TLD DNS server of .com. Assume that the one-way propagation delay through eachnetwork (shown as clouds in the figure) is labled in the figure. The cached resource records at each host are listed in the tablebelow. “.” means the root DNS server.1 ms3 ms 5 ms10 ms50 ms1 msADNSADNSBBTLDRootHost name and/or IP address Cached recordsRoot 60.60.60.60 (.com, dns.com, NS)(dns.com, 121.121.121.1, A)TLD for .com 121.121.121.1 (sydney.com, dns.sydney.com, NS)(dns.sydney.com, 220.220.220.1, A)(comp5416.com, dns.comp5416.com, NS)(dns.comp5416.com, 111.111.111.1, A)DNSA for .sydney.com dns.sydney.com220.220.220.1(., dns., NS)(dns., 60.60.60.60, A)(.com, dns.com, NS)(dns.com, 121.121.121.1, A)(student.sydney.com, 220.220.220.220, A)DNSB for .comp5416.com111.111.111.1dns.comp5416.com(sydney.com, dns.sydney.com, NS)(dns.sydney.com, 220.220.220.1, A)(.com, dns.com, NS)(dns.com, 121.121.121.1, A)(., dns., NS)(dns., 60.60.60.60, A)(semester2019.comp5416.com, 111.111.111.111, A)A student.sydney.com220.220.220.220NoneB semester2019.comp5416.com111.111.111.111None(1) How long does host A take to resolve the IP address of host B when address resolution is done iteratively? Why?(2) How long does host B take to resolve the IP address of host A when address resolution is done iteratively? Why?Hint: You may not need to visit a DNS server as long as the requested information is already available.

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