Homework 1. Theoretical questions PDF

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Homework 1. Theoretical questions
Homework 1. Theoretical questions
Homework 1. Theoretical questions
Homework 1. Theoretical questionsHomework 1. Theoretical questions...

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HOMEWORK 1 Due Date: Wednesday, Oct. 13 11:59 PM EST Submission: Upload PDF file to courseworks

1. Wireshark Lab: Complete the “Getting Started” Wireshark Lab at https://gaia.cs.umass.edu/kurose_ross/wireshark.htm . Answer the questions under “What to hand in” (you can provide a screenshot for question 4). 2. Protocols: Design and describe an application-layer protocol that allows a user to check for COVID-19 vaccination availability for kids 5-11 (we assume it is available now, FDA and Pfizer indicate it is a matter of weeks). The protocol takes basic user information (name, email address, age) and then returns one of four responses: (a) an available time slot; (b) an error if no appointment is available for the interval; (c) an indication that an email will be sent if a slot opens up (if the number of requests is just modestly larger than available doses); (d) an error if the querier is not eligible to be vaccinated at this time (e.g., because they are not in the 5-11 age range). Use the ladder diagram similar to Fig. 1.2 in the textbook. You do not have to indicate lower-layer errors such as packet loss or describe specific protocols such as TCP or HTTP (since we have not covered these in class). Describe the protocol message content. On the back-end, your system queries one or more "points of distribution", such as hospitals, clinics or city and state temporary vaccination sites. (See https://vaccinepod.nyc.gov/ for the NYC version.) 3. Packet loss: Consider a path with three routers, i.e., a total of four links, connecting a client to a server. Each link has a packet loss probability of p, and packet losses are independent. A. What is the probability that a packet sent by the client arrives at the server? B. If a packet is lost along the path, the client retransmits it. (Routers do not retransmit packets in our model.) How often, on average, will each packet be sent, given p? 4. Routes: So-called "looking glass" web sites provide remote access to traceroute and other tools. Traceroute is also installed on most desktop systems and allows you to trace the route taken by packets. Using http://www.cogentco.com/en/network/looking-glass, trace the route from three of their routers, each from a different country, to your home computer. You can find the

Internet (IPv4) address by using sites such as whatismyip (https://www.whatismyip.com/) . Reverse the trace from your computer, using the MacOS/Linux traceroute or Windows tracert tools, to the Cogent server listed first in each of the three traces. (Students located in China can also try https://ipms.chinatelecomglobal.com/public/lookglass/lookglassDisclaimer.html ) A. Record the output, i.e., six traces (three cities, back-and-forth), and the time and date of your experiment. B. Can you guess what cities the routes traverse? (You do need to use an IP-address-to- location lookup tool.)

C. Is the route to the Cogent server and back the same, by IP address or by city? D. Repeat the experiment (A) after at least a day. Did anything change? 5. File transfer: You need to urgently move a very large file of data from New York to Atlanta. You have a 1 Gb/s link available to you, via Internet2, or you can use a disk-based delivery like the Amazon Snowball appliance (https://aws.amazon.com/snowball/features/) using FedEx overnight delivery. The delay of overnight delivery depends on the service chosen; for simplicity, assume 12 hours (which would be their “first overnight” service). For what file sizes would you use Internet2 and when FedEx? Assume that the University pays for FedEx and Internet2, so cost is not a major concern. (Digital movies are distributed (https://www.cru-inc.com/industries/digital-cinema/) by disk to movie theaters.) 6. End-to-end delay: Using the ping command and the –s option (for Linux and MacOS; –l on Windows) to vary the packet size, measure the round-trip latency to a university web site, at least 2,000 km away from your current location (in order to make propagation delay meaningful). Measure at least 100 samples for each packet size; the number of different packet sizes is up to you and just needs to be sufficient to support your estimates. Be sure to discuss how you arrived at your results. ● Based on your measurements, estimate (e.g., the statistical average) the total end-to-end propagation, transmission and queueing delay. ● For queueing delay, give an estimate of mean and standard deviation. ● Compare the approximate geographical distance to the network-measured distance obtained via the propagation delay.

7. Voice: Consider sending voice, e.g., via Skype or Zoom or some home and enterprise phone systems, over a packet-switched network. This is known as voice-over-IP (VoIP). Each packet contains a short segment of audio and packet headers that allow the packet to be routed, recognized and processed. Assume that the packet header is 40 bytes long. The voice encoding generates a 64 kb/s stream of voice bits. Assume you want the voice segment to reach the destination within 200 ms. (One-way delays longer than 200 ms make conversation awkward.) How fast does your network have to be and how much voice data would you put in each packet? (We ignore the propagation delay here.) 8. Throughput: In the figure below, both A and C are sending data at the same time to host B. Compute the throughput A-B and C-B separately for the upper and lower figure, i.e., four answers. There may be multiple good answers, so justify how you arrived at your conclusion....