Note: Problem numbers below refer to the 3rd edition of the text.. In all written assignmens, please show as muchof your work as you can. Even if you get a wrong answer, you can get partial credit if you show your work. If you make a mistake, it will also help the grader whow you where you made a mistake.

Problem 1.  In this problem we'll do some elementary calculations on transmission and propagation delay. Consider two hosts, A and B that are connected by a transmisison link of 1.4 Mbps. A packet length is (conveniently) 1.4 Kb (Kilobits). The length of the link is 100Km.

• What is the propagation delay from A to B - the amount of time from when the first bit of the packet is transmitted at A, until it is received at B?
• What is the transmission time of the packet at A ((the time from when the first bit of the packet is sent into the wire, and the time at which thelast bit is sent into the wire)
• Suppose now that that length of the link is doubled. What is the propagation delay from A to B now?
• Returning to the case that the distance between A and B is 100Km, how long must a packet be so that the receiver in receiving the first bit at the same time that the sender is sending the last bit?

Problem 2.  Chapter 1, Problem 8. However, rather than using the values given in the problem statement in the text, assume that each user needs 200Kbps, and that each user is active with probability 0.15. The link is a 1 Mbps link and there are 40 users in part c, as in the original problem statement. For parts b, c, and d, you can leave you answer in terms of an expression (e.g., with sums) to be evaluated (i.e., you need not provide a specific numerical value unless you want to).

Problem 3. Perform a traceroute(tracert) from a machine you have accress to and www.hamphigh.org (the public high school in Northampton MA) at threee different times of day.At each time of day, run tracert 5 times, which will gives you 15 measurement (3 eacht ime you run tracert)

• For each of the three times of day, give the 15 value fior the RTT delay from your machine to www.hamphigh.org. Calculate the average and standard deviation for each of the three times of day/
• How many routers are in the pacth at each time of day. Did the set of routers or the number of routers ever change?
• For one of your times of day tracert, list out the names of intervening routers. Based on these names, can you identify the ISPs in the path from source to destination. For example, my tracert to www.hamphigh.org shows a router name that ends in nox.org. If I doa little sleuthing and google on www.nox.org, I find out that nox.org is "Northern Crossraods" qhich appears to be a collaborative (that runs a network) of reesarch institutions in New England. There's no right or wring answer here - just see what you can find!
• Repeat the above three steps for www.lip6.fr, a site at the Univerity of Paris in France.

Problem 4. In this problem, we consider the performance of HTTP, comparing non-persisent HTTP with persistent HTTP. Suppose the page your browser wants to download is 10K bits longs, and contains 10 embedded images, each of 10K bits in length. The page and the 10 images are all stored onthe same server which has a 300 msec RTT from your browser. We will abstract the network path between your browser and the web server as a 100Mbps link. You can assume that the time it takes to transmit a GET message into the path is zero, but you should account for the time it takes to transmit the base file and the embedded objects into the "link." In your answer below, make sure to take into account the time needed to setup up a TCP connection (1 RTT).

• Assuming non-persistent HTTP (and assuming no parallel connections are open between the browser and server). How long is the response time - the from the when the user requests the URL to the point in time when the page and its embedded abjects are displayed? Make sure you describe the various components that contribute to this delay.
• Again assume non-persistent HTTP, but now assume that the browser can open as many parallel TCP connections to the server as it wants. What is the response time in this case?
• Now assume persistent HTTP (i.e., HTTP1.1). What is the response time, assuming no pipelining?
• Now suppose persistent HTTP withpipelining is used. What is the response time?

Problem 5. The purpose of this question  is just to give you a quick look at an Internet RFC (the technical standards for the Internet). You are not expected to read the RFC closely or in its entiety (of course you are welcome to do so, but this RFC is 176 pages long, and I am sure you have better ways of spending your time). Go to www.rfc-editor.org and download RFC 2616, which specifies HTTP 1.1. There is no need to print it out. Answer the following questions (which you can find inside the RFC).

• What is the purpose of the Accept-Language header field in HTTP1.1? Can multiple langiages be accepted? How does a browser specify its preference for a language to the server?