HW 1, due Jan. 31, 2007 1. Consider a switch that is receiving packets of size L bits and forwarding them onto a link of transmission rate R bps that is M meters long. The propagation rate of the link is 3 x 10^8 meters/sec. The average arrival rate of packets is a pkts/sec. (a). Consider the graph of average queueing delay versus traffic intensity that we saw in lecture (Figure 1.14 of the book). Write a simple equation which roughly fits the curve in the graph. (b). Using the equation from part (b), how big should a be in terms of L and R before the average queueing delay is bigger than the transmission delay of the switch? (c). How big should M be in terms of L,R and a before the propagation delay is bigger than the avg. queueing delay and the transmission delay combined? (d). Assume the link is a fiber-optic cable under the Atlantic Ocean, so that its length is 5000 kilometers and its transmission rate is 100 Mbps. Assume a = 100 and L = 1000. Which delay will be greatest: average queueing, transmission or propagation? 2. Consider a circuit-switched phone network with 8 phones: A_1,..,A_4 and B_1,...,B_4. We want to allow any fourway simultaneous connection between the A's and B's. That is, each A is talking to a certain B and no two A's are talking to the same B. Assume each link in the network has capacity R bps. (a). Draw a network with as few links as you can that allows any fourway simultaneous connection with each connection transmitting at R bps. Use only switches that take 2 inputs and have 2 outputs. Explain. (b). Now assume the network from part (a) is packet-switched (for example, the eight hosts are communicating by skype) and that the switches use store-and-forward. Assume the packet size is L bits. Consider a given fourway connection. Assume each A sends out R/L pkts/sec to its corresponding B and the route that these packets take is the same as the circuit that that A and B would have used in part (a). Will there be any queueing delay at the routers? Why or why not? Assume each A sends just one packet. What will be the average arrival rate of bits at each B? 3. Log into an SMTP server (such as mail.sfu.ca) and try to send a mail message such that both the sender and recipient are not in the sfu.ca domain. Does it let you? Why or why not? Provide a transcript of the session. 4. When a previous user of www.amazon.com visits the website again, it usually tries to recommend books based on what the user has bought or searched for in the past. It uses cookies to identify the user. Would it be possible to use your knowledge of http and telnet to find out the recommendations of some other user (not a specific user, just any other user besides yourself)? How would you try to do it? What are the obstacles? 5. This is a programming question. We will briefly discuss the socket API in Java in the next lecture, but you can easily read about TCP sockets in sections 2.7 and 2.9 of the text. Program a very simple web browser which does the following: it is invoked on the command line with the command MyBrowser where is the URL of some html file. The browser opens a TCP connection to the appropriate server and gets the html file using http commands. It saves the html file as a file on the local host. You don't need to handle any exceptions. EXTRA CREDIT: Implement a "web archive" function, where the browser automatically gets all html files referenced by the original html file (but not the files referenced by those new files--i.e. just distance 1).