COMMUNICATION NETWORKS

Answer the 4 question fully with all the details included (include all steps) Q1) Consider TCP slow start. Suppose a new TCP connection is just starting up, i.e. sends one maximum size segment (MSS) in the first transmission round. Suppose the Threshold is initially 20 MSS. Suppose the connection has infinite number of MSSs to send. Suppose that a time-out occurs at the end of transmission round 5. No other triple-duplicate ACKs or time-outs occur. a) Plot the Congestion Window (in units of MSS) as a function of time (in units of transmission rounds) for TCP Tahoe from transmission round 1 up to and including transmission round 14. Include the Threshold in your plot. b) Plot the Congestion Window (in units of MSS) as a function of time (in units of transmission rounds) for TCP Reno from transmission round 1 up to and including transmission round 14. Include the Threshold in your plot. 2) Suppose two hosts, A and B, are attached to opposite ends of a 1.5 Km cable, and that they each have one packet of 2000 bits (including all headers and preambles) to send to each other. Both hosts attempt to transmit at time t = 0. Suppose there are three hubs (repeaters) between A and B, each inserting a 30 bit delay. Assume the transmission rate is 10 Mbps, and CSMA/CD with backoff intervals of multiples 512 bits is used. After the first collision, A draws K= 0 and B draws K = 1 in the exponential backoff protocol. Ignore the jam signal. a) What is the one-way propagation delay (including repeater delays) between B and A in seconds. Assume that the signal propagation speed is 2 x 108 m/sec. b) At what time in seconds is B’s packet completely delivered at A. c) Now suppose that only B has a packet to send and that the repeaters are replaced with switches. Suppose that each switch has a 30 bit processing delay in addition to a store-and-forward delay. At what time in seconds is B’s packet delivered at A? 3) Consider the network shown in the figure below. Use Dijkstra’s shortcut path algorithm to compute the shortest paths from node w to all other network nodes. Show how the algorithm works by using the table format used in class. In the table please assign the nodes to the columns in alphabetical order, i.e., arrange the columns in the order t, u, v, x, and y from left to right. When you encounter ties in executing the algorithm, please break the ties in favor of the leftmost column. 4) Consider the network in Figure 3 consisting of a 100 Mbps Ethernet, an Ethernet switch (without cut-through switching functionality), and a 10 Mbps Ethernet. Suppose that A wants to send a large number of 5000 bit packets to B. (The 5000 bits include the data and all Ethernet header, trailer and preamble fields.) Suppose this is the only active session on the network. Assume propagation delays and processing times are negligible, and acknowledgments are instantaneously returned from B to A. a) Find the round-trip time, d. (Recall that the round-trip time is the length of time from when a host begins to transmit a packet until when the host receives an acknowledgment of the packet.) b) What is the maximum throughput in packet per second from A to B? c) Suppose A uses a pipelined transmission protocol with a window size of W = 1 packet. Find the throughput in packets/sec. d) Suppose the window size is W = 2 packets. Find the throughput in packets/sec.