May 15, 2007 - Q1 â The TCP in station A sends a SYN segment with ISN = 1000 and MSS = 1000 to station B. Station B replies with a SYN segment with ISN ...
CSIS0234A Computer and Communication Networks Assignment Four (7%) Due date: 5:00pm May 15, 2007
Short Questions Please hand-in the written assignment to the course assignment box (B2). Q1 – The TCP in station A sends a SYN segment with ISN = 1000 and MSS = 1000 to station B. Station B replies with a SYN segment with ISN = 5000 and MSS = 500. Suppose station A has 10,000 bytes to transfer to B. Assume the link between stations A and B is 8 Mbps and the distance between them is 200 m. Neglect the header overheads to keep the arithmetic simple. Station B has 3000 bytes of buffer available to receive data from A. Sketch the sequence of TCP segment exchanges, including the necessary parameter values in the segment headers, and the state as a function of time at the two stations under the following situations: a) Station A sends its first data segment at t = 0. Station B has no data to send and sends an ACK segment every other frame. b) Station A sends its first data segment at t=0. Station B has 6000 bytes to send, and it sends its first data segment at t = 2 ms. Q2 – Consider the three-way handshake in TCP connection setup. (a) Suppose that an old SYN segment from station A arrives at station B, requesting a TCP connection. Explain how the three-way handshake procedure ensures that the connection is rejected. (b) Now suppose that an old SYN segment from station A arrives at station B, followed a bit later by an old ACK segment from A to a SYN segment from B. Is this connection request also rejected? Q3 a) Consider the effect of using slow start on a line with a 10-msec round-trip time and no congestion. The AdvertisedWindow is 24 KB and the maximum segment size is 2 KB. How long does it take before the first full window can be sent? b) What is the fastest line speed at which a host can blast out 1500-byte TCP payloads with a 120-sec maximum packet lifetime without having the sequence numbers wrap around? Take TCP, IP, and Ethernet header overhead into consideration. Assume that Ethernet frames may be sent continuously. Q4 – Consider the TCP state transition diagram, how many ways (combinations of transitions) are there to get a connection from the ESTABLISHED state to the CLOSED state? Explain each circumstance that results in a specific teardown sequence.
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(i) Consider the network topology depicted in the above figure where the boxes labeled with "?" are Ethernet hubs. 1. Does node A's ARP table ever contain entries for node B and node C network addresses? 2. When node A is sending a packet to node C, what Ethernet address does node A use for the destination? 3. Suppose there is two-way communication between nodes A and B. Does node C get to see this traffic? (ii) Assume that the boxes labeled with "?" are Ethernet switches. Answer the same subquestions from (i). (iii) Assume that the boxes labeled with "?" are IP routers. Answer the same sub-questions from (i). Q6 – Apply the Bellman-Ford’s and Dijkstra’s algorithms to find the shortest path from A to H for the below network. Show your steps. 2
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Q7 – Twelve stations (H1 – H12) are connected to an extended LAN through transparent bridges (B1, B2, B3, & B4), as shown in the figure below. Initially, the forwarding tables of all switches are empty. Suppose the following stations transmit frames: H5 transmits to H6, H7 transmits to H3, H6 transmits to H1, H2 transmits to H10, H4 transmits to H12, H11 transmits to H5, and H3 transmits to H4. Fill in the forwarding tables with appropriate entries after the frames have been completely transmitted.
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