Computer Networks. Homework #3: Due 11 November 2015 (Wednesday) Just before Midterm#2!

Transcription

1 Computer Networks Homework #3: Due 11 November 2015 (Wednesday) Just before Midterm#2! Problem #1. Assume you need to write and test a client-server application program on two hosts you have at home. a. What is the range of port numbers you would choose for the client program? b. What is the range of port numbers you would choose for the server program? c. Can the two port numbers be the same? Problem #2. In a network with fixed value for m > 1, we can either use the Go-Back-N or the Selective-Repeat protocol. a. Describe the advantage and the disadvantage of us each. b. What other network criteria should be considered to select either of these protocols?

2 Problem #3. Some of the application programs can use the services of two transport-layer protocols (UDP or TCP). When a packet arrives at the destination, how can the computer find which transport layer is involved? Problem #4. Assume a TCP server is expect to receive byte It receives a segment with the sequence number 6001 that carries 2000 bytes. a. If the server has bytes 4001 to 5000 to send, what should the reaction of the TCP server be to this event? b. Can you justify the reaction? Problem #5. A sender sends a series of packets to the same destination us 5-bit sequence numbers. If the sequence numbers start with 0, what is the sequence number of the 100th packet?

3 Problem #6. Colleegee off Infforrmaatti I ion aand Communiccaatti Given the FSMs for the Go-back-N protocol. Answer the follow questions with m = 6 bits and the window size is 63. We assume each event is independent. a. The send machine is in the ready state with S f = 10 and S n = 15. What is the sequence number of the next packet to send? b. The send machine is in the ready state with S f = 10 and S n = 15. A time-out occurs. How many packets are to be resent? What are their sequence numbers? c. The send machine is in the ready state with S f = 10 and S n = 15. An ACK with ackno = 13 arrives. What are the next values of S f and S n?

4 Problem #7. Assume we need to design a Selective-Repeat slid-window protocol for a network in which the bandwidth is 1 Gbps and the average distance between the sender and receiver is 5,000 km. Assume the average packet size is 50,000 bits and the propagation speed in the media is m. a. Find the maximum size of the send and receive windows. b. Find the number of bits in the sequence number field (m). c. Find an appropriate time-out value for the timer.

5 Problem #8. An HTTP client opens a TCP connection us an initial sequence number (ISN) of 14,534 and the ephemeral port number of 59,100. The server opens the connection with an ISN of 21,732. Show the three TCP segments dur the connection establishment if the client defines the rwnd of 4000 and the server defines the rwnd of Ignore the calculation of the checksum field.

6 Problem #9. In TCP, assume a client has 100 bytes to send. The client creates 10 bytes at a time in each 10 ms and delivers them to the transport layer. The server acknowledges a segment when there is a previous segment that has not been acknowledged (every other segment) or if a timer times out at 60ms. The round-trip time is 20ms, but the sender timer is set to 100ms. a. Show the time line for the segments and the bytes each segment carries if the implementation uses Nagle s algorithm with maximum segment size (MSS) of 30 bytes. b. Does any segment carry the maximum segment size?

7 Problem #10. If originally RTT S = 14 ms and α is set to 0.2, calculate the new RTT S after the follow events (times are relative to Event 1): - Event 1: 00 ms Segment 1 was sent. - Event 2: 06 ms Segment 2 was sent. - Event 3: 16 ms Segment 1 was timed-out and resent. - Event 4: 21 ms Segment 1 was acknowledged. - Event 5: 23 ms Segment 2 was acknowledged.

8 Wireshark Note: Provide Wireshark screenshots for all the problems. Problem #11. Run wireshark and set the display filter to only show traffic between client (your system) and the course page. Then open the monet.skku.ac.kr -> courses -> details -> syllabus. After this stop the capture in wireshark and show the comparison between TCP data segments and total TCP packets between client and server us IOgraph Problem #12. Run wireshark and set the display filter to only show traffic between client (your system) and the course page. Then open the monet.skku.ac.kr -> courses -> details -> syllabus. After this stop the capture in wireshark and show the comparison between the total TCP Seq messages, TCP Ack messages and TCP non-zero ACK message us IOgrpah. Also write that what you analyze from this graph