Preview Test: HW3. Test Information Description Due:Nov. 3

Transcription

1 Preview Test: HW3 Test Information Description Due:Nov. 3 Instructions Multiple Attempts Not allowed. This test can only be taken once. Force Completion This test can be saved and resumed later. Question Completion Status: Save and Submit QUESTION 1 UDP and TCP use 1s complement for their checksums. Suppose you have the following three 8- bit bytes: , , What is the 1s complement of the sum of these 8- bit bytes? QUESTION 2 Suppose Host A sends one segment with sequence number 38 and 4 bytes of data over a TCP connection to Host B. In this same segment the acknowledgment number is necessarily 42. QUESTION 3 In TCP, the acknowledgement number that a host puts in a segment is the sequence number of the next byte the host is expecting from the sender. QUESTION 4 The size of the TCP rwnd never changes throughout the duration of the connection. QUESTION 5 The TCP segment has a field in its header for rwnd.

2 QUESTION 6 Suppose Host A sends two TCP segments back to back to Host B over a TCP connection. The first segment has sequence number 90; the second has sequence number 110. a. How much data is in the first segment? b. Suppose that the first segment is lost but the second segment arrives at B. In the acknowledgment that Host B sends to Host A, what will be the acknowledgment number? Write your answer with the above order. QUESTION 7 Pipelining requires which of the following transmitting many packets before receiving acknowledgements unique sequence numbers for each in-transit packet sender-side buffering of unacknowledged packets all of the above QUESTION 8 UDP has which of the following characteristics: three-way hand shake for connection establishment regulated send rate connection state at the server none of the above QUESTION 9 Given GBN protocol scenario in below diagram, describe what would happen for each of the numbered time ((10 through (5)) instants. Assume the sender s window size may hold 5 packets

3 10 points QUESTION 10 Given Selective-Repeat protocol scenario in below diagram, describe what would happen at each numbered ((1) through (6))time instants. Also, describe the contents of sender and receiver s windows at each of these time instants. When you describe the contents of the sender window s contents, identify the packets which are acknowledged. When you describe the contents of the receiver window s contents, identify the packets which are buffered but can t be delivered to the application. Assume the sender s and receiver s windows may hold 6 packets each.

4 QUESTION 11 The MSS is the maximum size of a TCP segment including headers. 12 points QUESTION 12 Suppose Host A is sending Host B a large file over a TCP connection. The number of unacknowledged bytes that A sends cannot exceed the size of the receive buffer. QUESTION 13 Over a TCP connection, suppose host A sends two segments to host B, host B sends an acknowledgement for each segment, the first acknowledgement is lost, but the second acknowledgement arrives before the timer for the first segment expires. Host A will retransmit the first segment Host A will retransmit the second segment

5 Host A will retransmit neither segments Host A will retransmit both segments QUESTION 14 Describe about threeway handshaking QUESTION 15 When a UDP segment arrives to a host, in order to direct the segment to the appropriate socket, the OS uses the source port number the destination port number the source IP address all of the above QUESTION 16 Consider the following diagram for connection oriented demultiplexing process. Fill out 4 numbered fields ((1) through (4)) with proper port numbers. QUESTION 17 TCP applies fast retransmit to a segment when 8 points the segment's timer expires when it receives three ACKs for an earlier segment

6 it estimates unusually large RTTs none of the above