Tổng hợp đề thi Mạng máy tính ET4230 Đại học Bách khoa Hà Nội (có đáp án, lời giải chi tiết)

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Ngày đăng: 15/03/2020, 16:36

Tổng hợp đề thi mạng máy tính (Đại học Bách khoa Hà Nội). Tài liệu tổng hợp đề thi các kì môn Mạng máy tính (ET4230), viện Điện tử Viễn thông, Đại học Bách khoa Hà Nội, có lời giải và đáp án chi tiết Bản gốc câu đeiii! (15 pts) Learning bridges Consider the extended LAN shown below Assume all bridges were just turned on and no frames have been sent Three frames are subsequently sent in the order described below A B B2 C D B1 E F B3 G H J a) (5pts) Suppose host J sends a frame to host C List the hosts that receive the frame A, B, C, D, E, F, G, and H b) (5pts) Afterwards, host E sends a frame to J What hosts receive that frame? F, H, and J c) (5pts) Finally, host D sends a frame to E Which hosts receive this frame? A and E Câu đề lấy đây!! TCP/Congestion Control Host A sends a file consisting of MSS-sized segments to a host B using TCP Assume that the 4th segment in the transmission is lost Assume the retransmission timeout is T, the one-way latency is d, and that T > 4*d Ignore the transmission time of the segments and of the acknowledgements Also, assume the TCP three-way handshake has completed, but no data has been transmitted a) Assume no fast retransmission or fast recovery Draw the time diagram showing each segment and acknowledgement until the entire file is transferred Indicate on the diagram all changes in the cwnd and ssthresh How long does it take to transfer the file? b) Answer part (a) assuming TCP Reno, i.e., the TCP version that implements both fast retransmission and fast recovery c) Answer part (b) assuming that only the 6th segment is dropped Notes • For Fast Recovery, assume that each duplicate acknowledgment increases cwnd by • For Fast Recovery, assume that, upon receiving a non-duplicate acknowledgment, cwnd drops back to ssthresh • If the value of cwnd is fractional, you should round it to the closest larger integer • The transfer time is the time interval measure at source A from the time the first segment is sent until the acknowledgement of the last segment is received Answer cwnd=1 A cwnd=2 B cwnd=1 A B cwnd=2 2,3 4,5,6,7 X 5,6,6 cwnd=6 4,8 8,9 cwnd=2 cwnd=2 cwnd=3 3,4 4,4,4 cwnd=5, ssthresh=2 8,9 2,3 X4,5,6,7 4,4,4 B cwnd=4 X4,5,6,7 cwnd=1, ssthresh=2 cwnd=2 3,4 cwnd=4 TIMEOUT A 2,3 3,4 cwnd=4 cwnd=1 10 cwnd=3 6,6 cwnd=6, ssthresh=3 cwnd=3 10 9,10 Transfer Time=8*d + T (a) Transfer Time=10*d (b) Transfer Time=10*d (c) Notes: People lost the most number of points on this problem People indicated on their timing diagrams that segments 5,6 and are resent; I automatically deducted 2.5 pts for the first subproblem, and pts for the second subproblem if you did this You should know by now (after doing the project and seeing this material in lecture/discussion) that the receiver has a buffer to place out of order segments Also, people forgot to read the lecture notes about the ACKing conventions; I explicitly posted on moodle that you should review those conventions before doing this problem Also, note that when you inflate your window in b), the sender has the ability to send out one additional segment, namely, I included an additional subproblem c) if you would like more practice on this type of problem ... Chỗ hiểu fragment bắt đầu byte thứ 376, xong tính offset=376/8=47 ko phải bắt đầu byte thứ 47, mk ghi nhầm chỗ Phải chia offset tính theo "8-byte chunk" Fragment cx tương tự nhé! D
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