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
Trang 17Chỗ này hiểu là fragment 2 bắt đầu ởbyte thứ 376, xong tính offset=376/8=47
Trang 245 BC nhé
Trang 50Hình ko phân bi ệ t dc TCP1 vs TCP2,
Trang 56- 2 ch ỗ này ngag nhau mk v ẽ h ơ i l ệ ch :))
Trang 74Communication Networks (2 Edition) Chapter 6 Solutions
10 A channel using random access protocols has three stations on a bus with end-to-end propagation delay τ
Station A is located at one end of the bus, and stations B and C are together located at the other end of the bus
Frames arrive at the three stations and are ready to be transmitted at stations A, B, and C at the respective times tA =
0, tB = τ/2, and tC = 3τ/2 Frames require transmission times of 4τ In appropriate figures, with time as the horizontal
axis, show the transmission activity of each of the three stations for
Frame arrival times:
No ACK; C times out, reschedules
collision
collision
No ACK; B times out, reschedules
Station C senses channel busy and backs off
Trang 75Communication Networks (2 Edition) Chapter 6 Solutions
B detects collision, aborts
A detects collision, aborts
11 Estimate the maximum throughput of the CDPD system assuming packets are 1096 bytes in length
Hint: What is a for this system?
Solution:
During the contention interval, it takes two microblock delays (2tµblock) for a station to know if it has
captured the reverse channel Divide the time into minislots of 2tµblock
As in the CSMA-CD system, the maximum probability of successful transmission is
e
Psuccessmax = 1, and
P J E
success
=
= max1 ]
The maximum throughput occurs when the channel time is spent in packet transmission followed by a
contention period After the packet transmission E[X], each station spends one tµblock to determine if
the channel is idle or busy
The maximum throughput is given by
a e t
e t
X E
X E
ublock ublock 1 ( 2 1 )
1 )
2 ( ]
[
] [
]
[X E
bits
tublock 3 1
200 , 19
=
Assume the packet is already in HDLC format
bits bytes 8768
Trang 893 (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.
B2
B3 B1
a) (5pts) Suppose host J sends a frame to host C List the hosts that receive the frame.
Trang 90a) Assume no fast retransmission or fast recovery Draw the time diagram showingeach segment and acknowledgement until the entire file is transferred Indicate on thediagram all changes in the cwnd and ssthresh How long does it take to transfer thefile?
b) Answer part (a) assuming TCP Reno, i.e., the TCP version that implements bothfast retransmission and fast recovery
c) Answer part (b) assuming that only the 6th segment is dropped
acknowledg-• 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 firstsegment is sent until the acknowledgement of the last segment is received
7Câu 2 đề này nó l ấ y ở đ ây!!
Trang 91cwnd=3
X
Transfer Time=10*d (b)
cwnd=3
X
Transfer Time=10*d (c) TIMEOUT
Notes: People lost the most number of points on this problem People indicated on theirtiming diagrams that segments 5,6 and 7 are resent; I automatically deducted 2.5 pts forthe first subproblem, and 2 pts for the second subproblem if you did this You shouldknow 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 readthe lecture notes about the ACKing conventions; I explicitly posted on moodle that youshould review those conventions before doing this problem Also, note that when youinflate your window in b), the sender has the ability to send out one additional segment,namely, 8 I included an additional subproblem c) if you would like more practice onthis type of problem
8