[試題] 100下 周承復 計算機網路 期中考
課程名稱︰計算機網路
課程性質︰必修
課程教師︰周承復
開課學院：電資學院
開課系所︰資工系
考試日期（年月日）︰2012/4/18
考試時限（分鐘）：180 min
是否需發放獎勵金：是
（如未明確表示，則不予發放）
試題 :
Computer Network Midterm 2012
Question 1: "Quickies"
(a)(5%) What are two fundamental advantages of peer-to-peer(P2P) systems over
client-server systems?
(b)(5%) Optimistic unchoking in BitTorrent allows a peer to download the
entire file without uploading anything. Ture or false? Explain.
(c)(5%) What is one similarity and one difference between connection manage-
ment in HTTP/1.0 and FTP?
(d)(5%) What protocol is being used between your browser and a mail sever such
as Hotmail or Gmail?
(e)(10%) NTU Computer and Information Networking Center hires you as the p2p
expert to reduce its rising bandwidth costs due the rising use of BitTorrent.
How would you address their problem.
(f)(10%) List four factors that contribute to the end-to-end delay in a packet-
switched network. Which of these are constant and which of these depend on the
load in the network?
(g)(10%) Suppose you would like to urgently deliver 40 terabytes data from
Boston to Los Angeles. You have available a 100Mbps dedicated link for data
transfer. Would you prefer to transmit the data via this link or instead use
Fedex overnight delivery? Explain.
Question 2: "DNS"
(a)(5%) If we know a host name(tw.yahoo.com), how could we figure out its IP
address?
(b)(5%) How could we figure out the mail server(including host name) in our
CSIE dept.?
(c)(5%) How could we find out the name server in our CSIE dept.?
Question 3: "Web"
Consider an http client that wants to retrieve a WWW document at a given URL.
The IP address of the http server is initially unknown. The WWW object at the
URL has one embedded GIF image that resides at the same server as the original
object.
a.(10%) What transport and application layer protocols besides http are needed
in this scenario?
b.(10%) Suppose that the time needed to contact and receive a reply from any
server(for any protocol) is RTT, and the time to trandmit the WWW object and
GIF image is T. How much time(in RTT and T) is needed from when the user first
enters the URL until the complete document is displayed? Assume that non-
persistent http is used. Consider the delays of all protocols in your answer,
not just those of http.
Question 4: "TCP"
(10%) Suppose a web server has 600 ongoing TCP connections. How many server-
side sockets are used? How many server-side port numbers are used? Briefly
(two sentences at most each) explain your answer.
Question 5: "delay"
(10%) Consider two packet switches directly connected by a link of 5000 km,
propagation speed 2.5*10^8 m/s, and transmission rate 1 Mbps. How long does it
take to move a packet of length 1000 bytes from one packet switch to the other
packet switch? Generally, how long does it take to move a packet of length L
over a link of distance d, propagation speed s, and transmission rate R bps?
Question 6: "Delivery"
(10%) Suppose that data is being output at a sensor at 1 sample per second. It
is important for the receiver to have the most recent value of the sensor's
reading, rather than all values(for example, it is better for the receiver to
get a current value, rather than an outdated value). Would you use TCP or UDP
to send this sensor data? Why?
Question 7: "Socket Programming"
(a)(5%) What is socket and what is it used to?
(b)(5%) Which functions will be executed before creating the connection-
oriented welcoming socket, which the server uses to perform an accept()?
(c)(5%) From above, once the accept() is done, does the server use the
welcoming socket to communicate back to the client? Explain your answer.
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