[試題] 102上 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：資訊工程系
開課系所︰電機資訊學院
考試日期（年月日）︰2013年11月7日
考試時限（分鐘）：180
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 2013
Question 1:"Quickies"
(40%)Answer each of the following questions briefly, i.e. in at most a few
sentences.
a) (10%)What does it mean for HTTP1.1 to be "persistent"? What is the value of
HTTP1.1 being persistent, as opposed to being non-persistent, as in HTTP1.0?
b) (10%)What is the difference between a recursive query and an iterated query
in the DNS?
c) (10%)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. What transport and application layer protocol besides http are needed in
this scenario?
b. Suppose that the time needed to contact and receive a reply from any
server(for any protocol) is RTT, and the time to transmit 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 2:"DHT"
(35%)Distributed Hash Table(DHT)
(a)(5%)What are two fundamental advantages of peer-to-peer(P2P) systems over
client-server systems?
(b)(20%)Consider a circular Distributed Hash Table(DHT) with node identifiers
in the range[0:15]. Suppose there are seven peers with identifiers
1,2,4,6,8,11 and 13.
(i) Suppose that the following(key,value) pairs should be stored in the DHT:
(2,1),(6,4),(7,15)and(15,4). Which peers will store which (key,value)
pairs? Fill in the table below.
(key,value) Identifier of the responsible peer
( 2, 1)
( 6, 4)
( 7,15)
(15, 4)
(ii)Suppose that peer 4 learns that peer 6 has left the DHT. How does peer 4
updates its successor state information? Which peer is now its first
successor? Its second successor?
(c)(10%)Explain how DHT improves search performance from O(n) to O(log n),
where n is the total number hosts in DHT method.
Question 3:"DNS"
(10%)For a new startup company "Network Utopia" and we would like to register
name networkuptopia.com at DNS registrar. Suppose that this new startup
company domain is "networkutopia.com", the dns server is "dns1.networkutopia.
com", and its IP address is "212.212.212.1", the registrar needs to insert what
DNS comments are in com TLD server.
Question 4:"Transmission Delay"
(20%)Consider sending a large file of F bits from Host A to Host B. As shown in
the following diagram, there are four links and three switches between A and B,
and the links are uncongested(that is, no queuing delays). Host A segments the
file into segments of S bits each and adds 90 bits of header to each segment
forming packets of L = 90 + S bits. Each links has a transmission rate of R bps
. Find the value of S that minimizes the delay of moving the file from Host A
to Host B. Disregard propagation delay.
Question 5:"Homework"
(15%)Suppose 100 users share a single link, and packet-switching is used.
At any given time, the probability if a user is transmitting is p. Find the
probability that exactly n users is transmitting simultaneously.
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◆ From: 140.112.16.140
※ 編輯: danielu0601 來自: 140.112.16.140 (11/07 11:20)
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