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課程內容：計算機網路
課程性質：系必修
課程教師：周承復
開課學院：電資
開課系所：資工
考試日期(年月日)：2011.4.20
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 :
1.
(a)(5%)
Give an example of a stateless application layer protocol.
(b)(10%)
Supposw a web server has 800 ongoing TCP connections. How many
serveer-side sockets are used? How many server-side port numbers
are used?
Briefly(two sentences at most each) explain your answer.
(c)(10%)
Give two examples of application layer protocols and their port
numbers
(d)(10%)
How doew the transport layer manage to perform application
multiplexing and de-mutiplexing?
(e)(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?
(f)(10%)
Please explain what DHT(Distributed Hash Table) is, and how it works.
In addition, how we can improve the performance of searching in DHT
from 0(N) to 0(log N), where N is the total number of peers in DHT
systems.
(g)(10%)
Please explain the mechanisms "tit-for-tat" and "optimistically
unchoke" in BitTorrent.
2.(15%)
Consider sending a large file of F bits from host A to host B. A and B are
connected by path of L links, and the links are uncongested(that is ,no
queuing delays). Host A cuts the file into segments of S bits each(we assume
here that F is a mulltiple of S) and adds h bits of header to each segments,
forming packets of S+h bits. Each link 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. Neglect propagation delay.
3.(20%)
Question：A reliavle data transfer protocol
Considera sender and receiver that are connected by a sender-to-receiver
channel that can corrupt and lose packets. The receiver-to-sender channel is
perfect(i.e., it will nnot lose or corrupt packets). The delay on each channel
is known to always be less than some maximum value, d. Neither channel will
reorder packets. [Note：re-read the channel properties just descrived and make
sure you understand them!] You are to design a reliable data transfer protocol
for this scenario using only those mechanisms(among the four listed above)
that are absolutely required. That is, if you use a mechanism that is not
required, your answer will not given full creditt, even if the protocol works.
Your protocol should be as simple as possible but have the functionality to
reliably deliver data under the stated assumptions. Your solution need not be
efficient； it must work correctly.
4.
(a)(5%)
According to "The Design Philosophy of the DARPA Internet Protocols"
Which technique for multiplexing ded DARPA choose (circuit-switching
of packet-switching of others)? Why?
(b)(5%)
There are some goals with priority for the internet architecture in
hte paper. If we want to apply the goals to the interner today, should
we change the priorty of those goals?
Explain wht or why not.
5.(10%)
Just choose one to answer
(1)According to the papaers about cloud computing you have read, please list
two disadvantage to be improved of cloud computing. Also give your reason
briefly.
(2)What is Iaas, SaaS, PaaS
6.(5%)
Suppose k packets arrive simultaneously to a link at which no packets are
currently being transmitted or queued. Each packet is of length S and the link
has transmission rate T.
What is the average queuing delay for the k packets?
7.(5%)
Suppose within your Web browser you click on a link to obtain a Web page. The
IP address for the associated URL is not cached in your local host, so a DNS
lookup is necessarry to obtain the IP address. Suppose that k DNS servers are
visited before your host receives the IP address from DNS; the successive
visits incur an Round-Trip Time of T1, T2, ...., Tk.
Further suppose that the Web page associated with the link contains three
objects, consisting oof one HTML text objevt and two small images on the same
server. Let T0 denote the Round-Trip Time between the local host and the
server containing the objects. Assuming zero transmission tme of the objects.
Also assuming the connection is non-persistent and non-parallel. How much time
elapses from when the client clicks on the link until the client receives all
the objects?
--
解方塊不需要思考 但是思考會讓解方塊更有意義
by aegius1r
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