课程名称︰计算机网路 课程性质︰必修 课程教师︰周承复 开课学院：电资学院 开课系所︰资工系 考试日期（年月日）︰2012/4/18 考试时限（分钟）：180 min 是否需发放奖励金：是 （如未明确表示，则不予发放） 试题 : 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. --

※ 发信站: 批踢踢实业坊(ptt.cc) ◆ From: 140.112.30.138 ※ 编辑: fei6409 来自: 140.112.30.138 (04/18 16:22)