quiz 2.txt

这是 ssd8 exam1 的选择题 比较全 感兴趣的 朋友 可以 参考一下

	Correct answer is 	(c)

	Your score on this question is: 	0.00

	Feedback: 	
   See section 1.2.6 of the course notes. 	

	3. 	
	The point-to-point (PPP) protocol

   1. can only be used in analog dial-up connections
   2. is a data-link protocol
   3. can only be used to carry IP over serial lines

	

	(a) II and III only
(b) II only
(c) III only
(d) I and II only

	Correct answer is 	(b)

	Your score on this question is: 	10.00

	Feedback: 	
   See section 1.2.5 of the course notes. 	

	4. 	
	After the phone company installs a T1 trunk to an office building, which of the following can it provide to the tenants of the building? Recall that a T1 trunk has a capacity of 1.544 Mbps, and that a voice channel requires an isolated 3 KHz channel.

   1. 20 new telephone lines and a 200 Kbps digital data channel
   2. A single 1.1 Mbps data channel
   3. 25 new telephone lines

	

	(a) I, II, and III
(b) I and II only
(c) II only
(d) none

	Correct answer is 	(b)

	Your score on this question is: 	10.00

	Feedback: 	
   See section 1.2.1 of the course notes. 	

	5. 	
	The maximum binary data throughput of a cable that cleanly transmits a range of frequencies up to 100 MHz is 	

	(a) within 80 and 120 megabits per second
(b) exactly 200 megabytes per second
(c) exactly 200 megabits per second
(d) currently 56 Kbps but more as modem technology improves

	Correct answer is 	(c)

	Your score on this question is: 	10.00

	Feedback: 	
   See section 1.2.1 of the course notes. 	

	6. 	
	A fiber optic is found to be able to deliver light cleanly in a frequency range 25,000 GHz wide. This fiber can be used to create the following type of channel between two routers

   1. a single 50 terabits per second (Tbps = 1,000 Gbps) data channel
   2. 5 2-Gbps data channels
   3. one video channel but no data channels, because data cannot be encoded in light beams

	

	(a) III only
(b) I and II only
(c) II only
(d) I only

	Correct answer is 	(c)

	Your score on this question is: 	0.00

	Feedback: 	
   See section 1.2.1 of the course notes.
   (b) The electronics that interface to the fiber cannot process more than a few GHz of bandwidth in a single channel. 	

	7. 	
	A specific CSMA-CD network such as 10-BASET "Ethernet" 	

	(a) works best for an even number of nodes
(b) can connect very distant nodes
(c) has higher cost per node as nodes are added
(d) suffers performance degradation as nodes are added

	Correct answer is 	(d)

	Your score on this question is: 	10.00

	Feedback: 	
   See section 1.2.4 of the course notes. 	

	8. 	
	A sender's data link layer uses "bit stuffing" to 	

	(a) mark the start and the end of a frame
(b) pad the data so that it has an even length for parity calculations
(c) force the receiver to enlarge its flow control window
(d) avoid confusing data bits with control bits

	Correct answer is 	(d)

	Your score on this question is: 	10.00

	Feedback: 	
   See section 1.2.2 of the course notes. 	

	9. 	
	What is the type of an "8+1" parity code that outputs 100101011? 	

	(a) Odd Parity
(b) Even Parity
(c) Null Parity
(d) Cannot tell since we do not know which bit is the parity bit

	Correct answer is 	(a)

	Your score on this question is: 	10.00

	Feedback: 	
   See section 1.2.2 of the course notes. 	

	10. 	
	A cable is rated at 19200 baud. A 19200 baud cable is guaranteed to transmit a signal successfully that has the potential to change 19200 times per second. The maximum throughput of this cable, assuming a sensible encoding, 	

	(a) is between 19200 and 38400 bits per second, depending on the bit pattern of the transmitted data
(b) is less than 19200 bits per second
(c) can be any number greater than or equal to 19200 bits per second, depending on the way the data is encoded into signal voltages
(d) is exactly 19200 bits per second

	Correct answer is 	(c)

	Your score on this question is: 	10.00
 1. 
 A university has 20 computers in a laboratory that is currently served by several small 10 Base-T "Ethernet" hubs that are directly connected to each other. The network performance has been found to be lacking, and an upgrade is planned. The computers are identical and place a comparable load on the network that is relatively constant and modest for each computer (in the order of 500 Kbps). What would you suggest for the upgrade?  
 

  (a) A new bank of dial-up modems
 (b) Replace the hubs with 100 Base-T hubs
 (c) Replace the hubs with 10 Base-T switches
 (d) A small 10 Base-T switch to connect the existing hubs  

 Correct answer is  (d)  

 Your score on this question is: 10.00  

 Feedback: 
   See section 1.2.4 of the course notes.  
 

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 2. 
 Which of the following are responsibilities of the data link layer? 
Noticing transmission errors 
Regulating transmission speed when a receiver is overwhelmed 
Regulating transmission speed when any of several IP routers in a network path are overwhelmed 
 
 

  (a) I and II only
 (b) I only
 (c) II and III only
 (d) I, II, and III  

 Correct answer is  (a)  

 Your score on this question is: 0.00  

 Feedback: 
   See section 1.2.2 of the course notes.
   (d) The data link layer only deals with one link, not with routers.  
 

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 3. 
 What is the type of an "8+1" parity code that outputs 100101011?  
 

  (a) Cannot tell since we do not know which bit is the parity bit
 (b) Even Parity
 (c) Null Parity
 (d) Odd Parity  

 Correct answer is  (d)  

 Your score on this question is: 0.00  

 Feedback: 
   See section 1.2.2 of the course notes.  
 

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 4. 
 A packet-switched network uses switches that schedule packets using a first-in-first-out (FIFO) discipline. Several people want to carry out a conference over this network. The conference is carried out via typed text for the most part, but, occasionally, one of the parties has to send a large video. This happens very rarely. Which of the following switching approaches is most suitable for this application?  
 

  (a) Circuit-switched
 (b) Space-switched
 (c) Message-switched
 (d) Packet-switched  

 Correct answer is  (d)  

 Your score on this question is: 0.00  

 Feedback: 
   See section 1.2.3 of the course notes.
   (a) A circuit allocates a specific bandwidth to the conference. If this is high enough for the video, bandwidth will be mostly wasted; if this is low enough for efficiency, the video will take a very long time.  
 

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 5. 
 A cable is rated at 19200 baud. A 19200 baud cable is guaranteed to transmit a signal successfully that has the potential to change 19200 times per second. The maximum throughput of this cable, assuming a sensible encoding,  
 

  (a) can be any number greater than or equal to 19200 bits per second, depending on the way the data is encoded into signal voltages
 (b) is between 19200 and 38400 bits per second, depending on the bit pattern of the transmitted data
 (c) is less than 19200 bits per second
 (d) is exactly 19200 bits per second  

 Correct answer is  (a)  

 Your score on this question is: 0.00  

 Feedback: 
   See section 1.2.1 of the course notes.  
 

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 6. 
 Collision Detection improves the throughput of multiple access networks because 
it can shorten the length of garbled frames 
it can decrease the number of garbled frames 
it delays by a random amount of time when a collision is detected 
 
 

  (a) II and III only
 (b) I, II, and III
 (c) I and II only
 (d) I only  

 Correct answer is  (c)  

 Your score on this question is: 0.00  

 Feedback: 
   See section 1.2.4 of the course notes.
   (b) Choice III is true regardless of whether or not collision detection is used.  
 

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 7. 
 In the year 2000, telephone and cable television companies are competing for the home Internet market. A typical offering of ADSL by the telephone companies is for a 1.5 Mbps link into the home, while a common offering by the cable television companies is for a shared 27 Mbps link into the home. The cost is usually comparable for these two options. Suppose you want to display the images at home that are constantly sent over the Internet by a security camera elsewhere. The camera has a relatively low refresh rate and the transmission will approximately require a constant 300 Kbps. Of course, you will also want to use your computer to surf the Internet. Which of the following would be valid arguments to get a cable modem instead of ADSL? 
The cable modem always has better bandwidth and latency than ADSL. 
The cable TV company has more experience transmitting analog video. 
The camera is connected to the Internet via the same cable TV company 
 
 

  (a) I only
 (b) I, II, and III
 (c) I and III only
 (d) III only  

 Correct answer is  (d)  

 Your score on this question is: 0.00  

 Feedback: 
   See section 1.2.5 of the course notes.  
 

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 8. 
 A parity code is a(n)  
 

  (a) duplex transmission technique
 (b) error-detecting code
 (c) error-correcting code
 (d) fair resource allocation scheme  

 Correct answer is  (b)  

 Your score on this question is: 10.00  

 Feedback: 
   See section 1.2.2 of the course notes.  
 

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 9. 
 The point-to-point (PPP) protocol 
can only be used in analog dial-up connections 
is a data-link protocol 
can only be used to carry IP over serial lines 
 
 

  (a) II only
 (b) I and II only
 (c) III only
 (d) II and III only  

 Correct answer is  (a)  

 Your score on this question is: 0.00  

 Feedback: 
   See section 1.2.5 of the course notes.  
 

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 10. 
 Which of the following statements most closely agrees with your position regarding the reliability of the service provided by the data link layer?  
 

  (a) The data link layer need not be concerned with reliability because the physical layer is perfectly reliable.
 (b) The data link layer must provide connection-oriented service because it must retransmit lost data and eliminate duplicate data.
 (c) The data link layer need not retransmit data, but must acknowledge received data because it must detect lost data.
 (d) The data link layer's concern with reliability is an optimization, not a requirement.  

 Correct answer is  (d)  

 Your score on this question is: 0.00  

 Feedback: 
   See section 1.2.2 of the course notes.  


 7. 
 A university has 20 computers in a laboratory that is currently served by several small 10 Base-T "Ethernet" hubs. The network performance has been found to be lacking, and an upgrade is planned. The computers usually have modest network needs (in the order of 500 Kbps), but one or two are occasionally used to receive high-quality remote video streams that require in the order of 10 Mbps. No more than two computers are used for this purpose at any given time, but any two may be used for this application. What would you suggest for the upgrade?  
 

  (a) Replace the hubs with 10 Base-T switches
 (b) A 10 Base-T bridge to connect several existing hubs
 (c) A new bank of dial-up modems
 (d) Replace the hubs with 100 Base-T hubs  

 Correct answer is  (d)  

 Your score on this question is: 0.00  

 Feedback: 
   See section 1.2.4 of the course notes.
   (b) This will not provide enough bandwidth for the video application to any computer.