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

1. 	
	In contrast to message switching, packet switching

   1. needs to find a "copper" path to the receiver before transmitting any data
   2. offers a better upper bound on transmission delay
   3. suffers from greater overhead at the endpoints

	

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

	Correct answer is 	(d)

	Your score on this question is: 	10.00

	Feedback: 	
   See section 1.2.3 of the course notes. 	

	2. 	
	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) III only
(c) II only
(d) I and II only

	Correct answer is 	(c)

	Your score on this question is: 	10.00

	Feedback: 	
   See section 1.2.5 of the course notes. 	

	3. 	
	When the data link layer applies "framing" to the data to be transmitted, it 	

	(a) enhances it with extra data that permits the receiver to synchronize with the sender
(b) adds the protocol headers from higher layers to the data before it transmits it
(c) cuts out the headers from higher layer protocols before transmission
(d) inserts flags to draw attention to high-priority data within a transmission

	Correct answer is 	(a)

	Your score on this question is: 	0.00

	Feedback: 	
   See section 1.2.2 of the course notes. 	

	4. 	
	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) Odd Parity
(c) Even Parity
(d) Null Parity

	Correct answer is 	(b)

	Your score on this question is: 	10.00

	Feedback: 	
   See section 1.2.2 of the course notes. 	

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

	Correct answer is 	(b)

	Your score on this question is: 	10.00

	Feedback: 	
   See section 1.2.1 of the course notes. 	

	6. 	
	In a broadcast-based network, longer propagation delays 	

	(a) significantly decrease the benefit of sensing the carrier before transmitting
(b) make it all the more critical to sense the carrier before transmitting
(c) do not affect the cost-benefit trade-off of carrier sensing
(d) destroy the carrier, making it impossible to sense it before transmitting

	Correct answer is 	(a)

	Your score on this question is: 	10.00

	Feedback: 	
   See section 1.2.6 of the course notes. 	

	7. 	
	The maximum binary data throughput of a cable that cleanly transmits a range of frequencies up to 100 MHz is 	

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

	Correct answer is 	(d)

	Your score on this question is: 	10.00

	Feedback: 	
   See section 1.2.1 of the course notes. 	

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

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

	Correct answer is 	(b)

	Your score on this question is: 	10.00

	Feedback: 	
   See section 1.2.2 of the course notes. 	

	9. 	
	Why do not all network switches use crossbars in their switching fabric?

   1. For a given number of ports, crossbars are more expensive.
   2. Crossbars are more likely to block connections unnecessarily between ports that are idle.
   3. Crossbar designs are too simple.

	

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

	Correct answer is 	(b)

	Your score on this question is: 	0.00

	Feedback: 	
   See section 1.2.3 of the course notes. 	

	10. 	
	A parity code is a(n) 	

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

	Correct answer is 	(d)

	Your score on this question is: 	10.00

1. 	
	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) Null Parity
(c) Odd Parity
(d) Even Parity

	Correct answer is 	(c)

	Your score on this question is: 	10.00

	Feedback: 	
   See section 1.2.2 of the course notes. 	

	2. 	
	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) I and II only
(b) II only
(c) II and III only
(d) III only

	Correct answer is 	(b)

	Your score on this question is: 	10.00

	Feedback: 	
   See section 1.2.5 of the course notes. 	

	3. 	
	Which of the following are responsibilities of the data link layer?

   1. Noticing transmission errors
   2. Regulating transmission speed when a receiver is overwhelmed
   3. Regulating transmission speed when any of several IP routers in a network path are overwhelmed

	

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

	Correct answer is 	(b)

	Your score on this question is: 	10.00

	Feedback: 	
   See section 1.2.2 of the course notes. 	

	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) Message-switched
(b) Space-switched
(c) Circuit-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.
   (c) 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. 	

	5. 	
	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) II only
(b) I and II only
(c) I only
(d) III only

	Correct answer is 	(a)

	Your score on this question is: 	10.00

	Feedback: 	
   See section 1.2.1 of the course notes. 	

	6. 	
	Radio stations are able to share the AM (Amplitude Modulation) spectrum by using _____ multiplexing 	

	(a) time-division
(b) wavelength-division
(c) phase shift
(d) frequency-division

	Correct answer is 	(d)

	Your score on this question is: 	10.00

	Feedback: 	
   See section 1.2.1 of the course notes. 	

	7. 	
	Why do not all network switches use crossbars in their switching fabric?

   1. For a given number of ports, crossbars are more expensive.
   2. Crossbars are more likely to block connections unnecessarily between ports that are idle.
   3. Crossbar designs are too simple.

	

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

	Correct answer is 	(b)

	Your score on this question is: 	10.00

	Feedback: 	
   See section 1.2.3 of the course notes. 	

	8. 	
	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's concern with reliability is an optimization, not a requirement.
(b) The data link layer need not retransmit data, but must acknowledge received data because it must detect lost data.
(c) The data link layer need not be concerned with reliability because the physical layer is perfectly reliable.
(d) The data link layer must provide connection-oriented service because it must retransmit lost data and eliminate duplicate data.

	Correct answer is 	(a)

	Your score on this question is: 	10.00

	Feedback: 	
   See section 1.2.2 of the course notes. 	

	9. 	
	In contrast with wireless communication, "wired" communication

   1. does not suffer from attenuation and interference
   2. can use any frequencies without a license
   3. always has more throughput

	

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

	Correct answer is 	(a)

	Your score on this question is: 	10.00

	Feedback: 	
   See section 1.2.1 of the course notes. 	

	10. 	
	In contrast to message switching, packet switching

   1. needs to find a "copper" path to the receiver before transmitting any data
   2. offers a better upper bound on transmission delay
   3. suffers from greater overhead at the endpoints

	

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

	Correct answer is 	(d)

	Your score on this question is: 	10.00

1. 	
	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 need not retransmit data, but must acknowledge received data because it must detect lost data.
(c) The data link layer must provide connection-oriented service because it must retransmit lost data and eliminate duplicate 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: 	10.00

	Feedback: 	
   See section 1.2.2 of the course notes. 	

	2. 	
	If you have seen any mobile telephone antennas, you will have noticed that they have groups of radiating elements facing different directions. Most antennas we know are arranged in a triangle, so that each group spans a 120-degree arc of the horizon, but we have also seen squares in which each group spans a 90-degree arc instead. There is one such arrangement for each cell of a mobile phone system. This sort of base station is unsightly and expensive. A cell could instead use a single omnidirectional antenna that would be simple and inconspicuous. Why do you think the more complicated designs are used? 	

	(a) To decrease frequency reuse without the need for time-division multiplexing
(b) To decrease the number of times a call must be handed off from one base station to another.
(c) To increase frequency reuse without having to build more antenna towers
(d) To allow the use of switches based on space-division multiplexing