GATE IT 2006

Question 61

Consider the following XML DTD describing course information in a university:

XML

<!ELEMENT Univ (Course+, Prof+)>
<!ELEMENT Course (Title, Eval*)>
<!ATTLIST Course Number ID #REQUIRED Instructor IDREF #IMPLIED>
<!ELEMENT Title (#PCDATA)>
<!ELEMENT Eval (#PCDATA)>
<!ATTLIST Eval Score CDATA #REQUIRED>
<!ELEMENT Prof EMPTY>
<!ATTLIST Prof Name ID #REQUIRED Teaches IDREF #IMPLIED>

What is returned by the following XQuery? let $as := / /@Score
for $c in /Univ/Course[Eval]
let $cs := $c/Eval?@Score
where min($cs) > avg($as)
return $c

• The professor with the lowest course evaluation
• Professors who have all their course evaluations above the university average
• The course with the lowest evaluation
• Courses with all evaluations above the university average

Question 62

A router uses the following routing table:

A packet bearing a destination address 144.16.68.117 arrives at the router. On which interface will it be forwarded?

• eth0
• eth1
• eth2
• eth3

Question 63

Suppose that it takes 1 unit of time to transmit a packet (of fixed size) on a communication link. The link layer uses a window flow control protocol with a window size of N packets. Each packet causes an ack or a nak to be generated by the receiver, and ack/nak transmission times are negligible. Further, the round trip time on the link is equal to N units. Consider time i > N. If only acks have been received till time i(no naks), then the goodput evaluated at the transmitter at time i(in packets per unit time) is

• 1 - N/i
• i/(N + i)
• 1
• 1 - e^(i/N)

Question 64

In the 4B/5B encoding scheme, every 4 bits of data are encoded in a 5-bit codeword. It is required that the codewords have at most 1 leading and at most 1 trailing zero. How many such codewords are possible?

• 14
• 16
• 18
• 20

Question 65

A router has two full-duplex Ethernet interfaces each operating at 100 Mb/s. Ethernet frames are at least 84 bytes long (including the Preamble and the Inter-Packet-Gap). The maximum packet processing time at the router for wirespeed forwarding to be possible is (in micro­seconds)

• 0.01
• 3.36
• 6.72
• 8

Question 66

A link of capacity 100 Mbps is carrying traffic from a number of sources. Each source generates an on-off traffic stream; when the source is on, the rate of traffic is 10 Mbps, and when the source is off, the rate of traffic is zero. The duty cycle, which is the ratio of on-time to off-time, is 1 : 2. When there is no buffer at the link, the minimum number of sources that can be multiplexed on the link so that link capacity is not wasted and no data loss occurs is S₁. Assuming that all sources are synchronized and that the link is provided with a large buffer, the maximum number of sources that can be multiplexed so that no data loss occurs is S₂. The values of S₁ and S₂ are, respectively,

• 10 and 30
• 12 and 25
• 5 and 33
• 15 and 22

Question 67

On a wireless link, the probability of packet error is 0.2. A stop-and-wait protocol is used to transfer data across the link. The channel condition is assumed to be independent from transmission to transmission. What is the average number of transmission attempts required to transfer 100 packets?

• 100
• 125
• 150
• 200

Question 68

A program on machine X attempts to open a UDP connection to port 5376 on a machine Y, and a TCP connection to port 8632 on machine Z. However, there are no applications listening at the corresponding ports on Y and Z. An ICMP Port Unreachable error will be generated by

• Y but not Z
• Z but not Y
• Neither Y nor Z
• Both Y and Z

Question 69

A subnetted Class B network has the following broadcast address : 144.16.95.255. Its subnet mask

• is necessarily 255.255.224.0

• is necessarily 255.255.240.0

• is necessarily 255.255.248.0

• could be any one of 255.255.224.0, 255.255.240.0, 255.255.248.0

Question 70

An array X of n distinct integers is interpreted as a complete binary tree. The index of the first element of the array is 0. The index of the parent of element X[i],i≠0 is?

• lowerbound[i/2]
• upperbound[(i-1)/2]
• upperbound[i/2]
• upperbound[i/2] -1