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141. Choose the false one.
a. Diffie – Hellman protocol is a symmetric key protocol
b. In RSA, both keys are private
c. DES is a block clipher algorithm
d. Vigenere clipher is poly-alphabetic in nature
Answer: (b).In RSA, both keys are private

142. There are 15 users communicating to each other. How many pairs of keys are required to authenticate the communications if the symmetric key is used?
a. 15
b. 30
c. 105
d. (15)²
Answer: (c).105

143. Consider a bandwidth of line 200mbps and sequence number field is 48-bits. Find out the wrap-around time of sequence numbers.
a. A
b. B
c. C
d. D
Answer: (c).C

144. Let the value of the RTT(Round-Trip-Time)is to be measure (d). The value of the previous RTT be 350μs. Let the value of α be 90% the new RTT, hence the retransmission time is ______ .(Assume it takes a segment at this moment to be acknowledged in 90μs)
a. 396, 796
b. 348, 696
c. 321, 644
d. 324, 648
Answer: (d).324, 648

145. Suppose a web server application generates messages consisting of 120 bytes if every second to the Central host, and each message gets encapsulated in a UDP segment and then an IPV4 Datagram. There are no options added in the TCP (or) Ip headers. What percentage of each Datagram will consist of data generated by the application?
a. 81%
b. 75%
c. 25%
d. 20%
Answer: (a).81%

146. Suppose that a TCP entity receives 2 MB file from the application layer and the IP layer is willing to Carry blocks of maximum size 1600 B; calculate the amount of overhead incurred from Segmenting the file into packet-sized units. Assume both TCP and Ip header of 20 B.
a. 10%
b. 2.6%
c. 2%
d. 17%
Answer: (b).2.6%