50 Computer Networks MCQs with Answers

Question 1

Consider a network using the pure ALOHA medium access control protocol, where each frame is of length 1,000 bits. The channel transmission rate is 1 Mbps (=10⁶ bits per second). The aggregate number of transmissions across all the nodes (including new frame transmissions and retransmitted frames due to collisions) is modelled as a Poisson process with a rate of 1,000 frames per second. Throughput is defined as the average number of frames successfully transmitted per second. The throughput of the network (rounded to the nearest integer) is ______________ .

• 130 to 140
• 140 to 150
• 120 to 130
• 100 to 110

Question 2

Consider the cyclic redundancy check (CRC) based error detecting scheme having the generator polynomial X³+X+1. Suppose the message m₄m₃m₂m₁m₀ = 11000 is to be transmitted. Check bits c₂c₁c₀ are appended at the end of the message by the transmitter using the above CRC scheme. The transmitted bit string is denoted by m₄m₃m₂m₁m₀c₂c₁c₀. The value of the checkbit sequence c₂c₁c₀ is

• 101
• 110
• 100
• 111

Question 3

Consider a link with packet loss probability of 0.2. What is the expected number of transmissions it would take to transfer 200 packets given that the stop and wait protocol is used?

• 125
• 250
• 225
• 150

Question 4

Assume that Source S and Destination D are connected through an intermediate router R. How many times a packet has to visit the network layer and data link layer during a transmission from S to D?

• Network layer – 4 times, Data link layer – 4 times
• Network layer – 4 times, Data link layer – 6 times
• Network layer – 2 times, Data link layer – 4 times
• Network layer – 3 times, Data link layer – 4 times

Question 5

An Ethernet frame that is less than the IEEE 802.3 minimum length of 64 octets is called

• Short frame

• Small frame

• Mini frame

• Runt frame

Question 6

Which of the following protocols is an application layer protocol that establishes, manages and terminates multimedia sessions ?

• Session Maintenance Protocol
• Real - time Streaming Protocol
• Real - time Transport Control Protocol
• Session Initiation Protocol

Question 7

What is the size of the ‘total length’ field in IPv₄ datagram?

• 4 bit
• 8 bit
• 16 bit
• 32 bit

Question 8

A packet filtering firewall can

• deny certain users from accessing a service
• block worms and viruses from entering the network
• disallow some files from being accessed through FTP
• block some hosts from accessing the network

Question 9

Consider the set of activities related to e-mail A : Send an e-mail from a mail client to mail server B : Download e-mail headers from mail box and retrieve mails from server to a cache C : Checking e-mail through a web browser The application level protocol used for each activity in the same sequence is

• SMTP, HTTPS, IMAP
• SMTP, POP, IMAP
• SMTP, IMAP, HTTPS
• SMTP, IMAP, POP

Question 10

What is one advantage of setting up a DMZ(Demilitarized Zone) with two firewalls?

• You can control where traffic goes in the three networks

• You can do stateful packet filtering

• You can do load balancing

• Improve network performance