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Computer Networks (CN)

GATE-2019

Q:   Which of the following protocol pairs can be used to send and retrieve e-mails (in that order)?

  • A:  IMAP, POP3
  • B:  SMTP, POP3
  • C:  SMTP, MIME
  • D:  IMAP, SMTP
GATE-2019

Q:   Consider three machines M, N, and P with IP addresses 100.10.5.2, 100.10.5.5, and 100.10.5.6 respectively. The subnet mask is set to 255.255.255.252 for all the three machines. Which one of the following is true? ________.

  • A:  M, N, and P all belong to the same subnet
  • B:  Only M and N belong to the same subnet
  • C:  Only N and P belong to the same subnet
  • D:  M, N, and P belong to three different subnets
GATE-2019

Q:   Suppose that in an IP-over-Ethernet network, a machine X wishes to find the MAC address of another machine Y in its subnet. Which one of the following techniques can be used for this?

  • A:  X sends an ARP request packet to the local gateway’s IP address which then finds the MAC address of Y and sends to X
  • B:  X sends an ARP request packet to the local gateway’s MAC address which then finds the MAC address of Y and sends to X
  • C:  X sends an ARP request packet with broadcast MAC address in its local subnet
  • D:  X sends an ARP request packet with broadcast IP address in its local subnet
GATE-2019

Q:   Consider that 15 machines need to be connected in a LAN using 8-port Ethernet switches. Assume that these switches do not have any separate uplink ports. The minimum number of switches needed is__________.

GATE-2019

Q:   In an RSA cryptosystem, the value of the public modulus parameter n is 3007. If it is also known that φ(n)=2880, where φ() denotes Euler’s Totient Function, then the prime factor of n which is greater than 50 is ____________________.
GATE-2018

Q:   Consider the following statements regarding the slow start phase of the TCP congestion control algorithm. Note that cwnd stands for the TCP congestion window and MSS denotes the Maximum Segment Size.
(i) The cwnd increases by 2 MSS on every successful acknowledgment.
(ii) The cwnd approximately doubles on every successful acknowledgement.
(iii) The cwnd increases by 1 MSS every round trip time.
(iv) The cwnd approximately doubles every round trip time.
Which one of the following is correct?

  • A:  Only (ii) and (iii) are true
  • B:  Only (i) and (iii) are true
  • C:  Only (iv) is true
  • D:  Only (i) and (iv) are true
GATE-2018

Q:   Consider a long-lived TCP session with an end-to-end bandwidth of 1 Gbps (= 109 bits-persecond). The session starts with a sequence number of 1234. The minimum time (in seconds, rounded to the closest integer) before this sequence number can be used again is _______.

GATE-2018

Q:   Consider an IP packet with a length of 4,500 bytes that includes a 20-byte IPv4 header and a 40-byte TCP header. The packet is forwarded to an IPv4 router that supports a Maximum Transmission Unit (MTU) of 600 bytes. Assume that the length of the IP header in all the outgoing fragments of this packet is 20 bytes. Assume that the fragmentation offset value stored in the first fragment is 0.
The fragmentation offset value stored in the third fragment is _______.

GATE-2018

Q:   Consider a simple communication system where multiple nodes are connected by a shared broadcast medium (like Ethernet or wireless). The nodes in the system use the following carrier-sense based medium access protocol. A node that receives a packet to transmit will carrier-sense the medium for 5 units of time. If the node does not detect any other transmission in this duration, it starts transmitting its packet in the next time unit. If the node detects another transmission, it waits until this other transmission finishes, and then begins to carrier-sense for 5 time units again. Once they start to transmit, nodes do not perform any collision detection and continue transmission even if a collision occurs. All transmissions last for 20 units of time. Assume that the transmission signal travels at the speed of 10 meters per unit time in the medium.
Assume that the system has two nodes P and Q, located at a distance d meters from each other. P starts transmitting a packet at time t=0 after successfully completing its carrier-sense phase. Node Q has a packet to transmit at time t=0 and begins to carrier-sense the medium.
The maximum distance d (in meters, rounded to the closest integer) that allows Q to successfully avoid a collision between its proposed transmission and P’s ongoing transmission is _____.

GATE-2017

Q:   Consider a TCP client and a TCP server running on two different machines. After completing data transfer, the TCP client calls close to terminate the connection and a FIN segment is sent to the TCP server. Server-side TCP responds by sending an ACK, which is received by the client-side TCP. As per the TCP connection state diagram (RFC 793), in which state does the client-side TCP connection wait for the FIN from the server-side TCP?

  • A:  LAST-ACK
  • B:  TIME-WAIT
  • C:  FIN-WAIT-1
  • D:  FIN-WAIT-2
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