GATE CSE topic:computer-networks PYQs & Answers — Page 5

Questions 41–50 of 72. Imported answers require independent review unless marked reviewed.

Consider a network with three routers P, Q, R shown in the figure below. All the links have cost of unity.

Diagram for Computer Science and Information Technology question 57

The routers exchange distance vector routing information and have converged on the routing tables, after which the link Q–R fails. Assume that P and Q send out routing updates at random times, at the same average rate. The probability of a routing loop forming (rounded off to one decimal place) between P and Q, leading to count-to-infinity problem, is __________.

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Consider a 100 Mbps link between an earth station (sender) and a satellite (receiver) at an altitude of 2100 km. The signal propagates at a speed of

m/s. The time taken (in milliseconds, rounded off to two decimal places) for the receiver to completely receive a packet of 1000 bytes transmitted by the sender is __________.

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Consider the data transfer using TCP over a 1 Gbps link. Assuming that the maximum segment lifetime (MSL) is set to 60 seconds, the minimum number of bits required for the sequence number field of the TCP header, to prevent the sequence number space from wrapping around during the MSL is __________.

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Consider the three-way handshake mechanism followed during TCP connection establishment between hosts P and Q. Let X and Y be two random 32-bit starting sequence numbers chosen by P and Q respectively. Suppose P sends a TCP connection request message to Q with a TCP segment having SYN bit = 1, SEQ number = X, and ACK bit = 0. Suppose Q accepts the connection request. Which one of the following choices represents the information present in the TCP segment header that is sent by Q to P?

Your answerChoose one option.

SYN bit = 1, SEQ number = X+1, ACK bit = 0, ACK number = Y, FIN bit = 0

SYN bit = 0, SEQ number = X+1, ACK bit = 0, ACK number = Y, FIN bit = 1

SYN bit = 1, SEQ number = Y, ACK bit = 1, ACK number = X+1, FIN bit = 0

SYN bit = 1, SEQ number = Y, ACK bit = 1, ACK number = X, FIN bit = 0

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Consider the following two statements.

: Destination MAC address of an ARP reply is a broadcast address.

: Destination MAC address of an ARP request is a broadcast address.

Which one of the following choices is correct?

Your answerChoose one option.

Both

and

are true.

is true and

is false.

is false and

is true.

Both

and

are false.

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A TCP server application is programmed to listen on port number

on host

. A TCP client is connected to the TCP server over the network. Consider that while the TCP connection was active, the server machine

crashed and rebooted. Assume that the client does not use the TCP keepalive timer. Which of the following behaviors is/are possible?

Your answerSelect all correct options. You can choose more than one.

If the client was waiting to receive a packet, it may wait indefinitely.

The TCP server application on

can listen on

after reboot.

If the client sends a packet after the server reboot, it will receive a RST segment.

If the client sends a packet after the server reboot, it will receive a FIN segment.

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Consider two hosts

and

connected through a router

. The maximum transfer unit (MTU) value of the link between

and

is 1500 bytes, and between

and

is 820 bytes. A TCP segment of size 1400 bytes was transferred from

through

, with IP identification value as 0x1234. Assume that the IP header size is 20 bytes. Further, the packet is allowed to be fragmented, i.e., Don’t Fragment (DF) flag in the IP header is not set by

. Which of the following statements is/are correct?

Your answerSelect all correct options. You can choose more than one.

Two fragments are created at

and the IP datagram size carrying the second fragment is 620 bytes.

If the second fragment is lost,

will resend the fragment with the IP identification value 0x1234.

If the second fragment is lost,

is required to resend the whole TCP segment.

TCP destination port can be determined by analysing only the second fragment.

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Consider a computer network using the distance vector routing algorithm in its network layer. The partial topology of the network is as shown below.

Diagram for Computer Science and Information Technology question 45

The objective is to find the shortest-cost path from the router

to routers

and

. Assume that

does not initially know the shortest routes to

and

. Assume that

has three neighboring routers denoted as

, and

. During one iteration,

measures its distance to its neighbours

, and

as 3, 2, and 5, respectively. Router

gets routing vectors from its neighbours that indicate that the distance to router

from routers

, and

are 7, 6, and 5, respectively. The routing vector also indicates that the distance to router

from routers

, and

are 4, 6, and 8, respectively. Which of the following statement(s) is/are correct with respect to the new routing table of

, after update during this iteration?

Your answerSelect all correct options. You can choose more than one.

The distance from

will be stored as 10.

The distance from

will be stored as 7.

The next hop router for a packet from

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Consider the sliding window flow-control protocol operating between a sender and a receiver over a full-duplex error-free link. Assume the following:

The time taken for processing the data frame by the receiver is negligible.

The time taken for processing the acknowledgement frame by the sender is negligible.

The sender has infinite number of frames available for transmission.

The size of the data frame is 2,000 bits and the size of the acknowledgement frame is 10 bits.

The link data rate in each direction is 1 Mbps (=

bits per second).

One way propagation delay of the link is 100 milliseconds.

The minimum value of the sender’s window size in terms of the number of frames (rounded to the nearest integer) needed to achieve a link utilization of 50% is __________.

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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 (=

bits per second). The aggregate number of transmissions across all the nodes (including new frame transmissions and retransmitted frames due to collisions) is modeled 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 ____________.

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GATE CSE topic:computer-networks PYQs

Question 57

Question 59

Question 60

Question 7

Question 8

Question 44

Question 45

Question 45

Question 49

Question 54