# Computer Networks (Test 3)

## Gate Exam : Cs Computer Science And Information Technology

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Computer Networks
| Computer Networks |
Q.1
Consider a source computer (S) transmitting a file of size 106 bits to a destination computer (D) over a network of two routers (R1 and R2) and three links (L1, L2, and L3). L1 connects S to R1; L2 connects R1 to R2; and L3 connects R2 to D. Let each link be of length 100km. Assume signals travel over each line at a speed of 108 meters per second. Assume that the link bandwidth on each link is 1Mbps. Let the file be broken down into 1000 packets each of size 1000 bits. Find the total sum of transmission and propagation delays in transmitting the file from S to D?
A. 1005ms
B. 1010ms
C. 3000ms
D. 3003ms
Explaination / Solution:
No Explaination.

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Q.2
A computer network uses polynomials over GF(2) for error checking with 8 bits as information bits and uses x3 + x + 1 as the generator polynomial to generate the check bits. In this network, the message 01011011 is transmitted as
A. 01011011010
B. 01011011011
C. 01011011101
D. 01011011100
Explaination / Solution:

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Q.3
An Internet Service Provider (ISP) has the following chunk of CIDR-based IP addresses available with it: 245.248.128.0/20. The ISP wants to give half of this chunk of addresses to Organization A, and a quarter to Organization B, while retaining the remaining with itself. Which of the following is a valid allocation of address to A and B?
A. 245.248.136.0/21 and 245.248.128.0/22
B. 245.248.128.0/21 and 245.248.128.0/22
C. 245.248.132.0/22 and 245.248.132.0/21
D. 245.248.136.0/24 and 245.248.132.0/21
Explaination / Solution:

Since half of 4096 host addresses must be given to organization A, we can set 12th bit to 1 and include that bit into network part of organization A, so the valid allocation of addresses to A is 245.248.136.0/21
Now for organization B, 12th bit is set to ‘0’ but since we need only half of 2048 addresses, 13th bit can be set to ‘0’ and include that bit into network part of organization B so the valid allocation of addresses to B is 245.248.128.0/22

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Q.4
One of the header fields in an IP datagram is the Time to Live (TTL) field. Which of the following statements best explains the need for this field?
A. It can be used to prioritize packets
B. It can be used to reduce delays
C. It can be used to optimize throughput
D. It can be used to prevent packet looping
Explaination / Solution:
No Explaination.

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Q.5
Which one of the following is not a client server application?
A. Internet chat
B. Web browsing
C. E-mail
D. Ping
Explaination / Solution:
No Explaination.

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Q.6
Which of the following concurrency control protocols ensure both conflict serializability and freedom from deadlock? I. 2-phase locking II. Time-stamp ordering
A. I only
B. II only
C. Both I and II
D. Neither I nor II
Explaination / Solution:
No Explaination.

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Q.7
What is the appropriate pairing of items in the two columns listing various activities encountered in a software li fe cycle?
P. Requirements Capture   1. Module Development and Integration
Q. Design                          2. Domain Analysis
R. Implementation             3. Structural and Behavioral Modeling
S. Maintenance                 4. Performance Tuning
A. P-3, Q-2,R-4,S-1
B. P-2, Q-3,R-1,S-4
C. P-3, Q-2,R-1,S-4
D. P-2, Q-3,R-4,S-1
Explaination / Solution:
No Explaination.

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Q.8
Assume that source S and destination D are connected through two intermediate routers labeled R. Determine how many times each packet has to visit the network layer and the data link layer during a transmission from S to D.

A. Network layer – 4 times and Data link layer-4 times
B. Network layer – 4 times and Data link layer-3 times
C. Network layer – 4 times and Data link layer-6 times
D. Network layer – 2 times and Data link layer-6 times
Explaination / Solution:

From above given diagram, its early visible that packet will visit network layer 4 times, once at each node [S, R, R, D] and packet will visit Data Link layer 6 times. One time at S and one time at D, then two times for each intermediate router R as data link layer is used for link to link communication.
Once at packet reaches R and goes up from physical –DL-Network and second time when packet coming out of router in order Network – DL- Physical

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Q.9
The transport layer protocols used for real time multimedia, file transfer, DNS and email, respectively are
A. TCP, UDP, UDP and TCP
B. UDP, TCP, TCP and UDP
C. UDP, TCP, UDP and TCP
D. TCP, UDP, TCP and UDP
Explaination / Solution:

Real time multimedia needs connectionless service, so under lying transport layer protocol used is UDP File transfer rums over TCP protocol with port no-21 DNS runs over UDP protocol within port no-53 Email needs SMTP protocol which runs over TCP protocol within port no – 25

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Q.10
A system has n resources R0,…,Rn-1, and k processes P0,…..Pk-1. The implementation of the resource request logic of each process Pi. is as follows:
if (i% 2==0) {
if (i<n) request Ri;
if (i+2<n)request Ri+2 ;
}
else {
if (i<n) request Rn-i ;
if (i+2<n)request Rn-i-2 ;
}
In which one of the following situations is a deadlock possible?
A. n = 40,k = 26
B. n = 21,k = 12
C. n = 20,k = 10
D. n = 41,k = 19