Computer Networks

Q31. In a packet switching network, packets are routed from source to destination along a single path having two intermediate nodes. If the message size is 24 bytes and each packet contains a header of 3 bytes, then the optimum packet size is(Gate 2005)

1. 4
2. 6
3. 7
4. 9
5.  

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Q32. An organization has a class B network and wishes to form subnets for 64 departments. The subnet mask would be(Gate 2005)

1. 255.255.0.0
2. 255.255.64.0
3. 255.255.128.0
4. 255.255.255.0

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Q33. In a network of LANs connected by bridges, packets are sent from one LAN to another through intermediate bridges. Since more than one path may exist between two LANs, packets may have to be routed through multiple bridges. Why is the spanning tree algorithm used for bridge routing? (Gate 2005)

1. For shortest path routing between LANs
2. For avoiding loops in the routing paths
3. For fault tolerance
4. For minimizing collisions

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Q34. The maximum window size for data transmission using the selective reject protocol with n-bit frame sequence numbers is (Gate 2005)

1. 2ⁿ
2. 2ⁿ⁻¹
3. 2ⁿ − 1
4. 2ⁿ⁻²

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Q35. The address resolution protoc0l (ARP) is used for (Gate 2005)

1. Finding the IP address from the DNS
2. Finding the IP address of the default gateway
3. Finding the IP address that corresponds to a MAC address
4. Finding the MAC address that corresponds to an IP address

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Q36. Packets of the same session may be routed through different paths in(Gate 2005)

1. TCP, but not UDP
2. TCP and UDP
3. UDP but not TCP
4. Neither TCP nor UDP

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Solve the problems and choose the correct answers.
Consider three IP networks A, B, and C. Host HA in network A sends messages each containing 180 bytes of application data to a host HC in network C. The TCP layer prefixes a 20-byte header to the message. This passes through an intermediate network B. The maximum packet size, including 20 byte IP header, in each network, is
A: 1000 bytes
B: 100 bytes
C: 1000 bytes
The Networks A and B are connected through a 1 Mbps link, while B and C are connected by a 512 Kbps link (bps=bits per second).

Question 37 and 38 are based on the above statement 

Q37.Assuming that the packets are correctly delivered, how many bytes, including headers, are delivered to the IP layer at the destination for one application message, in the best case? Consider only data packets.(Gate 2004)

1. 200
2. 220
3. 240
4. 260

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Q38. What is the rate at which application data is transferred to host Hc? Ignore errors, acknowledgments, and other overheads.(Gate 2004)

1. 325.5 Kbps
2. 354.5 Kbps
3. 409.6 Kbps
4. 512.0 Kpps

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Q39. The routing table of a router is shown below :

Destination	Subnet Mask	Interface
128.75.43.0	255.255.255.0	Eth 0
128.75.43.0	255.255.255.128	Eth 1
192.12.17.5	255.255.255.255	Eth 3
default		Eth 2

On which interface will the router forward packets addressed to destinations 128.75.43.16 and 192.12.17.10 respectively? (Gate 2004)

1. Eth 1 and Eth 2
2. Eth 0 and Eth 2
3. Eth 0 and Eth 3
4. Eth 1 and Eth 3

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Q40. A and B are the only two stations on an Ethernet. Each has a steady queue of frames to send. Both A and B attempt to transmit a frame, collide and A wins the first backoff race, At the end of this successful transmission by A, both A and B attempt to transmit and collide. The probability that A wins the second backoff race is(Gate 2004)

1. 0.5
2. 0.625
3. 0.75
4. 1.0

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