COMPUTER NETWORKING NUMERICAL QUESTION ANSWERS FOR GATE NET COMPUTER SCIENCE

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1. The maximum window size for data transmission using the selective reject protocol with n-bit frame sequence numbers is

 
 
 
 

2. Host A is sending data to host B over a full duplex link. A and B are using the sliding window protocol for flow control. The sender and receiver window sizes are 5 packets each. Data packets (sent only from A to B) are all 1000 bytes long and the transmission time for such a packet is 50ms. Acknowledgement packets (sent only from B to A) are very small and require negligible transmission time. The propagation delay over the link is 200 ms. What i the maximum achievable throughput in this communication?

 
 
 
 

3. Station A uses 32 byte packets to transmit messages to Station B using a sliding window protocol. The round trip time delay between A and B is 80 ms and the bottleneck bandwidth on the path A and B is 128kbps. What is the optimal window size that A should use?

 
 
 
 

4. The distance between two stations M and N is L kilometers. All frames are K bits long. The propagation delay per kilometer is t seconds. Let R bits/second be the channel capacity. Assuming that processing delay is negligible, the minimum number of bits for the sequence number field in a frame for maximum utilization, when the sliding window protocol is used, is:

 
 
 
 

5. The transport layer protocols used for real time multimedia, file transfer, DNS and email, respectively are

 
 
 
 

6. The subnet mask for a particular network is 255.255.31.0. Which of the following pairs of IP addresses could belong to this network.

 
 
 
 

7. The routing table of a router is shown below

DESTINATION SUBNETMASK ETHERNET
128.75.43.0 255.255.255.0 Eth0
128.75.43.0 255.255.255.128 Eth1
192.12.17.5 255.255.255.255 Eth3
Default Eth2

On which interface will router forward packets addressed to destinations 128.75.43.16 and 192.12.17.10 respectively?

 
 
 
 

8. 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?

 
 
 
 

9. Suppose computers A and B have IP addresses 10.105.1.113 and 10.105.1.91 respectively and they both use the same netmask N. Which of the values of N given below should not be used if A and B should belong to the same network?

 
 
 
 

10. Consider an instance of TCP’s Additive Increase Multiplicative Decrease(AIMD) algorithm where the window size at the start of the slow start phase is 2 MSS and the threshold at the start of the first transmission is 8 MSS. Assume that a time out occurs during the fifth transmission. Find the congestion window size at the end of the tenth transmission.

 
 
 
 

11. If a class B network on the Internet has a subnet mask of 255.255.248.0, what is the maximum number of hosts per subnet?

 
 
 
 

12. What is the maximum size of data that the application layer can pass on to the TCP layer below?

 
 
 
 

13. In the IPv4 addressing format, the number of networks allowed under Class C addresses is

 
 
 
 

14. An organization has a class B network and wishes to form subnets for 64 departments. The subnet mask would be:

 
 
 
 

15. 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.

 
 
 
 


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