CS422: Fall2004 Final Exam

 

Name:___________________________________________

 

Question

Max.

Current

Part I. True and False

10 pts.

 

1-7

28 pts

 

8-15

32 pts

 

16-22

30 pts.

 

Total:

100pts

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Part 1. Answer True or False (1 point each)

___ Vector Distance Routing uses Dijkstra's Shortest Path algorithm to compute the best routes.
___ Routers may have multiple IP addresses but hosts should have only one IP address.
___ The maximum IP header size is 64 bytes.
___ 192.5.48.3 is a class C address.
___ ARP requests could be unicasted.
___ A host could fragment a large IP packet if it is larger than the MTU of the network.
___ After a packet is dropped due to a TTL=0 a router will send a ICMP "destination unreachable" to the source.
___ The size of the basic IP header is 20 bytes.
___ It is possible to send an ARP request to a remote network.
___ A packet fragment can be fragmented.

Part 2. Short Questions: (4 points each)

1. Explain what is the use of the TTL field in the IP packets, the most common initial value, and when the TTL is modified.

 

 

 

2. What parameters does a computer need to have when it is connected to the Internet.

 

 

 

3. Explain how ARP works.





 

4. Explain why routers do not send ICMP messages about other ICMP messages and explain a situation when an ICMP packet could cause another ICMP packet to be sent.

 

 

 

5. Assume a packet with ID=101 of length 1000 bytes is fragmented by a router when the next network has an MTU=400. Ignoring the size of the headers, give the values of the ID, length, MF flag,  and offset of each of the fragments.

 

 

 

 

6. Explain why UDP is considered a transport protocol.

 

 

 

7. Explain how path MTU discovery works and in what situations it may not work.

 

 

 

8. Explain how TCP deals with network congestion step by step.

 

 

 

9. What problems do you see having a retransmission timer with a fixed timeout.

 

 

 

10. Explain how adaptive retransmission works in TCP.

 

 

 

 

11. Explain why TCP  by default waits about 5 minutes to reuse a port number that has been previously used.

 

 

 

12. Explain what is a positive acknowledgment  and what is a negative acknowledgement.

 

 

 

 

13. Explain how a reliable protocol with negative acknowledgements could be implemented.

 

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14. Explain why the routers do not do reassembly?

 

 

 


15. Explain why in the three-way hand shake during closing a connection, 4 packets are necessary instead of three that are used during opening a connection.

 

 

 

16. Explain how NAT works.

 

 

 

 

17. Explain how VPN works

 

 

 

 

18. Assume that TCP will be used to communicate the earth with space ships doing exploration where transmission delays will be in the order of minutes.. Mention what modifications will be needed toTCP.

 

 

 

 


19. Explain what will happen if  you use TCP to send voice data in your internet phone.








20. Describe the function of the jitter buffer.









21. (5 pts.) Describe the use of the callNumber and the sampleOffset in the UDP packet of the Internet Phone.








22. (5 pts.) In your Internet Phone, how would do you compute the number of voice packets lost and the number of voice packets received too late.