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Circuit Switching - Computer Netrwork - Exam, Exams of Computer Networks

Cochin University of Science and TechnologyComputer Networks

These are the Exam of Computer Network and its key important points are: Circuit Switching, Fundamental Measures, Circuit Switching, Packet Delay, Signal Propagation, Components, Stop-And-Wait Protocol, Packets, Retransmission, Time-Out

Typology: Exams

2012/2013

Uploaded on 03/28/2013

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Comprehensive Final Exam for Computer Networks Spring 2006
Name: ______________________________________
Welcome to the comprehensive final exam for Computer Networks. Read each problem carefully. There
are ten required problems each worth 10 points and one extra credit problem worth 10 points. You may
have with you a calculator, pencils, blank paper, lucky rabbit's foot, and one 8.5 x 11 inch “formula
sheet”. On this formula sheet you may have anything you want (definitions, formulas, homework
answers, old exam answers, etc.) as handwritten by you on both sides of the sheet. Photocopies, scans,
or computer generated text are not allowed on this sheet. You have 120 minutes for the exam. Unless
otherwise stated in the problem, start the answer for each new problem on a separate sheet of paper and
write only on one side of each sheet. Good luck and be sure to show your work!
Problem #1
Answer the following questions regarding the basics of computer networks and the Internet.
a) What are the fundamental measures of interest for a communications system?
b) Briefly describe circuit switching and packet switching.
c) What are the four causes of packet delay?
d) Roughly, what is the signal propagation delay from here to Atlanta (about 400 miles)?
e) Define the open concept.
Problem #2
Describe how email works. Describe the key components and flows. Identify key standards that apply.
Use figures as needed. About 150 words should be sufficient.
Problem #3
Attached are server.c and client.c with some “bugs”. Identify the bugs and explain how to fix
them.
Problem #4
Derive the formula for link utilization (U) for the stop-and-wait protocol. You may assume that a sender
always has packets to send and that packets are never lost or in error. If other assumptions are needed to
complete a reasonable derivation, state them.
pf3
pf4
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Partial preview of the text

Download Circuit Switching - Computer Netrwork - Exam and more Exams Computer Networks in PDF only on Docsity!

Comprehensive Final Exam for Computer Networks Spring 2006

Name: ______________________________________

Welcome to the comprehensive final exam for Computer Networks. Read each problem carefully. There

are ten required problems each worth 10 points and one extra credit problem worth 10 points. You may

have with you a calculator, pencils, blank paper, lucky rabbit's foot, and one 8.5 x 11 inch “formula

sheet”. On this formula sheet you may have anything you want (definitions, formulas, homework

answers, old exam answers, etc.) as handwritten by you on both sides of the sheet. Photocopies, scans,

or computer generated text are not allowed on this sheet. You have 120 minutes for the exam. Unless

otherwise stated in the problem, start the answer for each new problem on a separate sheet of paper and

write only on one side of each sheet. Good luck and be sure to show your work!

Problem

Answer the following questions regarding the basics of computer networks and the Internet.

a) What are the fundamental measures of interest for a communications system?

b) Briefly describe circuit switching and packet switching.

c) What are the four causes of packet delay?

d) Roughly, what is the signal propagation delay from here to Atlanta (about 400 miles)?

e) Define the open concept.

Problem

Describe how email works. Describe the key components and flows. Identify key standards that apply.

Use figures as needed. About 150 words should be sufficient.

Problem

Attached are server.c and client.c with some “bugs”. Identify the bugs and explain how to fix

them.

Problem

Derive the formula for link utilization ( U ) for the stop-and-wait protocol. You may assume that a sender

always has packets to send and that packets are never lost or in error. If other assumptions are needed to

complete a reasonable derivation, state them.

Problem

Answer the following questions about TCP:

a) Describe how TCP sets its retransmission time-out (RTO) value.

b) Show the packet flows for TCP connection establishment and termination.

Problem

Below are the first 60 bytes of a TCP/IP packet captured using Ethereal on an Ethernet network. On the

last pages of this exam are packet header templates. Decode the packet for the following fields:

  • Ethernet MAC source and destination addresses (hexadecimal)
  • IP source and destination addresses (in standard dotted-decimal format)
  • TCP source and destination port numbers (decimal)
  • Type of TCP segment (e.g., SYN, FIN, ACK, etc.)
  • Application layer protocol (and command, if applicable)

08 00 20 f7 88 7d 00 11 43 b7 92 43 08 00 45 00 .. ..}..C..C..E. 02 4b 1f f8 40 00 80 06 ca 9b 83 f7 03 2a 83 f7 .K..@........*.. 03 01 08 68 00 50 e0 5a 79 da 38 0b ef 53 50 18 ...h.P.Zy.8..SP. ff ff 80 d7 00 00 47 45 54 20 2f 7e 63 68 72 69 ......GET /~chri 73 74 65 6e 2f 63 68 72 69 73 74 65 6e 2e 68 74 sten/christen.ht 6d 6c 20 48 54 54 50 2f 31 2e 31 0d 0a 48 6f 73 ml HTTP/1.1..Hos

Problem

Answer the following questions about LANs (wired and wireless):

a) What is a LAN? Define it precisely.

b) Describe CSMA/CD and BEB as used in IEEE 802.3 Ethernet.

c) Describe CSMA/CA as used in IEEE 802.11 WiFi.

Problem

Answer the following questions bridges and switches:

a) What is a bridge? What is a switch? What are the motivations to use bridges and switches?

b) Describe (give) the forwarding and learning algorithm for transparent bridges.

c) What is “media speed” or “wire speed” (in packets per second) for 1500 byte packets on a 1 Gb/s

Ethernet link.

  1. //======================================================= file = server.c =====
  2. //= A message "server" program to demonstrate sockets programming =
  3. //= - TCP/IP client/server model is implemented =
  4. //=============================================================================
  5. //----- Include files ---------------------------------------------------------
  6. #include <stdio.h> // Needed for printf()
  7. #include <string.h> // Needed for memcpy() and strcpy()
  8. #include <windows.h> // Needed for all Winsock stuff
  9. //----- Defines ---------------------------------------------------------------
  10. #define PORT_NUM 1050 // Arbitrary port number for the server
  11. //===== Main program ==========================================================
  12. void main(void)
  13. {
  14. WORD wVersionRequested = MAKEWORD(1,1); // Stuff for WSA functions
  15. WSADATA wsaData; // Stuff for WSA functions
  16. unsigned int welcome_s; // Welcome socket descriptor
  17. struct sockaddr_in server_addr; // Server Internet address
  18. unsigned int connect_s; // Connection socket descriptor
  19. struct sockaddr_in client_addr; // Client Internet address
  20. struct in_addr client_ip_addr; // Client IP address
  21. int addr_len; // Internet address length
  22. char out_buf[100]; // Output buffer for data
  23. char in_buf[100]; // Input buffer for data
  24. // This stuff initializes winsock
  25. WSAStartup(wVersionRequested, &wsaData);
  26. // Fill-in server (my) address information and bind the welcome socket
  27. server_addr.sin_family = AF_INET;
  28. server_addr.sin_port = PORT_NUM;
  29. server_addr.sin_addr.s_addr = htonl(INADDR_ANY);
  30. // Listen on welcome socket for a connection
  31. listen(welcome_s, 0);
  32. // Accept a connection.
  33. connect_s = accept(welcome_s, (struct sockaddr *)&client_addr, &addr_len);
  34. // Print an informational message that accept completed
  35. printf("Accept completed \n”);
  36. // Send to the client using the connect socket
  37. strcpy(out_buf, "Test message from server to client");
  38. send(welcome_s, out_buf, strlen(out_buf), 0);
  39. // Receive from the client using the connect socket
  40. recv(welcome_s, in_buf, sizeof(in_buf), 0);
  41. printf("Received from client... data = '%s' \n", in_buf);
  42. // Close sockets and clean-up
  43. closesocket(connect_s);
  44. WSACleanup();
  45. }
  1. //======================================================= file = client.c =====
  2. //= A message "client" program to demonstrate sockets programming =
  3. //= - TCP/IP client/server model is implemented =
  4. //=============================================================================
  5. //----- Include files ---------------------------------------------------------
  6. #include <stdio.h> // Needed for printf()
  7. #include <string.h> // Needed for memcpy() and strcpy()
  8. #include <windows.h> // Needed for all Winsock stuff
  9. //----- Defines ---------------------------------------------------------------
  10. #define PORT_NUM 1050 // Port number used at the server
  11. #define IP_ADDR "127.0.0.1" // IP address of server (*** HARDWIRED ***)
  12. //===== Main program ==========================================================
  13. void main(void)
  14. {
  15. WORD wVersionRequested = MAKEWORD(1,1); // Stuff for WSA functions
  16. WSADATA wsaData; // Stuff for WSA functions
  17. unsigned int client_s; // Client socket descriptor
  18. double server_addr; // Server Internet address
  19. char out_buf[10]; // Output buffer for data
  20. char in_buf[10]; // Input buffer for data
  21. // This stuff initializes winsock
  22. WSAStartup(wVersionRequested, &wsaData);
  23. // Create a client socket
  24. client_s = socket(AF_INET, DATAGRAM, 0);
  25. // Fill-in the server's address information and do a connect with the
  26. // listening server
  27. server_addr.sin_family = AF_INET;
  28. server_addr.sin_port = PORT_NUM;
  29. server_addr.sin_addr.s_addr = inet_addr(IP_ADDR);
  30. connect(client_s, (struct sockaddr *)&server_addr, sizeof(server_addr));
  31. // Receive from the server using the client socket
  32. recv(client_s, in_buf, sizeof(in_buf), 0);
  33. printf("Received from server... data = '%s' \n", in_buf);
  34. // Send to the server using the client socket
  35. strcpy(out_buf, "Test message from client to server");
  36. send(client_s, out_buf, strlen(out_buf), 0);
  37. // Close and clean-up
  38. closesocket(client_s);
  39. WSACleanup();
  40. }

From: W. Stevens, TCP/IP Illustrated, Volume 1 The Protocols , Addison-Wesley, Boston, 1994.