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Final Exam for Computer Networking | CS 4457, Exams of Computer Systems Networking and Telecommunications

University of Virginia (UVA)Computer Systems Networking and Telecommunications
Prof. Kamin Whitehouse

Material Type: Exam; Professor: Whitehouse; Class: Computer Networks; Subject: Computer Science; University: University of Virginia; Term: Spring 2008;

Typology: Exams

Pre 2010

Uploaded on 03/09/2009

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Student ID: ___________________
CS457: Computer Networking
Date: 5/5/2008
Name: _______________________
Instructions:
1. Be sure that you have 10 questions
2. Write your Student ID (email) at the top of every page
3. Be sure to complete the honor statement after you complete the exam
4. This is a closed book exam
5. The seats on both sides of you should be empty
6. State all assumptions and be sure your answers are legible
7. Show all work; the graders will give partial credit
8. Answer each question clearly and to the point; do not define or describe concepts unless asked
to do so; assume that the graders are familiar with the concepts
Question Points Score
1 10
2 10
3 10
4 10
5 10
6 10
7 10
8 10
9 10
10 10
total 100
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Download Final Exam for Computer Networking | CS 4457 and more Exams Computer Systems Networking and Telecommunications in PDF only on Docsity!

CS457: Computer Networking Date: 5/5/ Name: _______________________ Instructions:

  1. Be sure that you have 10 questions
  2. Write your Student ID (email) at the top of every page
  3. Be sure to complete the honor statement after you complete the exam
  4. This is a closed book exam
  5. The seats on both sides of you should be empty
  6. State all assumptions and be sure your answers are legible
  7. Show all work; the graders will give partial credit
  8. Answer each question clearly and to the point; do not define or describe concepts unless asked to do so; assume that the graders are familiar with the concepts Question Points Score 1 10 2 10 3 10 4 10 5 10 6 10 7 10 8 10 9 10 10 10 total 100
  1. Answer the following True/False questions by circling either T or F.
    1. If a nonpersistent, nonpipelined connection takes 100 RTTs to retrieve a web page, a persistent, nonpipelined connection would take 25 RTTs for the same page. T F
    2. Iterative DNS queries require shorter socket connections with DNS servers than recursive DNS queries. T F
    3. A machine can open more than one TCP socket on the same port. T F
    4. TCP is fair because of additive increase/multiplicative decrease, not because of slow start. T F
    5. NAT can support more than 65535 simultaneous processes. T F
    6. BGP emphasizes policy and scalability over routing efficiency, sometimes producing lessthan optimal routes. T F
    7. Some error detection schemes are guaranteed to detect errors for any number of flipped bits in the packet. T F
    8. An entity's “certificate” is its public key encrypted by a certificate authority's private key. T F
    9. In CSMA/CD, a node always waits a random time before transmitting any packet. T F
    10. A maninthemiddle attack is more powerful with public key authentication than with symmetric key authentication. T F

16 total c. using TCP? A sends 6 + 4 = 10 messages B sends 2 + 4 = 6 acknowledgments 16 total

  1. Hubs, switches, and routers a. When MUST you use a switch instead of a hub? When the links to be connected have different bit rates. b. When MUST you use a router instead of a switch? When the links between the switches contain a cycle. c. Name the three basic types of switching fabrics used inside of a router.
    1. Memorybased
    2. Busbased
    3. Crossbar/ Banyan/interconnect networks d. Which of these are susceptible to headoftheline blocking? Only crossbar networks are susceptible to head of the line blocking, because the other two cannot simultaneously transfer packets from input to output ports anyway. e. Which of these are susceptible to output port queuing? All of these are susceptible to output port queuing.
  1. Routing a. Use Dijkstra's algorithm to find the shortest path D(i) and the previous node on that path p(i) from node u to all other nodes i in the network shown below. b. Convert this shortest path estimates calculated above into a routing table for u. See above.
  1. Wireless Media Access Control In the following diagram, nodes A, B, C, and D have circular radio range. Recall that a “collision” occurs when a receiver can hear a data packet from two different transmitters at the same time. a. Which pairs of nodes can transmit without causing a collision? A> B and D>C B> A and C>D b. Using CSMA/CA, which pairs of nodes can not transmit simultaneously, but would not cause a collision anyway if they did? What is the name of this problem? B> A and C>D “Exposed Terminal problem” c. Using CSMA/CA, which pairs of nodes can transmit simultaneously but would cause a collision? What is the name of this problem? A> B and C>D B> A and D>C “Hidden Terminal Problem” d. Using RTS/CTS, which pairs of nodes can not transmit simultaneously, but would not cause a

7. ARP

In the following diagram, assume that all nodes have been configured with the correct IP addresses, subnet, and default gateway router. However, all of their ARP tables are currently empty. a. Show all messages (including both IP and ARP messages) that must be sent/received in order to transfer a message from node A to node B.

  1. A sends ARP request for gateway physical address
  2. Gateway responds with ARP reply
  3. A sends message to gateway
  4. Gateway sends ARP request for B's physical address
  5. B responds with ARP reply
  6. Gateway forwards message to B b. How does each node decide whether to use the default gateway's physical address or that of the destination? Nodes will send all messages to their gateway routers, unless the destination is on the same subnet. In that case, nodes will send the message directly to the destination.
  1. Public Key Cryptography For public key cryptography, we would like to choose values e, d, and n such that: If we choose two values p and q to be prime such that pq = n, we can use the following number theory result to help in step 2 of the derivation below: What constraints do we need to introduce in steps 3 and 4 to make those steps correct? a. (e*d) mod ( p1 ) ( q1 ) = 1 b. m < n

10. CDMA

Assume that a CDMA receiver receives two simultaneous messages from different CSMA transmitters. The following values are read from the radio: 0 2 0 2 0 0 2 2 a. What bit value is the first transmitter sending if it is using the code: 1 1 1 1 1 1 1 1 1 b. What bit value is the second transmitter sending if it is using the code: 1 1 1 1 1 –1 1 1 1 Honor Code Signature