C.S. 460 Computer Communications Final Examination
  1. Describe the major differences between Ipv4 and IPv6. How will the transition between V4 and V6 occur?
  2. Discuss ASN/BER encoding efficiency. What changes might be made to improve this efficiency? Contrast XDR and ASN.
  3. Describe the steps involved in calling procedure 0x55FB4 in program 0x55346 using SUN RPC.
  4. What must TCP do to guarantee reliable ordered delivery on top of an unreliable protocol(IP)?
  5. Describe the Split-Horizon and Split-Horizon with Poison Reverse heuristics used by RIP. Explain how they address the problem of routing loops.
  6. Given a graph similar to 6.11, identify the slow-start, linear increase and timeout periods as well as the Congestion Window and Congestion Threshold.  Indicate the changes that fast retransmit, TCP Vegas or RED would have on the graph.
  7. Assuming that you are using the version of TCP with window sizes much larger than 64kb. Suppose that you are using this extended TCP over a 1Gbps link with a latency of 100ms to transfer a 10MB file, and the TCP receive window is 1MB. If TCP sends 1KB packets, and assuming no congestion and no lost packets: How many RTTs does it take until the sender's congestion window reaches 1MB? (Recall that the congestion window is initialized to the size of a single packet) How many RTTs does it take to send the file? If the time to send the file is given by the number of required RTTs times the link latency, what is the effective throughput for the transfer? What percentage of the link bandwidth is utilized?
  8. What are the two main problems related to scalable routing on the internet and what techniques are used to combat these problems?
  9. Assume that you are using TCP over IPv6 to send a 1MB file. The file contains formatted data, so you are sending it 8 bytes at a time using xPush to flush unsent bytes after each send. If you are running over a 100Mbps line, how long will it take to send the file? What is your effective throughput?
  10. What are the differences between repeaters, bridges, switches, hubs and routers?
  11. What is DNS and what are the steps used to resolve the name alma.cs.byu.edu from the machine foo.ibm.com?
  12. Detail the SMTP protocol.  How reliable is the "MAIL FROM" field in determining the real source of an email message?
  13. What is the difference between flow control and congestion control and what mechanisms are used to implement each scheme?
  14. Why would you want to use UDP instead of TCP? Why would TCP be better?
  15. What are the differences between receiver-makes-right and canonical-intermediate-form and why would you want to use each of these methods?
  16. Use Run Length Encoding and Differential Pulse Code Modulation to encode the string AAAAAAAAAAAABBBAAAAAAABCBABC. Which scheme results in the highest compression? Assume that you can represent numbers with a given Huffman code and that characters take 8 bits.
  17. Describe three methods by which JPEG reduces the amount of data to be transmitted.
  18. Why does MPEG result in higher compression ratios than JPEG?  Given the DCT, quantization table, and Huffman code, show how a macroblock would be compressed using MPEG.
  19. What is motion compensation and what effect does it have on compression?
  20. What is the difference between DES and RSA encryption? Which scheme has provable bounds on the time necessary to break the encryption? Which scheme is public key vs secret key. How is RSA used in conjunction with MD5 in Keyed MD5? In which circumstances would you choose RSA, DES or MD5? Which services would you implement with each scheme?
  21. Given a small p and q, compute the public and private keys and USE RSA to encrypt and decrypt a message (something similar to page 579).
  22. Describe PEM message encryption and show the detailed steps of the algorithm.
  23. What are the advantages and disadvantages of DECbit vs RED in congestion control?
  24. How do RED gateways signal congestion? Why is this scheme preferred to the normal TCP congestion control scheme?
  25. Compare a filtering firewall to a proxy firewall in terms of protection against spoofing attacks (exercise 5.17).
  26. Contrast RIP, OSPF and BGP. Why are routers susceptible to attacks by hackers? What kinds of damage can occur in such an attack? What part the source routing requirement play in making attacks easier? How does the CIDR technique allow for more efficient use of IP address space?
  27. Assume that there is a maximum latency of 50ms for each bridge in the internetwork. What is the maximum time between when a IPv4 packet is sent and when it is received given that the maximum latency between bridges is 180ms (assume we have to go through a satellite on every link).
  28. What are the steps to setting up a UDP connection? How does this differ from a TCP connection?
  29. Describe the details of the DHCP protocol.  What are some of the reasons for DHCP?
  30. What is ICMP and how is it used with traceroute?
  31. Given a graph, show how a routing loop could occur with Distance Vector Routing.  Show how Split Horizon can help to solve this problem.
  32. Show how an LSP is floooded through a network.  At step 3, which nodes will be communicating, given a graph.
  33. Use Dijkstra's algorithm to compute the shortest path given a graph.
  34. How do the metrics differ for the original version of ARPANET and the second version of ARPANET?
  35. What are the SYN and ACK flags used for in TCP?  What is a SYN/ACK denial of service attack and how would it disturb the operation of the TCP protocol?
  36. What is the Karn/Partridge Algorithm and the Jacobson/Karels Algorithm?
  37. Would UDP or TCP be likely to achieve the highest bandwidth?  Why?
  38. What are the different approaches to fair queuing and which approaches are most effective and practical?
  39. Be able to compute Lempel Ziv compression for a set of data( http://www.data-compression.com/lossless.html)
  40. Could you use ARP to translate between a human readable name and an IP address? Why or Why not?
  41. Could you use DNS to translate between an IP address and an Ethernet address? Why or Why not?
  42.  
Created Feb 11, 1998
Updated Wed Apr 8 1998
(clement@cs.byu.edu)