CS560 Final Review

1
CS-560 Final Review
2
Administration

• All Late Work Due April 17
• If a significant part of your project was
  programming, give me a demo.
• Final Monday, April 23, 700am-1000am

3
Final Details

• Take Home
• Open Book
• Open Notes
• Open Mind
• Closed Internet

4
Potential Final Exam Questions

• What is the "power" metric and how is it used in
  network management?

5
Window Size

• What is the optimal window size for a 45Mbps
  connection over a 1000Km path with 10
  intermediate switches?

6
Flow Control

• Compare Forward Explicit Congestion Notification
  (FECN) to BECN. What are the advantages and
  disadvantages of each approach.
• Describe the three explicit congestion signaling
  approaches.
• Open Loop, Closed Loop, Absolute Peak
• Why will the Carried Load for a network with File
  Transfer applications be lower than the same
  network with Voice under Severe Congestion?

7
Flow Control

• What assumptions are made about the congestion
  interval in order for EFCI to work?
• What are the differences between Window-Based
  Congestion Control and Rate Based Congestion
  Control? Which is most effective at converging on
  a fair share configuration? Which is best at
  providing low delay and jitter?

8
Self Similarity

• What are 3 examples of self-similar traffic?
• What effect does self-similar traffic have on the
  network?
• Given a that your traffic has a Hurst parameter
  of 0.75, and utilization of 60, what are the
  buffer requirements (q)? What would the buffer
  requirements be assuming normal M/M/1 traffic.?
  What would the buffer requirements be for a fixed
  packet size network such as ATM (M/D/1)?
• Given a sequence of integers (representing
  bandwidth utilization) calculate several
  m-aggregated time series values and indicate the
  degree to which the sequence is self-similar.
• What is the Joseph Effect?

9
ARQ

• What are the differences between Go-back-N and
  Selective ARQ? Given a 50ms RTT on a OC-3c
  connection with 1500 byte frames, what is the
  normalized throughput given that the probability
  of errors is 0.001? What is the normalized
  throughput for Selective reject for this same
  situation with a window size of 10 frames? What
  is the normalized throughput for Go-back-N under
  the same assumptions?
• What is the silly window syndrome? How can you
  fix it?
• How does Jacobsons Algorithm improve TCP
  Performance? What is Karns Algorithm?

10
UBR ATM

• What problems occur when encapsulating TCP
  traffic over UBR ATM? Assume that you are using
  a 9180 octet TCP segment over UBR ATM and you
  have a cell loss rate of .004. You are running
  on a OC-3c line, what is your effective
  throughput? Describe two methods for improving
  the performance of TCP over UBR ATM.
• 9180/48191cells/TCP segment
• P(at least one lost) 1-P(none lost)
• 1-.9961911-.46.53 or 53 of the time, one cell
  will be lost, resulting in the retransmission of
  the whole segment

11
TCP/IP over AAL5
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Buffer Layout for Selective Drop
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Comparison
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Congestion Control

• Why would you want to use the flow label from
  IPV6 instead of identifying a flow by the IP
  address and TCP port?
• What is RSVP? How does it differ from TCP
  congestion control?
• What are 4 techniques that ISA uses to manage
  congestion?
• Admission Control (RSVP), Routing Algorithm
  (OSPF), Queuing discipline (WFQ), Discard Policy
  (RED)

15
Token Bucket

• Given a token bucket with size 250KB and a token
  arrival rate of 2MB/sec, how long can the flow
  transmit at the maximum rate of 25MB/s?
• What are the pros and cons of using WFQ vs FIFO?

16
Service Provisioning

• Consider a network with a single link modeled by
  an exponential server with a service time of 1
  second. Assume that you have two classes of
  traffic arriving at the server with arrival rates
  of 1 every 4 seconds for each class of traffic.
  Assume that traffic class 1 is VBR traffic and is
  paying more for the connection if the delay is
  low. The amount paid is U14-2(delay). The
  other traffic source is less sensitive to delay
  and is willing to pay U24-delay. Implementing
  prioritization in your server will add 25 to the
  cost of your service. Is it worth implementing
  two priorities?

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Traffic Descriptors

• What are the 4 elements considered in the Source
  Traffic Descriptor?
• What two issues are considered in the Traffic
  descriptor? What is the difference between CDVT
  and CDV?
• What is the difference between traffic shaping
  and traffic policing?

18
Assorted Topics

• Describe how you could send voice traffic with
  two different priorities in order to tolerate
  congestion.
• How is DNS used to implement load balancing for
  web servers?
• Assume ATM or IP as backbone, what are the
  implications of the choice in terms of providing
  QoS?
• Describe Dijkstra's algorithm and Bellman Ford. 
  Why would you want to use one over the other for
  routing and admission control?  What are the
  differences in complexity?
• What are the design goals of RED and how does the
  implementation accomplish these goals?