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2012-08-21 12:05:45
netmg Tutorial

Network Management Tutorial 10
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  1. Traffic classification can be in the form of a Multi-Field (MF) or Behavior Aggregate (BA) classifier. How would the two be implemented at a network node?
    A MF classifier would use packet matching technique such as ACL. A BA classifier will match the DSCP value in the DS field.
  2. A simple model of a queuing system consists of queues and a scheduler. What are queues and scheduler?
    A queue is a data structure that holds packets that are awaiting transmission. A scheduler is a mechanism for selecting the next packet in the queue for transmission.
  3. A video stream needs half the bandwidth of T1. Explain how performance will be degraded if Weighted Fair Queuing (WFQ) is used and more flows are added.
    A video stream that needs half the bandwidth of T1 will be provided that by WFQ if there are two flows. As more flows are added, the video stream gets less of the bandwidth because WFQ's mechanism creates Fairness. If there are 10 flows, the video stream will get only 1/10th of the bandwidth, which is not enough.
  4. A video stream needs half the bandwidth of T1. Explain how a network administrator can use Class Based Weighted Fair Queuing (CBWFQ) to prevent multiple low-priority flows from swamping out a single high-priority flow reserved for the video stream.
    CBWFQ provides this. The network administrator defines a class, places the video stream in the class, and tells the router to provide the minimum bandwidth for the class. Video is now given the bandwidth that it needs. A default class is used for the rest of the flow. This class is serviced using flow0based WFQ schemes allocating the remainder of the bandwidth (half the TL, in this example).
  5. What is the difference between tail drop and active queue management?
    Tail drop is a simple form of queue management where new packets that arrive to a full queue are dropped.

    Active queue management such as RED (random early detection), drops packet before a queue becomes full. The rationale is that an aggressive flow will represent most of the arriving traffic and therefore it is likely that a RED will drop a packet of an aggressive session.
  6. How do policer and shaper respond to violations?
    A policer typically will either drop packet or rewrite its DSCP value to one with a higher drop precedence (For example from AF31 to AF32).

    A shaper typically delays excess traffic using a buffer, or queuing mechanism, to hold packets and shape the flow when the data rate of the source is higher than expected.
  7. Recommended Prioritization Schemes for Voice Traffic
    LLQ with maximum bandwidth of 48kbps
  8. Recommended Prioritization Schemes for Video Conferencing Traffic @ 384kpbs
    LLQ with maximum bandwidth of 460kbps
  9. Recommended Prioritization Schemes for Streaming Video Traffic @ 384kpbs
    CBWFQ with minimum bandwidth of 384 kbps
  10. Recommended Prioritization Schemes for Mission Critical Application @ 460 kbps
    CBWFQ with minimum bandwidth of 460kbps
  11. Recommended Prioritization Schemes for Other Traffic
    FIFO or WFQ