Solutions

1
Tutorial 6

• Solutions

2
Q.1

• Suppose that the WFQ scheduling policy is applied
  to a buffer that supports three classes, and
  suppose the weights are 0.5, 0.25, and 0.25 for
  the three classes. Suppose that each class has a
  large number of packets in the buffer. In what
  sequence might the three classes be served in
  order to achieve the WFQ weights?
• Suppose that classes 1 and 2 have a large number
  of packets in the buffer and there are no class 3
  packets in the buffer. In what sequence might the
  three classes be served in to achieve the WFQ
  weights?

3
Scheduling Policies still more

• Weighted Fair Queuing
• generalized Round Robin
• each class gets weighted amount of service in
  each cycle

4
Question 1

• a) One possible sequence is 1 2 1 3 1 2 1 3 1 2 1
  3
• b) 1 1 2 1 1 2 1 1 2 1 1 2

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Q.2

• Consider the leaky bucket policer that polices
  the average rate and burst size of a packet flow.
  We now want to police the peak rate, p, as well.
  Show how the output of this leaky bucket policer
  can be fed into a second leaky bucket policer so
  that the two leaky buckets in series police the
  average rate, peak rate, and burst size. Be sure
  to give the bucket size and token generation rate
  for the second policer.

6
Token Bucket

• limit input to specified Burst Size and Average
  Rate.
• bucket can hold b tokens
• tokens generated at rate r token/sec unless
  bucket full
• over interval of length t number of packets
  admitted less than or equal to (r t b).

7
Question 2

• See figure. For the second leaky bucket, rp,
  b1.