A New EDF Scheduler for Providing Rate Guarantees

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A New EDF Scheduler for Providing Rate Guarantees

• Uday Mudoi
• Vitesse Semiconductors
• uday_at_vitesse.com

Raif Onvural OroBridge Inc raif_at_orobridge.com
Yannis Viniotis NC State University candice_at_ncsu.e
du
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Objective of our research

• To investigate the capability of an EDF
  scheduler to
• provide minimum rate guarantees
• distribute the unused bandwidth among the active
  users in presence or absence of traffic with
  delay guarantees

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Previous Work on EDF

• Delay EDF
• The theoretical maximum delay bound for an
  user, djmax is added to the packets arrival time
  to compute its deadline,
• Dj aj dj max
• RC-EDF
• EDF scheduler with a shaper in its front

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Proposed new EDF

• Modified EDF
• The deadline for the current packet is
  calculated at the departure of the previous
  packet from the same connection. The deadline Dj
  i for a packet i from FLOWj is calculated as
• Dj i max(aj, depj i-1 dj max).
• where, aj denotes the arrival time of packet i
  from FLOWj and depj i-1 denotes the departure
  time of packet i-1 from FLOWj

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Simulation Environment

• Single switch with multiple source and multiple
  destination ports
• Sources
• Constant rate
• bursty three state source model with active
  periods (A), idle periods (I), pause periods (P),
  the number of packets per active period (M), and
  the size of packets (S)
• Per flow queuing
• Infinite buffering

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Simulation Results

• Deadline calculation at arrival

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Simulation Results

• Deadline calculation at departure

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Deadline at Arrival

• Let us take four connections each with a PR of 1
  packet per second. Let us assume that,
• connection 1 has a MR of 1 packet per 2 seconds,
• connection 2 has a MR of 1 packet per 3 seconds
• connection 3 has a MR of 1 packet per 4 seconds
• connection 4 has a MR of 1 packet per 5 seconds
• So the departure time for packets starting at
  t1,
• for connection 1 3, 4, 5, 6, 7, 8, 9, 10
• for connection 2 4, 5, 6, 7, 8, 9, 10, 11...
• for connection 3 5, 6, 7, 8, 9, 10, 11...
• for connection 4 6, 7, 8, 9, 10, 11...

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Simulation Results

• Resultant bandwidth transients with EDF
  scheduling, deadline calculation at arrival

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Simulation Results

• Resultant bandwidth with bursty sources with EDF
  scheduling, deadline calculation at arrival

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Deadline at Departure

• Let us take four connections each with a PR of 1
  packet per second. Let us assume that,
• connection 1 has a MR of 1 packet per 2 seconds,
• connection 2 has a MR of 1 packet per 3 seconds
• connection 3 has a MR of 1 packet per 4 seconds
• connection 4 has a MR of 1 packet per 5 seconds
• So the departure time for packets starting at
  t1,
• for connection 1 3, 5, 7, 9, 11...
• for connection 2 4, 7, 11, 14...
• for connection 3 5, 9, 13, 17...
• for connection 4 6, 11, 16, 21...

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Simulation Results

• In presence of both Delay and Rate traffic,
• deadline calculation at arrival

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Conclusions

• EDF scheduling with deadline calculation at
  departure can provide isolation among sources
  requiring rate guarantees traditional
  implementations of EDF scheduling, with deadline
  calculation at arrival cannot provide this
  feature.
• The bandwidth share in EDF scheduling with
  deadline calculation at departure is proportional
  to the minimum rate allocated to the connections
  when calculation is done at arrival, the
  bandwidth share follows the arrival pattern of
  the connections