GPS, PGPS

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GPS, PGPS WFQ

• Prof. Dr. Guido Schuster

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Leaky Bucket

• A way to describe flow i with a rate ri bits/s
  and a burst bi bits (ri,bi)
• Usually tokensbits

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GPS (General Processor Sharing)

• Each flow i has a weight fi and receives at least
  rfi / (? fk) bits/s capacity of the outgoing
  link of capacity r bits/s
• Think toothpaste ?

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Incoming/Outgoing Packets
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Leaky Bucket GPS gt Magic

• Worst case
• Burst bi arrives and all other flows k require
  service also
• Max delay per router bi / (r fi / (? fk) )

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PGPS / WFQ

• Packet-by-Packet GPS, also called WFQ
• Basic idea is to schedule packets such that the
  order of the finishing time of GPS is preserved
• Worst case (without proof)
• The biggest possible packet Lmax bits just got
  scheduled by PGPS in front of the correct packet
  (the GPS solution)
• Max Delay per Router bi / (r fi / (? fk) )
  Lmax/r
• Still magic ?

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PGPS Implementation
Source IP Telephony, Olivier Hersent, David
Gurle and Jean Pierre Petit
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PGPS Implementation
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PGPS Implementation
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PGPS Implementation
133.3
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A Network of PGPS Routers
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A Network of PGPS Routers
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RSVP Example
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RSVP Example