1. Performance Guarantees

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1. Performance Guarantees

• Introduction
• by asking sources about flow behavior it is
  possible to construct networks that could
  guarantee performance for individual flows
• traffic management involves queue management

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2. Statistical vs Deterministic

• Deterministic guarantees all data will arrive
  within a delay D
• Statistical guarantees some percentage of data
  (very large) will arrive within the delay D

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2.1 What is guaranteed ?

• worst case loss rate , bandwidth , queueing
  delay
• Effective loss rate arrive to late or queue
  overflow
• Size of queue is important - size and delay
  are related - if too small overflow

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3.Statistical multiplexing

• term for taking traffic from a number of
  sources and forwarding it out the same output
  line
• rely on law of large numbers
• the bandwidth is constant but does not state what
  the required aggregate bandwidth will be

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• is unguaranteed traffic purely random?
• for telephone networks is random
• data traffic is correlated even from a very
  large number of sources
• data network traffic is self-similar or fractal

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3.1 Makruckis Proposal

• scheme for management of guaranteed flows in ATM
  networks
• if a source exceed its rate turn on CLP
• cells with CLP on may be dropped
• simple

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3.2 Performance Bounds

• packet train effects becomes stronger as a flow
  path gets longer
• TCP acknowledgements can get compressed
• cells from the same connection are moved closer

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3.3 How to deal with worst case?

• Constrain the sources , so that it is harder to
  form bunches
• Remix the traffic periodically
• Statistical guarantees expressed in term of
  connections with infinite lifetimes
• Used in backbones

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4. Weighted fair Queuing

• Maintain a queue for each source and forward the
  packets in round-robin order - ignores packet
  length - sensitive to the patterns of packet
  arrivals
• bit by bit round robin
• weighted fair queuing

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4.1 Performance

• Expensive to implement
• - maps each packet to its flow
• - maintain a queue

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5. Jitter Control Schemes

• In weighted fair queueing packet will arrive no
  later than tD
• tx
• x can vary by a value called jitter

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5.1 Stop and Go Queuing

• Input frames

Output frames
All frames have T bits
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• Delay D p ? d
• p - propagation delay
• ? - fixed delay
• d - small variance
• h T lt ? lt 2hT , h - path length
• -T lt d lt T
• Delay is bounded by p?d

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5.2 Jitter EDD

• Jitter Earliest Due Date
• When flow is established - each hop is
  given a queuing budget b - each hop has a jitter
  bound j
• When packet is transmitted records the difference
  s t-b
• At next hop s is added to b

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6. Statistical multiplexing revisited

• Weighted fair queueing , Stop and Go , jitter EDD
  guarantees are very long
• FIFO incorporate low delays of statistical
  multiplexing with delay guarantees

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6.1 FIFO

• Limit delay accumulation
• - Hops groups flows into classes
• - Difference between the queueing delay
  and average queueing delay of class