Asymmetric Best Effort ABE

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Asymmetric Best Effort (ABE)

• Paul Hurley and Jean-Yves Le Boudec
• ICA, EPFL

CH-1015 Ecublens leboudec_at_epfl.ch http//icawww.ep
fl.ch
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Contents

• 1. Requirements for Interactive Multimedia
• 2.Asymmetric Best Effort service definition
• 3. Implementation
• 4. Outlook

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1. Requirements for Interactive Multimedia

• Internet Telephony or HiFi Audio,
  Videoconferencing
• Two requirements
• low delay jitter maybe lt 50 ms
• minimum throughput 2.5 kb/s or more

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Providing a Minimum Throughput

• Three possible approaches
• hard guarantee reservations (Arequipa, RSVP
  with controlled load)
• soft guarantee priority (premium or assured
  service)
• no guarantee best effort with adaptive
  applications
• All three approaches have a market
• reservation special services (Intranet backbone,
  Telepoly)
• priority intranet voice or SNA traffic
  internet 1st class traffic
• best effort mass market
• This paper concentrates on best effort services

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Delay Jitter

• Worst case delay in msec for packets of size 1500
  Bytes
• Budget of 10 msec per node requires small buffers
  at bit rates up to 150 Mb/s

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Standard Approaches for Low Delay Jitter

• Delay Priorities of NBBS, ATM or Frame
  RelayPremium Service
• might violate sequence when combined with
  standard service
• They do not fit for best effort traffic
• require traffic management or billing to prevent
  every packet to be marked low priority

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Providing Low Delay Jitter

• with reservation services
• negotiate a low jitter reservation
• with priorities
• premium service
• with best effort service
• impossible today

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2. The Asymmetric Best Effort Service Definition
(1)

• Goal
• provide a low jitter service
• for best effort
• assumes applications are TCP-friendly
• which requires no special billing

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The Asymmetric Best Effort Service Definition (2)

• Best effort packets are marked either Green or
  Blue
• Green packets receive lower delay jitter, but
  also less throughput on saturated paths than Blue
  packets
• For a given path, the throughput for Green is b
  times less the throughput for Blue
• example with b 3 on next slide

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Blue Flow
Without ABE
Green Flow
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Green Flow
Without ABE
4 ms
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In the Internet, throughput is controlled by Loss

• Today, TCP or TCP friendly applications adjust
  their rates in reaction to losses
• using additive increase, multiplicative
  decrease
• provides a fairness close to proportional fairness

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Throughput Differential

• For an observed loss ratio q , long term
  throughput is roughly proportional to
• Thus, Green packets should experience a drop
  ratio a times higher that Blue packets, with a of
  the order of b2

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Choosing Green or Blue

• Application decides whether a packet is Green or
  Blue
• Application with file transfer semantics
• low jitter is not a value, therefore choose
  blue
• Application with interactive multimedia
  semantics
• low jitter is a value as long as a minimum rate
  is achieved

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Load (Nb of blue sources on bottleneck)
Throughput for one source (Log)
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Global Aspects

• If all traffic is Blue
• same as standard best effort
• If all traffic is Green
• equivalent to standard best effort with smaller
  buffers, hence lower overall throughput (but
  lower delay jitter)
• Blue is neither better nor worse than Green

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Overall Benefits to All

• If a source sends some green packets, it is
  because it sees sufficient value in low delay
  jitter
• If a blue source becomes green, throughput of all
  other sources increases
• blue sources get at least as much as in todays
  colorless Internet
• Compared to colorless best effort, there is
  benefit to all
• This justifies offering ABE at the same charge

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3. Implementation

• No major changes in Internet hosts or routers
• Hosts
• application logic to mark packets as green or
  blue
• by default, packets are blue
• Routers
• differential drop ratio
• low delay to green
• No special charging system

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Router Support
Time 7
Scheduler

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7





Packet Admission Control (PAC)
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2
1
0
Dropped Packets


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Router Aspects

• A single queue for Green and Blue packets
• Packet Admission Control (PAC)
• decides whether an incoming packet is accepted or
  not
• based on a variant of RED
• drop probability qB is computed based on a
  smoothed estimator of total buffer length
• for a blue packet drop probability is qB
• for a green packet drop probability is a qB

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• a is updated in order to drive the effective drop
  ratio am towards the target value at

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Packet Scheduling And Maximum Delays

• Earliest Deadline First scheduler
• packets sorted by deadline
• deadline is allocated when a packet is accepted
  in buffer
• blue packet deadline now D
• green packet deadline now
• D is a fixed parameter (ex D 100 ms)
• Worst case waiting time for blue packets is
  Ltot/C D
• Worst case waiting time for green packets is L0/C

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Side Effect of Delay on Throughput

• TCP congestion control introduces an (undesired)
  bias against high delay connections
• This must be compensated by increasing a when the
  queuing delay for blue packets increases

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4. Outlook

• The Asymmetric Best Effort service provides a new
  dimension in a best effort network
• low jitter service
• no traffic management or billing complexity
• a best effort service
• Our research focuses on
• finalizing router implementation
• Find the right values for service definition