Max Allocation with Reservation (MAR) BW Constraint Model for MPLS/DiffServ TE

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Max Allocation with Reservation (MAR)BW
Constraint Model for MPLS/DiffServ TE
Performance Comparisons(draft-ash-mpls-dste-bcmod
el-max-alloc-resv-01.txt)
Jerry Ash gash_at_att.com

• Outline
• brief review
• you have read the draft
• concepts dynamic bandwidth reservation MAR
• analysis of MAR
• issues
• conclusions

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MAR Bandwidth Constraint Model

• allocates bandwidth to individual class types
  (CTs)
• like the Maximum Allocation Model (MAM)
• protects allocated bandwidth by bandwidth
  reservation methods, as needed, but otherwise
  fully share bandwidth
• meets all requirements for BC models
• works well with or without preemption
• supports greater efficiency in bandwidth sharing
• provides protection of allocated bandwidth under
  congestion
• allows bandwidth sharing in absence of congestion
• based on mechanisms in use for 10 years for
  multiservice voice/data bandwidth allocation in
  large-scale networks

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Dynamic Bandwidth Reservation

• gives preference to certain traffic
• for class types (CT) below their BWalloc
• on preferred (shortest) path
• preferred traffic allowed to seize any idle
  bandwidth on a link
• non-preferred traffic (on CT above BWalloc or on
  alternate paths) can seize bandwidth only if
  there is a minimum level of idle bandwidth
  (called the bandwidth-reservation threshold)
• on congested link preferred traffic sees low loss
  while non-preferred traffic sees much higher loss
• this situation maintained across wide variation
  in percentage of preferred traffic
• bandwidth reservation robust to traffic
  variations
• as shown in mathematical models in simulation
  studies
• very widely used in practice

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Illustrative Use of MARLink Load States
Allowed Load State

• local link states kept of idle link bandwidth
• reserved-bandwidth (RBW)
• less than RBW requested BW available
• available-bandwidth (ABW)
• more than RBW requested BW available
• bandwidth-not-available (BNA)
• not enough bandwidth for flow/LSP
• allowed load states for flow/LSP setup
• when BW lt BWalloc any idle link bandwidth can be
  seized if link not in BNA state
• both RBW ABW states allowed
• when BW gt BWalloc, links must be in ABW state
• RBW state not allowed

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Illustrative Use of MAR
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Analysis of MAR

• options compared
• MAR -- flows/LSPs set up with bandwidth
  reservation
• full sharing -- flows/LSPs set up without
  bandwidth reservation
• full-scale 135-switch national network simulation
  model
• 5 CTs -- normal priority voice, high priority
  voice, normal priority data, high priority data,
  best-effort data

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Performance Comparison forMAR Full Sharing
Bandwidth Constraint Models6X Focused Overload
on Oakbrook(Total Network Lost/Delayed Traffic)
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Performance Comparison forMAR Full Sharing
Bandwidth Constraint Models50 General
Overload(Total Network Lost/Delayed Traffic)
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Issues

• all BC models MUST meet all requirements
• e.g., MUST NOT require use of preemption to work
  well
• many comments on list in support of this
• more important now since all BC models are
  optional
• SPs dont want to get stuck with BC model not
  meeting requirements
• comparisons of BC models
• Russian Doll Model (RDM)
• can work poorly when preemption not enabled
• too much sharing under overload can degrade
  performance of some CTs
• needs to be modified to have acceptable
  performance when preemption not enabled
• MAM MAR
• provide protection of allocated bandwidth under
  congestion
• MAR allows BW sharing in absence of congestion

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Issues

• protection from pathological traffic patterns
  use
• issue for all BC models
• protect against any possible scenario, however
  unlikely or atypical?
• examples given of bandwidth hogging
• could add upper limits on allocated bandwidth to
  mitigate
• but is this necessary?
• DS-TE is a bandwidth allocation procedure,
  involving use of CAC
• CAC bandwidth allocations related to traffic
  demands
• experience doesnt match bandwidth hogging
  scenarios
• need common assumptions of traffic
  characteristics engineering use
• assume DS-TE use based on common assumptions

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Conclusions

• MAR bandwidth constraint model
• protects allocated bandwidth by bandwidth
  reservation methods, as needed, but otherwise
  fully share bandwidth
• meets all requirements for BC models
• works well with or without preemption
• supports greater efficiency in bandwidth sharing
• provides protection of allocated bandwidth under
  congestion
• allows bandwidth sharing in absence of congestion
• need common assumptions of traffic
  characteristics engineering use
• proposed next steps in specifying BC models
• specify/progress MAM
• specify/progress MAR
• hold off on specifying/progressing RDM
• needs modification to not perform poorly when
  preemption not enabled

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Backup Slides
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Dynamic Bandwidth Reservation Performanceunder
10 Overload
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Network Instability Under Congestion

• under congestion networks can exhibit
  instability with drastic loss of network
  throughput
• by as much as 50 of traffic carrying capacity
• shown mathematically in NaM73, Kru82, Aki84
  in numerous simulation studies
• simple example fully-connected network with
  first-choice routing on the 1-link direct path
  or, if unavailable, on (one of many) 2-link
  alternate paths
• under congestion 1-link direct path often not
  available 2-link alternate path may be found
  and used
• 2-link connections take twice the resources as
  1-link connections, which leads to more
  congestion and more alternate routing on 2-link
  connections
• can lead to two possible network states
• most or all connections on 1-link paths (desired
  condition)
• most or all connections on 2-link paths (half the
  throughput)
• solution use dynamic bandwidth reservation to
  favor shortest paths vs. longer alternate paths