On the Interaction between Dynamic Routing in the Native and Overlay Layers

1
On the Interaction between Dynamic Routing in
theNative and Overlay Layers

• INFOCOM 2006
• Srinivasan Seetharaman
• Mostafa Ammar
• College of Computing
• Georgia Institute of Technology

2
Inter-Layer Interaction Problem

• Infrastructure overlay networks offer better
  services by deploying intelligent routing
  schemes.
• Uncoordinated dynamic routing in the two layers
  lead to many problems.
• We focus on the effect of native link failures,
  as they trigger each layer to reroute
  independently
• Dual Rerouting

3
Temporal Dynamics

• Consider a native link failure in CE
• Only one overlay link is affected.
• The native path AE is rerouted over F (ACE ?
  ACFDE)

G
2
3
A
I
3
2
4
E
OVERLAY
NATIVE
G
B
I
A
F
C
H

8
D
E
Cost
Overlay recovery 8
Original 2
Native Rerouting 2
Overlay rerouting 4
Time
Native Failure
Native Recovery
Native Repair
4
Downside to Dual Rerouting

• Overlap of functionality between layers causing
  large number of route flaps (oscillations)
• Unawareness of other layers decisions leading to
  
• resource overloading,
• multiple simultaneous failures
• a low success rate in rerouting
• sub-optimal paths after rerouting
• Lack of flexibility and control

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Problem Statement I

• Assume the two ends of each link (native
  overlay) use a keepAlive protocol for link
  verification.
• 3 keepAlive messages lost ? Failure
• Understand the effects of different parameters on
  the rerouting performance.
• KeepAlive-time Time between two keepAlive
  messages
• Hold-time Time window to declare link as down
• Overlay link cost scheme (Ex Native hops,
  Overlay hops)

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Performance Metrics

• Hit-time Time taken for traffic to be recovered.
  Detection time Convergence time Device
  time (depends on timers) (protocol
  specific) (Negligible)
• Success rate of recovery
• Success rate of a layer Number of paths
  recovered
• Number of failed overlay paths
• Number of route flaps
• Average route flaps Number of route flaps
• Number of failed overlay paths
• Peak Stabilized inflation (before repair)
• Path cost inflation Path cost after rerouting
• Path cost before failure

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Temporal Dynamics
Overlay path AE Overlay detects first 100
success rate 3 route flaps Peak inflation
8/2 Stabilized inflation 4/2
Hit time
8
Cost
Overlay recovery 8
Original 2
Native Rerouting 2
Overlay rerouting 4
Time
Native Failure
Native Recovery
Native Repair
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Performance Evaluation ns2

• Using GT-ITM, we randomly generate
• 25 topologies (5 overlay network) x (5 native
  network)
• Two scenarios
• Inspect intra-domain failures in single-domain
  native network
• Inspect inter-domain failures in multi-domain
  native network
• In each scenario, tabulate failure recovery
  statistics of all overlay paths by breaking one
  native link at a time

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Effect of Routing Parameters

• Observations By varying the overlay
  keepAlive-time, hold-time and cost scheme, we
  observe
• hold-time ? hit time ? (only until overlay
  hold-time lt native hold-time)
• hold-time ? route flaps ?
• hold-time ? sub-optimality ?
• keepAlive-time ? hit-time ?hold-time

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Conclusion I

• Dual rerouting can be made optimal by adopting
  the following recommendations
• Overlay hold-time very close to the native
  hold-time.
• Overlay keepAlive-time that is half that of the
  hold-time as it leads to an earlier detection.

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Problem Statement II

• Main observation from previous simulations
• Native-rerouting yields the optimal path, albeit
  a bit later
• Make the overlay layer aware of this observation
  and give higher precedence to native rerouting
  attempts
• Improve overlay routing performance by adjusting
  the overlay layer functioning

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Three Levels of Layer Awareness

• No awareness
• Dual rerouting
• Awareness of native layers existence
• Probabilistically Suppressed Overlay Rerouting
  (PSOR)
• Suppress overlay rerouting attempt with
  probability p
• Deferred Overlay Rerouting (DOR)
• Delay overlay recovery by time d

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Three Levels of Layer Awareness (contd.)

• Awareness of native layers parameters
• Follow-on Suppressed Overlay Rerouting (FSOR)
• If follow-on time lt threshold f, then suppress
  overlay rerouting

Follow-on time
Time
Overlay layer detects failure
Native layer detects failure
Failure
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Effect of Adjusting Overlay

• All three schemes are simple and offer
  significant control over the tradeoffs between
  hit-time and the other metrics.
• PSOR
• Least number of route flaps
• Least peak inflation
• DSOR and FSOR behave similarly (FSOR has slightly
  better hit-time)
• Better success rate
• Lower stabilized inflation

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Conclusion II

• By appropriately tuning
• keepAlive-time
• hold-time
• suppression probability
• delay
• follow-on threshold
• we can improve results for
• Hit-time
• Route flaps
• Path cost inflation
• Stabilization time
• Success rate

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Problem Statement III

• Main observation from previous simulations
• It is not possible to improve all metrics
  simultaneously. Hence, performance is still
  bounded!
• As overlay applications proliferate, the native
  layer should gradually evolve to suit them
• Improve overlay routing performance by adjusting
  the native layer functioning

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Tuning the Native keepAlive-time

• We adopt a non-invasive procedure to advance the
  native layer rerouting
• Tuning of the native layer keepAlive-time
• Constraints
• Tuning should not generate any extra overhead
• Effective detection time should be same

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Tuning the Native keepAlive-time (contd.)

• Consider the following scenarios for tuning.
• Scenario B is vanilla Dual rerouting
• Scenario A is the layer-aware overlay rerouting
  scheme
• Scenario C is the tuning we recommend here

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Conclusions III

• Native layer tuning we proposed achieves the best
  performance in all our metrics

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Summary

• We propose means to mitigate the problems
  associated in the inter-layer interaction
• We explore two directions
• Adjusting the overlay layer functioning
• Adjusting the native layer functioning