Placing Relay Nodes for Intra-Domain Path Diversity

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Placing Relay Nodes forIntra-Domain Path
Diversity

• Meeyoung Cha
• Sue Moon
• Chong-Dae Park
• Aman Shaikh
• Proc. of IEEE INFOCOM 2006

Speaker ???
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Outline

• Introduction and Motivation
• Related Work
• Penalty Quantification
• Placement Algorithms
• Evaluation
• Conclusions and Comments

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Routing Instability in the Internet

• Link and router failures are frequent.
• Routing protocols are used to detect such
  failures and route around them.
• Convergence time is in the order of seconds or
  minutes.
• End-to-end connections experience long outages.
• How to increase reliability and robustness of
  mission-critical services against temporary
  end-to-end path outages?

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Path Diversity and Overlay Networks

• Take advantage of path diversity provided by the
  network topology.
• Overlay path use a node inside the network to
  relay packets over an alternate path that is
  different from the default routing path.
• ex) RON Anderson et al., SOSP 2001
• Detour Savage et al., IEEE Micro 1999
• Idea use disjoint overlay paths along with the
  default routing path to route around failures.

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Objective

• Previous work has focused on selecting good relay
  nodes assuming relay nodes are already deployed
• As an ISP, we consider the problem of placing
  relay nodes well
• Assumptions
• Intra-domain setting Shortest Path First
  Routing
• Relays are simply routers with relaying
  capability
• Overlay paths use single relay node

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Path Diversity Disjoint Overlay Path
Path Diversity Disjoint Overlay Path
ISP Network
Destination (egress router)
relays
default path
Origin (ingress router)
disjoint overlay path
Disjoint overlay path gives maximum robustness
against single link failures!
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Impact of ECMP on Overlay Path Selection

• Completely disjoint overlay paths are often not
  possible.
• - Existing path diversity Equal Cost
  Multi-Paths (ECMP)

(PoP Point of Presences, AR Access Router, BR
Backbone Router)
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Partially Disjoint Overlay Path
We may need to allow partially disjoint paths.
r
overlay path
o
d
default path
Such overlap makes networks less resilient to
failures. We introduce the notion of penalty to
quantify the quality degradation of overlay paths
when paths overlap.
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Penalty for Overlapped Links

• Impact of a single link failure on a path
• - Prob. of a packet routed from o to d
  encounters a failed link l
• P path o?d fails link l
  fails

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Penalty for Overlapped Links (cont.)

• Consider overlay path (o?r?d) is used with
  default one (o?d).
• Penalty the fraction of traffic carried on the
  overlapped link

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Penalty of relay and relay set

• Penalty of a relay r for OD pair (o,d)
• Po,d(r) P both o?r?d and o?d fail
  single link failure
• Penalty of a relay set R of size k
• sum of minimum penalty of all OD pairs using
  relays ?o,d min( Po,d(r) r ? R )

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Placement Algorithms

• How to find a relay set R of size k with minimum
  penalty
• Optimal solution
• exhaustive search, 0-1 integer programming (IP)
• Greedy selection heuristic
• start with 0 relays
• iteratively make greedy choice (minimal penalty)
• repeat until k relays are selected
• Local search heuristic
• start with k set of random relays
• repeat single-swaps if penalty is reduced

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Evaluation Overview

• Performance evaluation
• Number of relays vs. penalty reduction
• Comparison with other heuristics (random, degree)
• Sensitivity to network dynamics
• Based on topology snapshot data, do relays
  selected remain effective as topology changes?
• Based on network event logs, what is the fraction
  of traffic protected from failures by using
  relays?

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Performance Evaluation
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Relay Node Properties

• Node degree, Hop count, Path weight

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Sensitivity to Network Dynamics
5 of nodes are selected as relays
10 of nodes are selected as relays
Relays are relatively insensitive to network
dynamics.
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Hypothetical Traffic Loss from Failure Event Logs
less than 1 of traffic lost for 92.8 failures
(failure events)
complete protection for 75.3 failures
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Conclusions

• This is the first work to consider relay
  placement for path diversity in intra-domain
  routing.
• They quantify the penalty of using partially
  disjoint overlay paths and propose two
  heuristics for relay placement.
• They evaluate their methods on diverse dataset.
• Their heuristics perform consistently well
  (near-optimal).
• A small number of relay nodes (10) is good
  enough.
• Relays are relatively insensitive to network
  dynamics.

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Comments

• Evaluations are abundant.
• The comparison to Degree method is not a good
  example.

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Reference

• http//an.kaist.ac.kr/mycha/