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On Selfish Routing In Internet-like Environments. Lili Qiu (Microsoft Research) Yang Richard Yang (Yale University) Yin Zhang (AT&T Labs – Research) Scott Shenker (ICSI). ACM SIGCOMM 2003. Selfish Routing. IP routing is often sub-optimal in terms of user performance Many causes

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on selfish routing in internet like environments

On Selfish Routing In Internet-like Environments

Lili Qiu (Microsoft Research)

Yang Richard Yang (Yale University)

Yin Zhang (AT&T Labs – Research)

Scott Shenker (ICSI)


selfish routing
Selfish Routing
  • IP routing is often sub-optimal in terms of user performance
    • Many causes
      • Routing hierarchy, policy routing, failures, instability
  • Emerging trend: Autonomous routing
    • End users choose their own routes
      • Source routing (e.g. Nimrod)
      • Overlay routing (e.g. Detour, RON)
  • Autonomous routing is selfish by nature
    • End hosts or routing overlays greedily select routes to optimize their own performance without considering system-wide criteria


bad news

L1(y) = 1



L0(x) = xn

Total load: x + y = 1

Average latency: x L0(x) + y L1(y)

Bad News
  • Roughgarden and Tardos showed that selfish routing can result in serious performance degradation with general latency functions and topologies
  • The worst-case price-of-anarchy is unbounded
    • Selfish source routing
      • At equilibrium all traffic goes through the lower link
      •  Average latency = 1
    • Latency optimal routing
      • To minimize average latency, set x = [1/(n+1)] 1/n
      •  Average latency  0 as n  


  • Selfish source routing
    • How does selfish source routing perform?
      • Are Internet-like environments among the worst cases?
  • Selfish overlay routing
    • How does selfish overlay routing perform?
      • Note that routing on an overlay has much less flexibility than routing directly on the physical network.
  • Horizontal interactions
    • Does selfish traffic co-exist well with the remaining traffic that uses default IP routing (e.g., OSPF)?
    • Do selfish overlays co-exist well with each other?
  • Vertical interactions
    • How does selfish traffic interact with the underlying network control process, i.e. traffic engineering?


our approach
Our Approach
  • We take a game-theoretic approach to partially answer these questions through simulations
    • Focus on equilibrium behavior
      • Apply game theory to directly compute traffic equilibria
      • Compare the performance of traffic equilibria with global optima and default IP routing
    • Focus on intra-domain environments
      • Compare against theoretical worst-case results
      • Can use realistic topologies, traffic demands, and latency functions
  • Disclaimers
    • Lots of simplifications & assumptions in the paper
      • Necessary to limit the parameter space
    • Raise more questions than what we answer
      • Lots of ongoing and future work


routing schemes
Routing Schemes
  • Routing on the physical network
    • Source routing
    • Latency optimal routing
  • Routing on an overlay (less flexible!)
    • Overlay source routing
    • Overlay latency optimal routing
      • Cooperative within an overlay, but selfish across overlays
  • Compliant (i.e. default) routing: OSPF
    • Hop count, i.e. unit weight
    • Optimized weights
      • Minimize network cost [FRT02]
    • Random weights


internet like environments
Internet-like Environments
  • Network topologies
    • Real topology from an operational tier-1 ISP
    • Rocketfuel topologies
    • Random power-law topologies
  • Logical overlay topology
    • Fully connected mesh (i.e. clique)
  • Traffic demands
    • Real traffic demands from the tier-1 ISP
    • Synthetic traffic demands
  • Link latency functions
    • Queuing delay: M/M/1, M/D/1, P/M/1, P/D/1, BPR
      • Avoid discontinuity by using a linear tail at utilization > 99%
    • Propagation delay: fiber length or geographical distance divided by the speed of light
  • Performance metrics
    • User: Average latency
    • System: Maximum link utilization, network cost [FRT02]


selfish source routing average latency
Selfish Source Routing: Average Latency

Good news: Internet-like environments are far from the worst cases for selfish source routing


selfish source routing network cost
Selfish Source Routing: Network Cost

Bad news: Low latency comes at much higher network cost


selfish overlay routing
Selfish Overlay Routing
  • Similar results apply
    • Selfish overlay routing achieves close to optimal average latency
    • Low latency comes at higher network cost
  • The results apply when the overlay only covers a fraction of nodes
    • Scenarios tested:
      • Random coverage: 20-100% nodes
      • Edge coverage: edge nodes only


horizontal interactions
Horizontal Interactions

Different routing schemes coexist well without hurting each other. With bad weights, selfish overlay also improves compliant traffic.


vertical interactions
Vertical Interactions
  • Vertical interaction: An iterative process between two players
    • Traffic engineering: minimize network cost
      • current traffic pattern  new routing matrix
    • Selfish overlays: minimize user latency
      • current routing matrix  new traffic pattern
  • Question:
    • Will the system reach a state with both low latency and low network cost?
  • Short Answer:
    • It depends on how much underlay routing has


selfish overlays vs ospf optimizer
Selfish Overlays vs. OSPF Optimizer

OSPF optimizer interacts poorly with selfish overlays because it only has very coarse-grained control.


selfish overlays vs mpls optimizer
Selfish Overlays vs. MPLS Optimizer

MPLS optimizer interacts with

selfish overlays much more effectively.


  • Formulate a set of important research questions on selfish routing
  • Use game theory and simulations to partially answer them in the intra-domain context
  • A number of interesting findings
    • In contrast to the theoretical worst cases, selfish routing achieves close to optimal latency in Internet-like environments.
    • Selfish overlays co-exist well both with each other and with traffic using default IP routing
    • Mismatch between objectives of selfish overlays and traffic engineering has significant impact on system performance


lots of future work
Lots of Future Work
  • Answer the questions in inter-domain context
  • Study dynamics of selfish routing (i.e., how are traffic equilibria reached?)
  • Study alternative selfish routing objectives (e.g., loss and throughput)
  • Study the effects of different logical overlay topologies
  • Improve the interactions between selfish routing and traffic engineering



Thank you!


computing traffic equilibrium of selfish routing
Computing Traffic Equilibrium of Selfish Routing
  • Computing traffic equilibrium of non-overlay traffic
    • Use the linear approximation algorithm
      • A variant of the Frank-Wolfe algorithm, which is a gradient-based line search algorithm
  • Computing traffic equilibrium of selfish overlay routing
    • Construct a logical overlay network
    • Use Jacob's relaxation algorithm on top of Sheffi's diagonalization method for asymmetric logical networks
    • Use modified linear approximation algo. in symmetric case
  • Computing traffic equilibrium of multiple overlays
    • Use a relaxation framework
      • In each round, each overlay computes its best response by fixing the other overlays’ traffic; then the best response and the previous state are merged using decreasing relaxation factors.