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Link-Level Internet Structures

Link-Level Internet Structures. Scott Schremmer and Kevin Wampler. Overview. Structure of Internet not by chance Economic factors influence structure Two areas of focus: Single ISP structure Multiple ISP structure. Single ISP Simulation. Focus on network topology Internet is a graph

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Link-Level Internet Structures

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  1. Link-Level Internet Structures Scott Schremmer and Kevin Wampler

  2. Overview • Structure of Internet not by chance • Economic factors influence structure • Two areas of focus: • Single ISP structure • Multiple ISP structure

  3. Single ISP Simulation • Focus on network topology • Internet is a graph • Nodes: points of presence • Population served • Geographic location • Edges: physical links • Bandwidth capacity • Need some economic information

  4. Link Cost • Function of distance and capacity • Two components • Cost of cable • Cost of laying cable

  5. Bandwidth Cost • Cost is per unit length cable • Linear in distance • Multiple cables linear in bandwidth • So single cable sublinear in bandwidth • We choose

  6. Traffic Routing • Assume shortest-hop • Distributed evenly amongst population • Traffic between n1 and n2:

  7. Calculating Load • Sum of traffic across link • For each node: • Compute shortest-hop routes • For each target node: • Add traffic to load on all links on route • If load exceeds capacity, excess is overload

  8. Generating Networks • Incremental Growth • Likely a reasonable model • Mimics and ISP adding new POPs • Growth of ISP matters • Global optimization • Entire network planned in advance

  9. Incremental Growth Model • Investigated by Barabasi and Albert • Link probability proportional to degree • Yields power degree distribution • Applicability is unclear • Suboptimal links chosen too often • No direct economic incentive

  10. A Better Model • New nodes added randomly • Optimal link always chosen • Provisioned so no overload • Topology depends on “optimal” • Cost of new link • Cost of new and replaced links • Overprovisioning

  11. Cost Of New Link • Light tailed

  12. Replaced Links • Very heavy tailed

  13. Overprovisioning • Close to power distribution

  14. Global Optimization • Optimize entire network • Growth does not matter • Need objective function • Minimize cost while providing good service • Depends on weighting

  15. Generating A Network • Initially Random • Use Simulated Annealing • Add a link • Remove a link • Grow a link • Shrink a link

  16. Cost/Service Emphasis cost service

  17. Degree Distributions

  18. Single ISP Conclusions • Topologies similar to reality from: • Minimizing load/link replacement with overprovisioning • Overconnection to improve service

  19. Extension to Multiple ISP’s • Consider that ISPs do not grow in a vacuum • How does model change with introduction of more ISP’s • Link level structures • Economic Choices • Router distributions and routing choices

  20. Specifics of simulation • Simulated annealing • 2 ISP annealed separately • Some number of iterations with one • Pass shared parameters (inter-isp traffic) • Recalculate parameters for annealing separately • Routing-2 models • Small ISP lets large ISP route to cities it doesn’t cover • Small ISP routes to its border

  21. 2 Internets. . .

  22. Future work • Consider evolving model • If an isp is providing better service or has lower cost increase its market share • Structures that result • Conditions for isp to survive • Stable? • Anneal together cooperatively, how different are structures • Add nodes to small network to simulate growth

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