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 Nodes: points of presence Population served Geographic location Edges: physical links Bandwidth capacity Need some economic information

Link Cost Function of distance and capacity Two components Cost of cable Cost of laying cable

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

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

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

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

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

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

Cost Of New Link Light tailed

Replaced Links Very heavy tailed

Overprovisioning Close to power distribution

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

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

Cost/Service Emphasis

Degree Distributions

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

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

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

2 Internets. . .

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