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 Global optimization
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

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