1. New Directions and Half-Baked Ideas in Topology Modeling Ellen W. Zegura College of Computing Georgia Tech

2. Outline A very little bit of background Thoughts on: –Alternative Internet models –Scaling –Application-driven topology modeling

3. Networking background access networks hosts/endsystems routers domains/autonomous systems exchange point stub domains transit domains border routers peering lowly worm

4. Topo modeling: state-of-the-art Graph representation Router-level modeling –vertices are routers –edges are one-hop IP connectivity Domain- (AS-) level modeling –vertices are domains (ASes) –edges are peering relationships Mostly undirected and unlabeled graphs

5. Alternative Internet models 1.Intermediate AS/router level model –explicit representation for “important” routers (border routers and exchange points) 2.Hybrid real/synthetic model 3.Fluid-flow topology model –what might this mean? –alternatives to graph-based models?

6. 1: Intermediate AS/router level exchange point stub domains transit domains border routers one super-vertex per domain one vertex per exchange point and border router explicit representation of border routers endpoints of edges are border routers or exchange points

7. 2: Hybrid real/synthetic model Create database of real data for autonomous system topology Use synthetic model for high-level structure Populate synthetic model using real data stub domains transit domains transit stub

8. III: “Fluid-flow” topology model What does this mean? –alternatives to graph-based models Example: ASes occupy 2-d space; overlapping ASes can exchange traffic

9. Scaling Problem: what are the smallest topology models that capture the interesting properties? One approach: canonical topologies with a size parameter (Too) simple examples: ring, star, trees, parking lot, …

10. Possible models Domain star: One router per stub domain One transit domain One transit router per stub domain (or per k stub domains)

11. Possible models Domain single bottleneck: bottleneck between xit domains different distances between stub domains

12. What else? More transit domains Hierarchy in transit domains More multihoming (stub domain connected to more than one transit domain) Routing rules? Closer look at needs of applications

13. Application-driven models Rather than designing general models, let’s think about what particular problems need Examples: –BGP analysis –peer-to-peer (or overlay) system design

14. BGP analysis BGP – interdomain routing protocol –external BGP – between domains –internal BGP – within a domain BGP problems: –stability (do the routes oscillate?) –convergence time what are the modeling needs? –topology plus peering policies –for stability: worst case topologies –for convergence: typical topologies?

15. Peer-to-peer/overlay networks Endsystems in base network are overlay network nodes; paths in base network are overlay network links Overlay problems: –quality of overlay (length of overlay paths, load on base links,…) what are the modeling needs? –AS-level alone is sufficient? –intermediate AS/router-level is better?

16. More questions What topology models are appropriate for wireless/ad-hoc/sensor networks? What additional information is useful besides basic topology? Can a focus on the use of models lead to improved ability to evaluate the quality of models? How much do you need to know about today’s Internet to design decent models?