New Directions and Half-Baked Ideas in Topology Modeling Ellen
W. Zegura College of Computing Georgia Tech
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Outline A very little bit of background Thoughts on:
Alternative Internet models Scaling Application-driven topology
modeling
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Networking background access networks hosts/endsystems routers
domains/autonomous systems exchange point stub domains transit
domains border routers peering lowly worm
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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
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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?
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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
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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
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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
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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,
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Possible models Domain star: One router per stub domain One
transit domain One transit router per stub domain (or per k stub
domains)
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Possible models Domain single bottleneck: bottleneck between
xit domains different distances between stub domains
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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
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Application-driven models Rather than designing general models,
lets think about what particular problems need Examples: BGP
analysis peer-to-peer (or overlay) system design
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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?
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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?
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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 todays Internet to design decent
models?
