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Scalability and Accuracy in a Large-Scale Network Emulator. Nov. 12, 2003 Byung-Gon Chun. Contents. Introduction Architecture Implementation and Evaluation Accuracy vs. Scalability Tradeoff Case Studies. Motivation. Real-world experiments

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Presentation Transcript
contents
Contents
  • Introduction
  • Architecture
  • Implementation and Evaluation
  • Accuracy vs. Scalability Tradeoff
  • Case Studies
motivation
Motivation
  • Real-world experiments
    • It is hard to deploy and administer research software at distributed sites
    • Results are not reproducible
  • Simulation
    • It misses important real system interactions
    • Tools do not support direct execution of software
  • Emulation
    • Unmodified applications
    • Almost reproducible results
    • Important system interactions
contribution
Contribution
  • Large-scale network emulator that can emulate network dynamics in a topology
  • Techniques to trade increased scalability for reduced accuracy
  • Evaluation of a range of systems
architecture
Architecture

EN

VN

CR

Pipe

modelnet phases
ModelNet Phases
  • Generate a network topology
  • Source: Internet traces, BGP dumps, Synthetic topology
  • Target: GML
modelnet phases1
ModelNet Phases
  • Source: GML
  • Target: Pipe topology
  • Optionally, simplify the network
modelnet phases2
ModelNet Phases
  • Map components of the distilled topology to core nodes
  • Minimize the bandwidth demands
  • Greedy algorithm
modelnet phases3
ModelNet Phases
  • Assign VNs to ENs
  • Multiplex VNs
  • Bind an EN to a CR
  • Generate configuration scripts
  • Install pipes and routing tables to CRs
  • Set up IP addr for VNs
core router
Core Router
  • Routing table
    • Memory vs Computation Tradeoff
  • Descriptors referencing buffered packets
  • Schedule descriptors on pipes using a heap
  • Admission control of packets injected
  • Multihop and multi-core
discussion
Discussion
  • Resource isolation
    • UDP flows
  • Routing protocol
    • Assumes shortest path routing and instantaneous repair of node and link failures
    • Routing protocol dynamics (update propagation)
  • Flexibility to inject routing algorithms
    • Policy-based routing
evaluation of implementation
Evaluation of Implementation
  • Accuracy - 1ms worst-case error per hop
  • Capacity
    • 120000 packets/s with 1 hop
    • 90000 packets/s with 8 hops
  • Core crossing
    • For 4 node configuration and 2 hop paths,

0% cross-core traffic – 462.5Kpkt/s

100% cross-core traffic – 155.8Kpkt/s

    • Depends on target topology and application communication patterns
accuracy vs scalability tradeoffs
Accuracy vs. Scalability Tradeoffs
  • Continuum balancing accuracy and cost
  • Distillation
    • Reduce the diameter of the network
    • Hop-by-hop
    • End-to-end: bottleneck bandwidth, latency, loss rate
    • Walk-in and walk-out(?)
    • Other approaches?
    • Tradeoffs?
  • Flow-based [Narses]
  • – No wall-clock time or network size?
accuracy vs scalability tradeoffs2
Accuracy vs. Scalability Tradeoffs
  • VN multiplexing
    • Howto? Mapping of multiple VNs to a EN
    • Context switch, scheduling and resource contention
    • Concurrency model
    • Number of processes  Aggregate thp. 
  • Network characteristics
    • Howto? Synthetic background cross traffic in CRs
    • Do not capture all packet dynamics (TCP slow start, bursty traffic)
    • Network change - recompute shortest paths
      • Fault injection like partitions, bandwidth change
case studies
Case Studies
  • 10000 node gnutella network emulation
  • CFS, Replicated web services, Adaptive overlays, Ad hoc networking(?)
  • CFS: reproduce the published experimental results
  • Replicated web services: support for realistic Internet topologies and emulation of contention of shared pipes
  • Adaptive overlays: subject systems to dynamically changing network conditions
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