Introducing the ApplicationLevel Network ALN Simulator

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Introducing the Application-Level Network (ALN)
Simulator

• By
• Nick Blundell
• n.blundell_at_comp.lancs.ac.uk
• 14 October, 2003

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Contents

• What Are Overlay/Application-Level Networks
• Motivation for the ALN Simulator
• Introduction to the ALN Simulator
• Further Work
• Summary

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Application-Level Networks (ALNs)

• An overlay network is built by peers at the
  application-level.
• Applications include
• Multicast (Application-Level).
• File storage and search.
• Drawbacks of ALNs
• Stress Packets are duplicated on network links
• Stretch Packets routed on the overlay network
  may incur extra delay over the optimal unicast
  delay in the network.

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How Are ALN Protocols Tested

• Majority of ALN research uses network simulators.
• ns-2 (free network simulator).
• OpNet (commercial).
• etc
• Straight to implementation (Gnutella).
• Testbeds Planet Lab

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Network Simulators

• Allow custom protocols to be run on nodes.
• Allow custom routing protocols to be run on
  routing nodes.
• Batch operation
• Allow visualisation of traffic on network links.
• Allow realistic Internet-like topologies to be
  used in simulations.
• Allow packet queuing and dropping in network
  routers for realistic simulations.

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ALNs and Network Simulators

• ALN protocols are loaded onto simulator nodes and
  instructed to join the overlay network or send
  data etc...
• To work out what is happening the ALN protocol
  must write events to a log file.
• Statistical data is also logged to find out how
  the protocol performed.
• Hard to see what is happening from log files and
  a only visualisation of the underlying network
  traffic.
• Usually have to wait until simulation finishes
  before finding bugs.

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ALN Visualisation

• It would be nice to have a visualisation of the
  overlay network (i.e. traffic on overlay network
  links) as well as the underlying network
  topology.
• It would also be nice to see the ALN protocol
  state in real-time (i.e. performance
  measurements, ALN node status) during the
  simulation.
• It would be nice if the simulator was interactive
  allowing instructions to be given to ALN nodes
  during the simulation (join/leave overlay, fail,
  start multicast etc) as well as the option of
  running a simulation script.
• All of these things would make it easier to test,
  debug and develop experimental ALN protocols.

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Introducing ALN Simulator

• The ALN Simulator
• Architecture
• Allows underlying network topologies to be loaded
  as with previous network simulators.
• Also allows application-level/overlay networks to
  be build upon the underlying network.
• Allows custom ALN protocols to be run on the ALN
  nodes.
• Interface
• Allows simultaneous views of both the underlying
  network and the application-level network traffic
  flow and node state.
• User can interact with the simulation in
  real-time
• Instruct an ALN node to join/Leave the overlay
  network.
• Instruct an ALN node to start transmitting data
  on the overlay.
• Fail an ALN node.
• User can also use the simulator in batch mode by
  writing a simulator script.

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Introducing ALN Simulator

• Performance Monitoring
• Debugging Protocols
• The protocol developer will quickly be able to
  see if their ALN Protocol is behaving accordingly
  by watching the overlay network being built and
  reconfigured.
• The user will also be able to see if data packets
  are being correctly routed on the overlay
  network.
• Overlay Mapping
• The overlay network and underlying network are
  presented side-by-side allowing the user to see
  how well the overlay network is mapping to the
  underlying topology.
• Stress
• Links in the underlying network view will glow
  brightly when under stress (when many duplicates
  of the same packet are present on the link)
  allowing the developer to check the protocol is
  minimising stress.
• Stretch
• ALN nodes on the overlay view have an indicator
  of the delay or stretch of incomming packets
  allowing the developer to monitor the latency
  efficiency of the ALN protocol.

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Architecture
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Introducing ALN Simulator
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Introducing ALN Simulator
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Further Work

• Simulator efficiency.
• Scripted ALN Protocols.
• Extra state information on views.
• Test my own ALN protocol

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Summary

• We looked at ALN Networks
• Existing simulators used for developing ALN
  protocols
• Motivation for an ALN Simulator
• Introduction to the ALN Simulator

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Questions?