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Politecnico di Torino Istituto Superiore Mario Boella. A FreeBSD-based prototype of a Time-Driven Priority router. Mario Baldi Guido Marchetto. Goals. First implementation of TDP Until now analytical studies and software simulations only Identification of possible criticalities

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Politecnico di Torino

Istituto Superiore Mario Boella

A FreeBSD-based prototype of a Time-Driven Priority router

Mario Baldi

Guido Marchetto


Goals

  • First implementation of TDP

    • Until now analytical studies and software simulations only

    • Identification of possible criticalities

  • Visually show TDP benefits through multimedia demonstration

    • Video quality with TDP vs asynchronous packet switching


Network prototype topology

TDP network

router

host


Router architecture

  • PC based

  • FreeBSD operating system

  • Four components:

    • TDP input classifier

    • TDP output buffers (ALTQ extension)

    • TDP scheduler

    • Asynchronous input shaper(Dummynet extension)


Common Time Reference (CTR)

  • Adopted card: Symmetricom

    • Periodic interrupt over the PCI bus

    • Programmable interrupt frequency

  • Each interrupt represents the beginning

  • of a new TF


Implementation issues

  • Interfaces are not served at the same time

  • Interrupts are served with latency

  • Both servicing times are variable


Consequences

  • Transmissions do not start as soon asthe TF begins

    • Violation of nominal time frame boundaries

  • Transmissions start with a variable delay

  • Potential bandwidth waste


Facts

  • Latency equivalent to longer links

    • Interrupt and interface service latencyis low

  • Latency variation is absorbed by “delaying” forwarding time-frame

    • Interrupt and interface service latency has low variability

  • “EXTRA” CROSSING DELAY IN THE NODE

  • “EXTRA” BUFFERING IN ORDER TO HANDLE THIS DELAY


Conclusions

  • Contribution

    • Proof of concept:

      • Algorithm and system semplicity(~1000 LOC)

      • PC architecture can support TDP

  • Future work

    • Performance evaluation

    • Realization of the network testbed and demonstration


Thank you.

Questions?


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