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

1. Politecnico di Torino Istituto Superiore Mario Boella A FreeBSD-based prototype of a Time-Driven Priority router Mario Baldi Guido Marchetto

2. 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

3. Network prototype topology TDP network router host

4. Router architecture • PC based • FreeBSD operating system • Four components: • TDP input classifier • TDP output buffers (ALTQ extension) • TDP scheduler • Asynchronous input shaper(Dummynet extension)

5. 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

6. Implementation issues • Interfaces are not served at the same time • Interrupts are served with latency • Both servicing times are variable

7. 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

8. 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

9. 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

10. Thank you. Questions?