A FreeBSD-based prototype of a Time-Driven Priority

routerMario Baldi

Guido Marchetto

Politecnico di Torino

Istituto Superiore Mario Boella

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

router hostrouter host

TDP network

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?