A FreeBSD-based prototype of a Time-Driven Priority router Mario 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 routerhost 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 as the 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 latency is 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?