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Understanding TFRC with Self-Limiting Sources in Network Simulations

Explore the impact of self-limiting sources on TFRC in network simulations, focusing on fair throughput allocation and VoIP implications. Update includes TFRC fairness in packet rate and adjustments for VoIP mode. Feedback welcome.

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Understanding TFRC with Self-Limiting Sources in Network Simulations

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  1. TFRC with Self-Limiting Sources http://www.phelan-4.com/dccp/tfrc-self-limit.pdf Tom Phelan – Sonus Networks tphelan@sonusnet.com 9-November-2004 http://www.phelan-4.com/dccp/DCCP-TFRC-self-limit-DC.ppt

  2. Motivation • File transfer type applications are greedy • They will attempt to consume all available bandwidth • Streaming media is not • There’s some maximum throughput that will satisfy the app • TFRC simulations to date have used simulated file transfer type applications • What happens when self-limiting sources using TFRC compete with TCP file transfer sources?

  3. The VoIP Media Source • Simulates G.711 VoIP • One 8-bit sample every 125 µs • Samples periodically assembled into packets • 10 ms gives 80 bytes of voice payload • Add RTP header (12 bytes), UDP header (8 bytes) and IP header (20 bytes) • Makes 100, 120-byte packets per second – 96K bps

  4. Simulated Network • Three major scenarios: • Cable access, inbound (1.5M bps chokepoint) • Cable access, outbound (256K bps chokepoint) • Server farm (45M bps chokepoint)

  5. Simulation 1 • 1.5M bps chokepoint • 1 TCP, 1 TFRC • Reasonable performance

  6. Simulation 3 • 6 TCP, 1 TCP • Fair share is about 214K bps • TFRC driven down to about 20K bps • Hello? Hello?

  7. Simulation 7 • Use pure CBR without TFRC • Flow loses packets, but gets OK throughput • Why don’t TFRC flows look like this?

  8. It’s Packet Rate, not Byte Rate (stupid) • Dado Colussi pointed out – TFRC goal is fairness in packet rate, not byte rate • Measured in pps, TFRC source is getting fair share (even a little more) • Little comfort to the people trying to have a conversation, though  • Paper updated for this in late October

  9. VoIP Mode (or Sally to the rescue) • Special dispensation for apps that send no more than 100 pps • Throughput computation adjusted to be fair in bps to TCP with big packets • More from Sally after this • Lot’s of work to do, but looks promising

  10. VoIP Mode Simulation

  11. DCCP User Guide • Was looking grim before VoIP mode • Needed to reconsider almost entire content • But if VoIP mode stands up, so does current content • Some tweaks needed • Need feedback • Held off asking because so much feedback happening on main spec and CCIDs

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