TFRC with Self-Limiting Sources

1
TFRC with Self-Limiting Sources

• http//www.phelan-4.com/dccp/tfrc-self-limit.pdf
• Tom Phelan Sonus Networks
• tphelan_at_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
• Theres 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 dont TFRC flows look like this?

8
Its 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
• Lots 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