Media Friendly Rate Control (MFRC)

1
Media Friendly Rate Control (MFRC)

• draft-phelan-mfrc-00.txt
• Tom Phelan Sonus Networks
• tphelan_at_sonusnet.com
• 6-August-2004
• http//www.phelan-4.com/dccp/DCCP-MFRC-SanDiego.pp
  t

2
Agenda

• Background
• Thought Process
• MFRC Basics
• Next Steps

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Background

• Mailing list discussions show difficulties with
  TFRC and interactive media
• You can put the square peg in the round hole, but
  something less brutish would be nice
• Draft is a thought-experiment exploration of
  possible solution areas
• Intention is to stimulate discussion
• Could be first step on (long) path to solution

4
Thought Process

• TFRC congestion reaction pretty much OK
• Smooth rate reduction, cautious rate increase
• Biggest problems involve TFRC congestion
  avoidance mechanisms
• Slow start, restart, rate variation restrictions
• Necessary for file transfer apps

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Thought Process

• Media apps today have other congestion avoidance
  mechanisms
• Client/server pick max rate based on knowledge of
  access link speeds
• Simple, works most of the time
• Most of the time, TFRC congestion avoidance
  redundant
• So, why not let media apps guess at
  non-congesting rate, then react if the guess is
  wrong?
• Thats MFRC

6
MFRC Basics

• Three operational phases
• Uncongested phase
• Connections start here
• Free variation of transmit rate up to maximum set
  at connection start
• Yah, issues here ?
• Exit to congested phase with packet loss

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MFRC Basics

• Congested phase
• Halve allowed rate for each RTT with packet loss
• No allowed rate increases
• Exit to recovery phase after congestion
  dissipates a number of RTTs with no packet loss

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MFRC Basics

• Recovery phase
• Allowed rate variations based on TFRC
• Return to uncongested phase when TFRC allowed
  rate equals connection max rate

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Next Steps

• Mailing list discussion stimulated new ideas
• Restart bigger problem than slow start
• Byte rate better than packet rate
• Better to allow rate variations in all phases
• Simulate! Anyone willing to help?
• Wheres the home for this work?
• dccp, tsvwg, avt, something else?