Multi-rate Congestion Control

1
Multi-rate Congestion Control

• Tapan Karwa
• CS590F

2
Multi-rate Data Organization

• Simulcast Different multicast groups, each
  sending all the data/signal at different rates.
• Cumulative Layered division of data. Each layer
  on a different mcast group. Higher layers refine
  data.

3
Related Work

• RLM
• Uses a state machine. Adaptive timer controlled
  experiments used to decide subscription.
• Shared learning.
• Digital Fountain Approach
• Combine Tornado codes with layered mcast, to
  enable digital fountain.
• Start drinking at any time and adapt drinking
  rate to available BW. Need any k out of (kl)

4
Related Work

• RLC Receiver-driven Layered CC
• Congestion control is achieved using SPs. Burst
  of data sent right before SP.
• Receivers make join attempts only after a SP.
  Allows new users to quickly ramp up by placing
  SPs conveniently.
• BW doubles with every higher layer and number of
  SPs decrease with every higher layer.
• Synchronizes receivers.

5
Technique

• All these schemes wait for loss before they
  react.
• Use ECN mechanism
• Dont have to wait for loss to detect congestion.
• No wastage of resources already used by packets.
• Significance for streaming video/audio.
• No loss computation at the receiver. Hence,
  faster.
• Current routers are normally in the regime of
  probabilistic marking. Effect of using ECN
  mechanisms.
• Not looked at yet!

6
Problems to be Dealt With

• How many marked packets should the receiver wait
  for One or more?
• TCP suggests considering a marked packet as a
  dropped packet and reacting accordingly. Other
  mcast CC schemes also wait for a single packet
  loss to react.
• Solutions
• Wait for a single marked packet. Too aggressive
  in dropping especially considering probabilistic
  marking.
• Wait for a subset proportional to data rate of
  highest layer. What subset? ½? Effect on TCP
  flows? Is this an engineering problem?

7
Things to be Measured

• Quality as indicated by Loss Rates
• Effect on TCP flows.
• Convergence Time
• Stability in terms of layers subscribed to.

8
Future Avenues

• Sender-based schemes using ECN information to
  dynamically alter sending rates.
• Using Diffserv mechanisms with ECN.
• Other proxy based schemes.