Congestion Control and PWE3

1
Congestion Control and PWE3

• Congestion
• Everyone sends as much as they want
• less and less traffic gets through,
• because more and more is dropped
• Congestion Control
• Feedback loop
• packet loss causes transmission rates to go down
• absence of packet loss allows rates to climb

2
Does PWE3 Need It?

• No, PWE3 mostly carries IP payloads, already
  congestion controlled
• No, PWE3 only runs in environments in which
  congestion is impossible
• Never on public Internet
• Always traffic engineered and policed
• First point worth considering, second seems
  doubtful.
• So maybe answer is yes.

3
Existing Solutions Apply?

• Existing solutions aimed at endsystem
  implementations
• PWE3 aimed at router implementation
• No acks
• No complex state machines invoked in the data
  path
• Limited interactions between
• hardware and software,
• between line cards,
• between line cards and central processor, etc.
• Rules out, e.g., use of TCP to carry PWs
• And much else

4
Detecting Congested PWs

• By sequence number gaps problematic
• Periodic marking of PW data stream
• VCCV packets with transmit counts (inserted by
  hardware just before transmission??)
• Receiving hardware inserts receive count and
  passes to processor
• Report discrepancies via control plane, perhaps
  per-tunnel
• Per-tunnel approximation??

5
Responding to Loss

• AIMD vs. TFRC vs. ??
• TFRC is slower responding, and rate based, may be
  more appropriate
• Dont want response too slow, but really dont
  want false alarms
• Why TCP friendly?
• May be on Internet
• An SP may have paying non-PWE3 customers
• Adjusting rates on TDM PWs
• Selective stopping of channels?

6
Next Steps

• Develop a detailed proposal, or
• Forget the whole thing?