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Congestion Control and PWE3

This article explores the challenges of congestion control in PWE3 networks and discusses potential solutions to detect and respond to congestion. It also addresses the need for congestion control in PWE3 networks and evaluates existing solutions.

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Congestion Control and PWE3

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  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 PWE3 Working Group

  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. PWE3 Working Group

  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 PWE3 Working Group

  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?? PWE3 Working Group

  5. Responding to Loss • AIMD vs. TFRC vs. ?? • TFRC is slower responding, and rate based, may be more appropriate • Don’t want response too slow, but really don’t 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? PWE3 Working Group

  6. Next Steps • Develop a detailed proposal, or • Forget the whole thing? PWE3 Working Group

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