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15. Suggested SCTP Protocol Parameter Values

This chapter summarizes recommended values for key SCTP protocol parameters.

15.1. RTO Parameters​

  • RTO.Initial: 3 seconds (3000 ms)
  • RTO.Min: 1 second (1000 ms)
  • RTO.Max: 60 seconds (60000 ms)
  • RTO.Alpha: 1/8 (0.125) - SRTT smoothing factor
  • RTO.Beta: 1/4 (0.25) - RTTVAR smoothing factor

15.2. Maximum Retransmission Limits​

  • Association.Max.Retrans: 10 attempts
  • Path.Max.Retrans: 5 attempts
  • Max.Init.Retransmits: 8 attempts
  • Valid.Cookie.Life: 60 seconds (range: 1-60 seconds)

15.4. Heartbeat Parameters​

  • Heartbeat.Interval: 30 seconds (configurable: 10-60 seconds)
  • Heartbeat.Max.Burst: 1

15.5. Delayed Acknowledgement​

  • SACK.Delay: 200 ms (maximum: 500 ms)
  • SACK.Freq: Send SACK every 2 packets

15.6. Congestion Control​

  • Initial cwnd: min(4 * MTU, max(2 * MTU, 4380 bytes))
  • Initial ssthresh: Peer's advertised receiver window (a_rwnd)
  • Max.Burst: 4 PMTU-sized packets
  • Minimum cwnd: 1 * MTU

15.7. Stream and Queue Parameters​

  • MIS (Maximum Inbound Streams): 65535 (maximum)
  • OS (Outbound Streams): 10 (default) or application-specific

15.8. Buffer Sizes​

  • Receive Window: At least 64KB, optimal: Bandwidth-Delay Product (BDP)
  • Send Buffer: At least same as receive window

15.9. Path MTU Discovery​

  • Initial PMTU: IPv4: 576 bytes (conservative) or 1500 bytes (Ethernet); IPv6: 1280 bytes
  • PMTU Probe Interval: 10 minutes

15.10. Timers​

  • T1-init, T1-cookie, T2-shutdown: Initial: RTO.Initial, Max: RTO.Max, exponential backoff
  • T3-rtx: Per-destination RTO, dynamically adjusted

15.11. Parameter Tuning Recommendations​

High-Latency Networks​

  • Increase RTO.Initial: 5-10 seconds
  • Increase Heartbeat.Interval: 60 seconds
  • Increase Receive Window: Based on BDP
  • Increase Max.Burst: 6-8 packets

Low-Latency Networks​

  • Reduce SACK.Delay: 50-100 ms
  • Reduce Heartbeat.Interval: 10-15 seconds

Lossy Networks​

  • Increase Path.Max.Retrans: 7-10
  • Increase Association.Max.Retrans: 15
  • More frequent heartbeats: 15-20 seconds

Mobile/Wireless Networks​

  • Increase RTO.Initial: 5 seconds
  • Increase all retransmission limits
  • Aggressive heartbeats: 10-15 seconds

Summary​

Key Points: These are recommended values, not mandatory; implementations can adjust based on environment; provide configuration interfaces; validate in production.

Tuning Principles: Start with recommended values, monitor performance, adjust gradually, document changes, validate in production environment.

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