Enhanced%20NTP%20IETF%20

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Enhanced NTP IETF TicToc BOF
Greg Dowd gdowd_at_symmetricom.comJeremy
Bennington jbennington_at_symmetricom.com
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Agenda

• Premise Higher Accuracy can be achieved though
  optional enhancements to NTP
• Quick Review of NTP
• Enhanced NTP Differentiators
• Stratum 1 (G.811 GR2830) Initial Testing
• Example of new Servo Loop
• Summary

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A Brief History of NTP
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NTP Operations
Peer 1
Filter 1
Clock Selection and Clustering Algorithms
Clock Discipline Algorithm
Combining Algorithm
Peer 2
Filter 2
Loop Filter
Peer 3
Filter 3
VFO
Timestamps
NTP Messages

• Complex algorithms to improve accuracy of
  estimated delays and offsets
• Clock adjust process runs at 1s interval to
  amortize corrections in small adjustments
• Polling algorithm
• Filtering algorithm
• Clock selection and clustering algorithms
• Combining algorithms
• Loop filter and variable frequency oscillator
  (VFO)

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Enhanced NTP (eNTP) Differentiators

• Whats Different from traditional NTP?
• TimeStamp Accuracy constrained to specified
  levels
• On the Fly Methods
• Gating Methods
• Error Feedback Mechanisms
• Stratum 1 Availability High availability/capacity
  of stratum 1 sources
• Higher Transaction Rates Servers support both
  existing and higher demand clients
• New Client Servo Classes to support carrier
  requirements such as stratum 1 (G.811, GR2830)
  performance
• What stays the same? NTP on the wire protocol

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eNTP Initial Testing

• Following Differentiators Enabled
• Server Time Stamp Accuracy constrained to
  nanosecond levels
• Stratum 1 Availability Server operating with GPS
  traceability verified with Lab Cesium standard.
• Higher Transaction Rates Servers operating up to
  64 transactions per second
• New Client Servo Class Lite version of hybrid
  packet client algorithm (see description later)

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Initial Test Environment

• Primary Objective Evaluate with respect to
  stratum 1 (G.811,GR2830) grade synchronization
  using carrier class NTP over managed IP network.
• Lab Network constrained to managed IP over
  carrier grade routers and switches
• Packet Delay Variation monitored independently at
  ingress and egress during testing.
• G.8261 and extensions used for disturbance
  traffic
• Higher tier (stratum 2, type I) oscillators
• Higher update rates up to 64 Hz

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Initial Test Environment
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Baseline Test Results
MTIE Performance Results
Summary Client meets G.811 and GR2830 stratum 1
performance under baseline case.
Configuration Transport Direct 1Gbps link with
ingress and egress switches. Loading profile No
Load NTP priority best effort UDP Thermal shock
profile benign lab lt 0.1 of 1C/60s LO Stratum
2 Servo Lite Hybrid Packet Client Update Rate
64Hz
TDEV Performance Results
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Loading Test Example Configuration
TDEV std window averaging
TDEV window floor modification
Configuration Transport Two Carrier Grade
Routers (1Gbps links) with ingress and egress
switches. Loading profile G.8261 perturbation
traffic at 60 NTP priority best effort
UDP Thermal shock profile benign lab lt 0.1 of
1C/60s LO Stratum 2 Servo Lite Hybrid Packet
Client Update Rate 16 Hz
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Loaded Test Results
TDEV Performance
Summary SSUs can be time synchronized using eNTP
over a WAN to PRC/PRS levels eNTP performs
similar to PTP eNTP can be used with OCXO VCXO
to sub-microsecond time synchronization
Normal TDEV suggest failed client operation
Potential Stability Floor (minTDEV)
Client Runs 1,2
MTIE Performance
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Summary

• Current NTP is mature, ubiquitous and extensible
• Extensions can be backward compatible with
  existing NTP
• eNTP NTP Clients can be mixed in deployment
• Existing NTP would benefit from reliability
• SW based eNTP could see some performance
  enhancements
• Stratum 1 performance is viable over managed IP
  networks utilizing high quality stratum
  oscillators (distributed S1 NTP via SSUs)
• Sub-Microsecond performance is achievable using
  VCXO and OCXO Clients (also meets G.823/G.824)