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Enhanced NTP: Achieving Higher Accuracy and Performance

Explore the enhanced NTP protocol, its differentiators, improvements, and benefits in achieving higher accuracy and transaction rates. Learn about stratum 1 availability, new client servo classes, and the potential for sub-microsecond time synchronization.

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Enhanced NTP: Achieving Higher Accuracy and Performance

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  1. Enhanced NTPIETF – TicToc BOF Greg Dowd – gdowd@symmetricom.comJeremy Bennington – jbennington@symmetricom.com

  2. 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

  3. NTPv0 (RFC 958) NTPv1 (RFC 1059) NTPv2 (RFC 1119) NTPv3 (RFC1305) Currentstandard NTPv4(in development) Stable but not yet formalized in an RFC 1988 1989 1992 2006 1985 NTP Packet Header, offset & delay calculation Comprehensive specificationof protocoland algorithms Client and server, symmetric operational modes NTP Control MessageProtocol (Management of clients) Support for cryptographic authentication based on64-bit data encryption Standard (DES) keys Improve stability and accuracy (new algorithm) Broadcast operational mode Support of security features Support of automatic configuration Algorithm improvements (Performance) Backward compatible with NTPv3 Significant revision of NTPv3 A Brief History of NTP

  4. NTP Operations Peer 1 Filter 1 Clock Selection and Clustering Algorithms Clock Discipline Algorithm • 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) Combining Algorithm Peer 2 Filter 2 Loop Filter Peer 3 Filter 3 Timestamps VFO NTP Messages

  5. Enhanced NTP (eNTP) Differentiators • What’s 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

  6. 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)

  7. 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

  8. Initial Test Environment

  9. 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 < 0.1 of 1C/60s LO: Stratum 2 Servo: Lite Hybrid Packet Client Update Rate: 64Hz TDEV Performance Results

  10. 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 < 0.1 of 1C/60s LO: Stratum 2 Servo: Lite Hybrid Packet Client Update Rate: 16 Hz

  11. 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

  12. 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)

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