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Enhanced NTP IETF – TicToc BOF. Greg Dowd – [email protected] Jeremy Bennington – [email protected] 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

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Enhanced ntp ietf tictoc bof l.jpg

Enhanced NTPIETF – TicToc BOF

Greg Dowd – [email protected] Bennington – [email protected]


Agenda l.jpg
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


A brief history of ntp l.jpg

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


Ntp operations l.jpg
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


Enhanced ntp entp differentiators l.jpg
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


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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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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


Slide10 l.jpg

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


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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)


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