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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
1985
NTPv0(RFC 958)
NTP Packet Header, offset
& delay calculation
1988
NTPv1 (RFC 1059)
Comprehensive specificationof protocol
and algorithms
Client and server,
symmetric operational
modes
1989
NTPv2 (RFC 1119)
NTP Control MessageProtocol
(Management of clients)
Support for cryptographic authentication
based on64-bit data encryption Standard
(DES) keys
1992
NTPv3 (RFC1305)
Currentstandard
Improve stability and
accuracy (new algorithm)
Broadcast operational
mode
2006
NTPv4(in development) Stable but not yet formalized in an
RFC
Support of security features
Support of automatic
configuration
Algorithm improvements (Performance)
Backward compatible with
NTPv3
Significant revision of NTPv3
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NTP Operations
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)
NTP Messages
Peer 1
Peer 2
Filter 1
Peer 3
Filter 2
Filter 3
ClockSelection
andClusteringAlgorithms
CombiningAlgorithm
Loop Filter
VFOTimestamps
Clock Discipline Algorithm
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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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Initial Test Environment
TimeMonitor
XLi PDV
Analysis
NTPCarrier-Class
Client
100BaseT Link1588 Protocol
IP Traffic Generators SmartBits, IneoQuest
NTP Carrier-Class
Sync Output
XLi Timestamper
NTP Carrier-Class
Server
Traffic AnalyzersIneoQuest
Optional Routers and Swtiches to increase hop count
XLi PDV
Analysis
XLi
Timestamper
GPS Reference
GPS Reference
GPS Reference
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Baseline Test Results
Summary
Client meets G.811 and GR2830 stratum 1 performance under baseline case.
MTIE Performance Results
TDEV Performance Results
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
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Loading Test Example Configuration
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
TDEV std window
averaging
TDEV window floor
modification
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Loaded Test Results
TDEV Performance
MTIE Performance
Client Runs 1,2
Potential Stability Floor (minTDEV)
Normal TDEV suggest failed
client operation
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
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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)
