Transcript Document

Enhanced NTP
IETF – TicToc BOF
Greg Dowd – [email protected]
Jeremy Bennington – [email protected]
Agenda
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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
NTPv0
NTPv1
NTPv2
NTPv3 (RFC1305)
NTPv4
(RFC 958)
(RFC 1059)
(RFC 1119)
Current
standard
(in development)
Stable but not yet
formalized in an
RFC
1985
1988
1989
1992
2006
NTP Packet Comprehensive
specification
Header, offset
of protocol
& delay
and algorithms
calculation
Client and
server,
symmetric
operational
modes
NTP Control
Message
Protocol
(Management
of clients)
Support for
cryptographic
authentication
based on
64-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
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NTP Operations
Peer 1
Filter 1
Peer 2
Filter 2
Peer 3
Filter 3
Clock
Selection
and
Clustering
Algorithms
Clock Discipline Algorithm
Combining
Algorithm
Timestamps
NTP Messages
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Loop Filter
VFO
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
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What’s Different from traditional NTP?
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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
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What stays the same? – NTP on the wire protocol
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eNTP Initial Testing
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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.
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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:
TDEV Performance Results
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
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
Normal TDEV
suggest failed
client
operation
SSUs can be time synchronized
using eNTP over a WAN to
PRC/PRS levels
eNTP performs similar to PTP
Potential
Stability Floor
(minTDEV)
eNTP can be used with OCXO &
VCXO to sub-microsecond time
synchronization
Client Runs
1,2
MTIE Performance
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Summary
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Current NTP is mature, ubiquitous and extensible
Extensions can be backward compatible with existing NTP
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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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