Enhanced NTP IETF – TicToc BOF Greg Dowd – Jeremy Bennington –

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 A Brief History of NTP 1985 NTPv0 (RFC 958) NTP Packet Header, offset & delay calculation 1988 NTPv1 (RFC 1059) Comprehensive specification of protocol and algorithms Client and server, symmetric operational modes 1989 NTPv2 (RFC 1119) NTP Control Message Protocol (Management of clients) Support for cryptographic authentication based on 64-bit data encryption Standard (DES) keys 1992 NTPv3 (RFC1305) Current standard 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

4 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 Clock Selection and Clustering Algorithms Combining Algorithm Loop Filter VFO Timestamps Clock Discipline Algorithm

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 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

10 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

11 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

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)