Methods for Improving NTP
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At ITSF 2016 in Prague, Nir Laufer of Oscilloquartz explained how to combine PTP and NTP to help meet the sub-millisecond accuracy needed for many new applications.
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Methods for Improving NTP
- 1. Improving NTP Installed Base Time Accuracy Nov 2016 Nir Laufer , Director PLM ITSF 2016
- 2. © 2016 ADVA Optical Networking. All rights reserved.2 NTP – It's Been Around a While • Network Time Protocol (NTP) is a networking protocol for clock synchronization between computer systems over packet-switched, variable-latency data networks • Invented by Professor David L. Mills in 1981 • NTP is used to deliver time to various applications, including enterprise, financial, telecom, power … In operation since 1985, NTP is one of the oldest internet protocols in current use
- 3. © 2016 ADVA Optical Networking. All rights reserved.3 How Many NTP Clients Are Out There? • MIT research from Dec 1999 estimates the NTP network contains at least 175,000 hosts • Aug, 2005, querying an initial set of 263 public NTP servers - stratum 1 and 2 - listed on NTP Public Services Project - discovered 1,278,834 unique IP addresses • Feb 2016 - Usage analysis of the NIST Internet Time Service identified >220 million unique IPv4 addresses • Overall, a few 100 million!
- 4. © 2016 ADVA Optical Networking. All rights reserved.4 Typical Time Accuracy Achieved by NTP • Highly dependent on NTP server accuracy, network asymmetry, PDV and NTP client implementation • In most cases, 100 microseconds to 100 milliseconds is achievable Reaching microseconds level with existing NTP solutions is challenging!
- 5. © 2016 ADVA Optical Networking. All rights reserved.5 Time Is Money … • SEC Rule 613 issued August 2012 • Requires all actions placed on any US exchange to be recorded to accuracy of at least 1mS • Enables auditing in case of fraud investigation • European Securities and Markets Authority (ESMA) 1464, Sep 2015 and 1464 Annex: • Transactions executed on a trading venue • Activity using high frequency algorithmic trading technique – Clocks synchronized to within 100 uS • Any other trading activity - Clocks synchronized to within 1mS • Many Algo traders want to record transaction times in order to: • Audit the performance of their algorithms and analyze historic data to improve their trading strategies
- 6. © 2016 ADVA Optical Networking. All rights reserved.6 NTP Packet Exchange T1 – Time request sent by the client (using client clock) T2 – Time request received by the server (using server clock) T3 – Time reply sent by the server (using server clock) T4 – Time reply received by the client (using client clock) T2 = T1 + Delay_CS - Offset T4 = T3 + Delay_SC + Offset Symmetry: Delay_CS = Delay_SC = Delay Offset = ((T4-T3)-(T2-T1))/2 Asymmetry: Delay_CS != Delay_SC : Offset+(Delay_CS-Delay_SC)/2=(T4-T3)-(T2-T1))/2 ClientServer Offset from Server T1 T2 Request T3 T4 Reply Delays must be symmetrical and constant – asymmetry and PDV will impact client performance
- 7. © 2016 ADVA Optical Networking. All rights reserved.7 Client MACPHY HW Clock Timestamp SW/Stack Sources of Inaccuracy Server MAC PHY HW Clock Timestamp SW/Stack GNSS • Server time reference inaccuracy • Server internal PDV and asymmetry • Network PDV and asymmetry • Client internal PDV and asymmetry NTP Packets
- 8. © 2016 ADVA Optical Networking. All rights reserved.8 • Use telecom grade NTP server • GNSS as reference with backup options (PTP/Sync-E/BITS) • High end local oscillator for enhanced phase holdover • Meet ITU-T G.8272 PRTC: +/- 100nsec from UTC on PPS & packet interfaces • Use HW based timestamping which eliminate internal PDV and asymmetry • Support high number of transactions per second Client MACPHY HW Clock Timestamp SW/Stack Improving Accuracy – Server Side Server MAC PHY HW Clock Timestamp SW/Stack GNSS Backup NTP Packets
- 9. © 2016 ADVA Optical Networking. All rights reserved.9 • If possible – use HW based timestamping, which eliminates internal PDV and asymmetry • If not possible – optimize the SW design by targeting deterministic delays and delay asymmetries which should be compensated • Increase packet rate Client MACPHY HW Clock Timestamp SW/Stack Server MAC PHY HW Clock Timestamp SW/Stack GNSS Backup Improving Accuracy – Client Side NTP Packets
- 10. © 2016 ADVA Optical Networking. All rights reserved.10 • PTP is the selected solution for delivering time, accurate within sub- microsecond in telecom / power / audio & video applications • Fully standardizes and adopted by operators • Telecom ITU-T G.8275.x • Power IEEE C37.238-2011 • Audio and video profile - IEEE 802.1AS Can PTP Help ? PTP can deliver time within sub-microsecond
- 11. © 2016 ADVA Optical Networking. All rights reserved.11 • PTP accuracy is also affected by PDV & asymmetry but … • The use of PTP aware network elements - boundary clocks (BC) and transparent clocks (TC) can be used to eliminate PDV & asymmetry Can PTP Help ? TCs and BCs are the main advantage of PTP over NTP T-GM GNSS Packet-Based Network PTP Slave BCBC TCTCTCBC PTP Packets
- 12. © 2016 ADVA Optical Networking. All rights reserved.12 Combine PTP with NTP by using PTP BC/TC to overcome PDV and asymmetry Core/Mobile Backhaul Provider High PDV/ AsymmetryNTP Client NTP Server GNSS The Solution NTP NTP NTP Packets
- 13. © 2016 ADVA Optical Networking. All rights reserved.13 Combine PTP with NTP by using PTP BC/TC to overcome PDV and asymmetry NTP Client GNSS The Solution PTP To NTP Core/Mobile Backhaul Provider NTP BCTC PTP Grand Master PTP PTP Packets NTP Packets
- 14. © 2016 ADVA Optical Networking. All rights reserved.14 12:00:00.000 12:00:00.001 12:00:00.002 12:00:01.000NTP 1PPS 1PPS rising edge strobes the value of time delivered by NTP once per second. NTP inherits the accuracy delivered by PTP. NTP NIC with 1PPS I/O Client Server OSA5420 1PPS in NTP High Accuracy PTP Time Service PTP SlaveNTP Server* 32x 1PPS Outputs Concept for Install Base - NTP Server + 1PPS OSA5420 PTP GM
- 15. © 2016 ADVA Optical Networking. All rights reserved.15 • “All in one” Cost effective device which can be a PTP Slave , BC, GM , Probe , NTP server , including PTP to NTP translation • Can support PTP and NTP simultaneously • Can translate from PTP input to NTP output • Include high-quality local oscillator and back up options via Sync- E/BITS • Optimal - Sync-E/BITS/CLK/PPS+ToD fan-out • Sync probing and assurance Equipment Requirements: “All in one” product for all next gen and legacy sync requirements
- 16. © 2016 ADVA Optical Networking. All rights reserved.16 • No standards available but … • PTP deliver information which enable construction of UTC • TAI + UTC offset + Leap second information • Information related to clock quality • clockClass • clockAccuracy • NTP Stratum level • Can be Stratum 2 when locked to partial on path support PTP • Can be Stratum 1 when locked to full on path support PTP PTP to NTP Translation
- 17. © 2016 ADVA Optical Networking. All rights reserved.17 • Time synchronization is required between the source and destination devices in order to provide accurate one-way delay (latency) or delay-variation measurements • Legacy network element are using NTP to create the required common time • Limited accuracy of measurement due to NTP server location Y.1731 Ethernet OAM
- 18. © 2016 ADVA Optical Networking. All rights reserved.18 Example - EOAM NTP Server GNSS EOAM SLA Demarcation point NID (NTP Client) Customer Network Mobile Backhaul Provider EOAM SLA Aggregator NTP High PDV/ Asymmetry
- 19. © 2016 ADVA Optical Networking. All rights reserved.19 Example - EOAM NTP Server GNSS EOAM SLA Demarcation point NID (NTP Client) Customer Network Mobile Backhaul Provider EOAM SLA Aggregator NTP PTP PTP To NTP Converter BCTC
- 20. © 2016 ADVA Optical Networking. All rights reserved.20 • Operators are upgrading their networks in order to deliver accurate phase required for RAN applications (LTE-A/LTE-TDD) • The accurate time delivered via PTP can be translated to NTP and be offered as a service • Such a service can be used to improve installed base NTP clients time accuracy Time as a Service – TaaS (Time is money) Time as a Service – new potential source of revenue
- 21. © 2016 ADVA Optical Networking. All rights reserved.21 Time as a Service Into Data Centre Financial Markets, Health, Media Bring accurate time and frequency into data centers Slave Client Slave Server NICs Customer Rack Data Centre PTP NTP PTP GNSS PTP To NTP Core/Mobile Backhaul Provider BCTC PTP GM PTPPTP & NTP NIC NIC PTP PTP PTP
- 22. © 2016 ADVA Optical Networking. All rights reserved.22 Time accuracy of NTP installed based clients can be improved significantly by combining the following: • Upgrade of NTP servers to telecom grade servers (with +/- 100 nsec on NTP packet interface) • Combine PTP with NTP to overcome asymmetry and PDV • Translation from PTP to NTP should be done as close as possible to NTP clients • Leverage investment made for PTP to improve NTP accuracy – both can be offered as a service (TAAS) Summary
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