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Precision Time Protocol

Precision Time Protocol. IEEE1588v2 TICTOC BOF IETF Prague 2007 Ron Cohen Resolute Networks ronc@resolutenetworks.com. Agenda. Status PTPv1 overview PTPv2 major additions Transparent clocks PTP and TICTOC . The Precision Time Protocol (PTP). PTPv1 published in 2002

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Precision Time Protocol

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  1. Precision Time Protocol IEEE1588v2 TICTOC BOF IETF Prague 2007 Ron Cohen Resolute Networks ronc@resolutenetworks.com

  2. Agenda • Status • PTPv1 overview • PTPv2 major additions • Transparent clocks • PTP and TICTOC

  3. The Precision Time Protocol (PTP) • PTPv1 published in 2002 • Industries involved: • v1: Industrial Automation, T&M, Military, Power Generation and Distribution • v2 : Audio-Visio Bridges (802.1AS), Telecom and Mobile • Symposia in 2003, 2004, 2005, and 2006. 2007 in Vienna • Products: Microprocessors, GPS Linked Clocks, Boundary Clocks, NIC Cards, Protocol Stacks, RF Instrumentation, Aircraft Flight Monitoring Instruments, etc. • Information: http://ieee1588.nist.gov • Version 2 PAR approved March 2005. Technical work completed

  4. PTPv1 objectives • Sub-microsecond synchronization • Intended for relatively localized systems • Applicable to networks supporting multicast • Simple, administration free installation • Support heterogeneous systems of clocks with varying precision, resolution and stability • Minimal resource requirements on networks and host components

  5. Protocol overview • Timing Protocol • Align slaves to master time • Measure delay between master and slave • Measure per-link delay (v2) • Synchronization Hierarchy ‘routing’ Protocol • Automatic Best Master Clock Algorithm • Determines the master-slave synchronization clock tree hierarchy • Management Protocol • Configuration and performance monitoring

  6. PTP Master-Slave Hierarchy *Clock symbols taken from ITU-T SG15 ‘synchronization modeling components – time’ contribution #249 Geneva-2007 by Mike Gilson of BT

  7. Timing Protocol Operation

  8. Precision using HW time-stamping

  9. 1-step and 2-step clocks • 1-step clock updates accurate timestamp (t1) in Sync message • 2-step clock sends accurate timestamp (t1) in a Follow_Up message • Simplify design while avoiding queuing noise • Ease integration of security extensions

  10. PTPv2 major additions • Synchronization accuracies better than 1 nanosecond • Higher sampling/message rates • Unicast communication • Correction for asymmetry • Transparent clocks • Redundancy • Configurable synchronization hierarchy • Decouple sync messaging from hierarchy signaling • Formal mechanisms for message extensions • Mappings to UDP/IPv4&6, Ethernet w/o VLAN, (also DeviceNet™, PROFINET, ControlNet™)

  11. Sync and Delay-Req formats

  12. End-to-End Transparent Clocks E2E TCs cancel queuing and processing delays

  13. Peer-to-Peer Transparent Clocks P2P TCs cancel queuing, processing and propagation delays

  14. Peer Delay Measurement (Optional)

  15. E2E TC Enabled PSN Packet queuing and processing is removed

  16. P2P TC Enabled PSN Topology change does not effect slave performance

  17. Comparison between switches *restriction can be relieved using P-delay over MPLS

  18. PTP protocol extensions • Define a profile that selects optional feature set, default and range of values • Define TLV extension to messages • Define flag-fields to be carried in event messages • Define alternate management scheme (SNMP) • Define alternate synchronization hierarchy selection (routing) algorithm • Define additional transport mapping (PTP over MPLS) • Define alternate clock quality levels and attributes

  19. PTP and TICTOC

  20. PTP and TICTOC

  21. Questions? Ron Cohen Resolute Networks ronc@resoluteNetworks.com

  22. NTP message format

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