Precision Time Protocol IEEE1588v2 TICTOC BOF IETF Prague 2007 Ron Cohen Resolute Networks

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 in Vienna Products: Microprocessors, GPS Linked Clocks, Boundary Clocks, NIC Cards, Protocol Stacks, RF Instrumentation, Aircraft Flight Monitoring Instruments, etc. Information: Version 2 PAR approved March 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 Boundary ClockE2E TCP2P TC ClockSynchronizedSyntonized Topology limitations None Homogenous* with 1:1 connection each link State maintained Per port state Per unicast contract state Temporal message state for 2-step TCs Per link state Temporal message state for 2-step TCs Slave scalability HierarchicalMaster sees all slaves Hierarchical (multicast Sync) Linear scalability Control wander accumulation Topology change Measure new delay Pre-compute link delays *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 RequirementsDescription ServicesFrequency, Phase, Time and meta-Time services PrecisionNano-seconds accuracy demonstrated Sub nano-seconds granularity IncrementalAdd Transparent clocks or Boundary clocks to improve performance if required in critical junctions PerformanceTelecom grade performance has been demonstrated over non-PTP-aware networks ScalableUse of boundary clocks and/or transparent clocks to scale and maintain performance limits Robust to master failures Smart slaves synchronizing to two domains or two masters in a single domain. Alternate master takes over when master fails Robust to topology changes P2P mechanism allows to pre-compute link-delays to minimize effect of topology change

20 PTP and TICTOC Derived Requirements Description HW friendlyCorrection field is scaled nano-seconds. All computations by transparent clocks are performed on correction field Correction field is in a fixed position from beginning of PTP header Single Timestamp in fixed position immediately after PTP header for master and slave HW setting Heterogonous design options 2-step clocks simplify master designs 1-step transparent clocks do not need to maintain per master-slave message states Slave friendlyTimescale (Timestamps) is continuous. Timestamps do not jump or miss one second when leap event occurs Time-stamps do not roll over

Questions? Ron Cohen Resolute Networks

22 NTP message format