Precision Time Protocol IEEE 1588 v 2 TICTOC

Precision Time Protocol IEEE 1588 v 2 TICTOC BOF IETF Prague 2007 Ron Cohen Resolute Networks ronc@resolutenetworks. com

Agenda • • • Status PTPv 1 overview PTPv 2 major additions Transparent clocks PTP and TICTOC 2

The Precision Time Protocol (PTP) • PTPv 1 published in 2002 • Industries involved: v 1: Industrial Automation, T&M, Military, Power Generation and Distribution § v 2 : Audio-Visio Bridges (802. 1 AS), 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: //ieee 1588. nist. gov • Version 2 PAR approved March 2005. Technical work completed 3

PTPv 1 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 4

Protocol overview • Timing Protocol Align slaves to master time § Measure delay between master and slave § Measure per-link delay (v 2) § • Synchronization Hierarchy ‘routing’ Protocol Automatic Best Master Clock Algorithm § Determines the master-slave synchronization clock tree hierarchy § • Management Protocol § Configuration and performance monitoring 5

PTP Master-Slave Hierarchy *Clock symbols taken from ITU-T SG 15 ‘synchronization modeling components – time’ contribution #249 Geneva-2007 by Mike Gilson of BT 6

Timing Protocol Operation 7

Precision using HW time-stamping 8

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

PTPv 2 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/IPv 4&6, Ethernet w/o VLAN, (also Device. Net™, PROFINET, Control. Net™) 10

Sync and Delay-Req formats 11

End-to-End Transparent Clocks E 2 E TCs cancel queuing and processing delays 12

Peer-to-Peer Transparent Clocks P 2 P TCs cancel queuing, processing and propagation delays 13

Peer Delay Measurement (Optional) 14

E 2 E TC Enabled PSN Packet queuing and processing is removed 15

P 2 P TC Enabled PSN Topology change does not effect slave performance 16

Comparison between switches Boundary Clock E 2 E TC P 2 P TC Clock Synchronized Syntonized Topology limitations √ None Homogenous* with 1: 1 connection each link State maintained • • • Temporal message state for 2 -step TCs • • Slave scalability √ Hierarchical Master sees all slaves √ Hierarchical (multicast Sync) Linear scalability Control wander accumulation √ √ Topology change Measure new delay √ Pre-compute link delays Per port state Per unicast contract state Per link state Temporal message state for 2 -step TCs *restriction can be relieved using P-delay over MPLS 17

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 18

PTP and TICTOC Requirements Description Services Frequency, Phase, Time and meta-Time services Precision Nano-seconds accuracy demonstrated Sub nano-seconds granularity Incremental Add Transparent clocks or Boundary clocks to improve performance if required in critical junctions Performance Telecom grade performance has been demonstrated over non -PTP-aware networks Scalable Use 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 P 2 P mechanism allows to pre-compute link-delays to changes minimize effect of topology change 19

PTP and TICTOC Derived Requirements Description HW friendly Correction 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 friendly Timescale (Timestamps) is continuous. Timestamps do not ‘jump’ or ‘miss’ one second when leap event occurs Time-stamps do not roll over 20

Questions? Ron Cohen Resolute Networks ronc@resolute. Networks. com

NTP message format 22