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Q13 Activities on Time Synchronization

Joint ITU-T/IEEE Workshop on The Future of Ethernet Transport (Geneva, 28 May 2010). Q13 Activities on Time Synchronization. Jean-Loup Ferrant, Calnex, Q13 Rapporteur Stefano Ruffini Ericsson, Q13 Associated Rapporteur. Transport of frequency in Q13/15. 2.

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Q13 Activities on Time Synchronization

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  1. Joint ITU-T/IEEE Workshop on The Future of Ethernet Transport(Geneva, 28 May 2010) Q13 Activities on Time Synchronization Jean-Loup Ferrant, Calnex, Q13 Rapporteur Stefano Ruffini Ericsson, Q13 Associated Rapporteur

  2. Transport of frequencyin Q13/15 2 • In 2004, Q13 started working on transport of timing on PSN • Interworking with TDM was required • FDD was the mostly deployed mobile technology (only frequency sync required) • Focus on Frequency synchronization • 1- Transport of frequency in CES applications • 2- Transport of frequency via SyncE • First series of recommendations: G.8261, G.8262, G.8264 • Initial discussion on time synchronization • Transport of time on SyncE was also proposed, but 1588 was preferred

  3. Transport of time in Q13/15 3 • Transport of time became important with TDD and new applications (e.g. MBSFN) • Q13 has chosen to focus on 1588-2008 for the transport of time and frequency (NTP also briefly mentioned) • Q13 worked on a first « telecom profile » (consent planned next week) • Q13 workplan has been rearranged to align frequency and time recommendations

  4. Structure of documents in Q13/15 4

  5. Time-Phase Requirements 5

  6. Example in Wireless Application +/- 1.5 ms +/- 1.5 ms +/- 3 ms eNodeB eNodeB • Phase Sync needed to Synchronize transmission from different base stations • To optimize bandwidth usage and enhance network capacity • In TDD mode uplink and downlink are separated in time • LTE-TDD: 3 ms time difference between Base Stations (small cell) • “phase synchronization” requirement of 1.5 ms between the master and the slave, according to ITU-T definitions (see G.8260) 6

  7. G.8271 The G.8271, Time and Phase synchronization aspects in packet networks First Q13 recommendation in the G.827x series; Draft already available Scope Overall performance objectives (see applications in previous slide) Methods to distribute phase synchronization and/or time synchronization (GNSS, Packet-based) Network Model Initial focus: Ethernet physical layer Detailed Network Limits are proposed to be included in a separate document (to be defined, e.g. G.8271.1) 7

  8. IEEE defines a profile as “The set of allowed precision time Protocol (PTP) features applicable to a device” The first purpose of a profile is to allow interworking between PTP master and slaves ITU-T Q13/15 agreed to define telecom profiles based on IEEE 1588-2008 First profiles will address the transport of frequency Next profiles will address the transport of phase, time and frequency IEEE1588 Telecom Profiles 8

  9. Frequency telecom profile 9 • First profile for end to end application, no support from intermediate nodes • Frequency synchronization only • PDV is not controlled in intermediate nodes • Absolute delay is not an issue for frequency • No asymmetry issue • Network architecture as per G.8265

  10. Frequency distribution without timing support from the network (Unicast mode) 10 • Selected options • Unicast is the selected mode • Mix unicast and multicast mode is for further study and may be specified in future profiles • Mapping:IEEE-2008 annexD (UDP over IPV4) • One-way vs two ways • Masters must support both • Slaves may select one • One-step vs two-steps • Both allowed • BMCA (best master clock algorithm) • Definition of a specific BMCA by ITU-T

  11. IEEE1588 Time Profile • The distribution of accurate time/phase (e.g. < 1 microsecond) can be challenging without timing support from the network • PDV impacting accurate frequency distribution • Asymmetry due to different traffic load on forward and reverse direction • Asymmetry due to particular transport technologies • A network with timing support is generally required • E.g. Boundary Clock in every node 11

  12. Related Aspects • Several aspects need to be addressed by Q13 • Telecom Profile (e.g. PTP mapping, Unicast vs. Multicast, packet rate, BMC, etc.) • Is the Transparent Clock allowed in Telecom ? • Performance aspects (e.g. Clock characteristics, Holdover, etc.) • Architecture (e.g. Sync Reference chain), redundancy • Combination with SyncE • Interworking with the access technologies 12

  13. Additional Slides

  14. Phase and Time Relevant Terms are defined in G.8260 Phase: significant events occur at the same instant Time: nodes get information about time and share a common timescale and related epoch Time Phase 14

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