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G.8275.x telecom time profiles

Joint IEEE-SA and ITU Workshop on Ethernet. G.8275.x telecom time profiles. Sébastien Jobert R&D expert, Orange sebastien.jobert@orange.com. Why defining time profiles in ITU-T?. New mobile applications requiring very accurate phase/time sync:

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G.8275.x telecom time profiles

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  1. Joint IEEE-SA and ITU Workshop on Ethernet G.8275.x telecom time profiles Sébastien Jobert R&D expert, Orange sebastien.jobert@orange.com

  2. Why defining time profiles in ITU-T? • New mobile applications requiring very accurate phase/time sync: • TDD, LTE-A CoMP, MBSFN, location-based services, … • Cost/vulnerabilities of GNSS systems • Distribution of time sync by the network requested by the operators • Specific telecom requirements led to define PTP telecom profiles in ITU-T

  3. Time sync is critical for MBSFN & CoMP Phase/time reference Phase/time reference µs accuracy µs accuracy • MBSFN or LTE-A CoMP implies that the same content (or synchronized data) is delivered at the same moment by neighbor base stations (to avoid radio inteferences) • If the phase alignment is not good enough, the interferences cannot be handled by cyclic prefix

  4. Architectures & migrations

  5. PTP messages and clocks in G.8275.1 • PTP messages used in the profile: • Sync, Follow_Up, Announce, Delay_Req, and Delay_Resp; Signaling and Management messages are FFS • PTP types of clock used in the profile: • T-GM: master-only Ordinary Clock or master-only Boundary Clock • T-BC: Boundary Clock • T-TSC: slave-only Ordinary Clock • Transparent Clocks for future versions

  6. PTP modes used in G.8275.1 • Two-way mode only • One-step & two-step clocks supported • Ethernet multicast mapping (Annex F) • non-forwardable multicast address01-80-C2-00-00-0E and forwardable multicast address 01-1B-19-00-00-00 • IP mapping is under study • Message rates: 16 pps for Sync and Delay_req, 8 pps for Announce • Combination with SyncE is possible

  7. Alternate BMCA in G.8275.1 • Two modes are possible: • Fully automatic topology setup (similar to IEEE1588v1 BMCA) • Semi-automatic topology setup (in line with G.781 principles – use of Quality Levels and local priorities) • G.8275.1 allows having multiple masters active at the same time • Some PTP attributes unused (Priority1)

  8. Insights to G.8275.2 • G.8275.2 planned to cover “partial timing support” scenarios • Important use case: use of leased lines without synchronization time service Figure from G.8275

  9. PTP modes envisaged in G.8275.2 • Two-way mode • IP mapping has been agreed • Message rates: likely to be higher than in G.8275.1 • Packet selection will be performed in the T-BC and T-TSC, in order to filter traffic load-related PDV and asymmetry • BMCA topic has not yet been discussed • Transparent Clocks may be considered

  10. Conclusion • G.8275.x time PTP telecom profiles are designed to support the needs of current and future mobile technologies • G.8275.1 (full timing suport) will be finalized soon, G.8275.2 (partial timing support) is just starting

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