1. 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
Geneva, Switzerland, 13 July 2013

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
Geneva, Switzerland, 13 July 2013

3. Time sync is critical for MBSFN & CoMP
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
Phase/time reference
µs accuracy
Geneva, Switzerland, 13 July 2013

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
Geneva, Switzerland, 13 July 2013

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

7. Two modes are possible:
Alternate BMCA in G
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 allows having multiple masters active at the same time
Some PTP attributes unused (Priority1)
Geneva, Switzerland, 13 July 2013

8. G.8275.2 planned to cover “partial timing support” scenarios
Insights to G
G planned to cover “partial timing support” scenarios
Important use case: use of leased lines without synchronization time service
Figure from G.8275
Geneva, Switzerland, 13 July 2013

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
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
Geneva, Switzerland, 13 July 2013

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