Joint IEEE-SA and ITU Workshop on Ethernet
G.8275.x telecom time profiles
Sébastien Jobert
R&D expert, Orange
sebastien.jobert@orange.com
Geneva, Switzerland, 13 July 2013
Why defining time profiles in ITU-T?
New mobile applications requiring
very accurate phase/time sync:
TDD, LTE-A CoMP, MBSFN, locationbased 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
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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
Geneva, Switzerland, 13 July 2013
µs accuracy
µs accuracy
Phase/time
reference
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Architectures & migrations
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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
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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 address
01-80-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
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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)
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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
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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
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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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