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Synchronization and Redundancy
Synchronous Ethernet
Synchronous Ethernet allows operators to gracefully integrate existing systems and future
deployments into conventional industry-standard synchronization hierarchy. The concept behind
synchronous Ethernet is analogous to SONET/SDH system timing capabilities. It allows the
operator to select any (optical) Ethernet port as a candidate timing reference. The recovered timing
from this port will then be used to time the system (for example, the CPM will lock to this
provisioned reference selection). The operator then could ensure that any of system output would
be locked to a stable traceable frequency source.
Synchronous Ethernet Process
The Ethernet Synchronous process will be implemented in the following manner:
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For Ethernet signal clock recovery, the performance complies to:
→ ANSI ST3 or ETSI/ITU g.813.
→ Using an outboard oscillator. This oscillator is centralized on the CPM/SFM and
serves as the system holdover time-base.
The system clock recovery circuitry can be slaved to either:
→ An optical Synchronous Ethernet input signal.
→ An external BITS/SSU clock with SSMs.
→ A SONET/SDH POS line signal with SSM.
The recovered clock signal is passed to a central system distribution point (on the CPM)
for system-wide distribution.
→ This central distribution point then drives the physical layer timing to all ports on the
node, specifically any Ethernet enabled ports and/or SDH/SONET ports.
The recovered clock signal allows switching between at least two references, the primary
and secondary.
→ Where it is not specified where the switching is performed it is assumed that the CPM
is the likely place. The determination shall be made so that it minimizes the time to
detect and switch between the any of the three states, in the following order: primary,
secondary, and holdover.
7710 SR OS Basic System Configuration Guide
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