Synchronous Ethernet - Nokia 7210 Configuration Manual

System Management

6.5.6 Synchronous Ethernet

Traditionally, Ethernet-based networks employ a physical layer transmitter clock
derived from an inexpensive +/-100ppm crystal oscillator and the receiver locks onto
it. Because data is packetized and can be buffered, there is no need for long-term
frequency stability or for consistency between frequencies of different links.
Synchronous Ethernet is a variant of the line timing that derives the physical layer
transmitter clock from a high-quality frequency reference, replacing the crystal
oscillator with a frequency source traceable to a primary reference clock. This
change is transparent to the other Ethernet layers and does not affect their operation.
The receiver at the far end of the link is locked to the physical layer clock of the
received signal, and ensures access to a highly accurate and stable frequency
reference. In a manner analogous to conventional hierarchical master-slave network
synchronization, this receiver can lock the transmission clock of other ports to this
frequency reference, and establish a fully time-synchronous network.
Unlike methods that rely on sending timing information in packets over an unclocked
physical layer, Synchronous Ethernet is not affected by impairments introduced by
higher levels of networking technology (packet loss, packet delay variation). The
frequency accuracy and stability in Synchronous Ethernet typically exceeds
networks with unsynchronized physical layers.
Synchronous Ethernet allows operators to gracefully integrate existing systems and
future deployments into a conventional industry-standard synchronization hierarchy.
The concept is analogous to SONET/SDH system timing capabilities. The operator
can select any (optical) Ethernet port as a candidate timing reference. The recovered
timing from this port is used to time the system (for example, the CPM will lock to this
provisioned reference selection). The operator then can ensure that all system
output is locked to a stable traceable frequency source.
Note:
276
• The use of Synchronous Ethernet as a candidate reference and for distribution of
recovered reference is supported on all 7210 SAS platforms as described in this
document, except those operating in standalone-VC mode.
• Synchronous Ethernet using fiber Ethernet ports, including 10G and 100G (if
available), is supported on all 7210 SAS platforms as described in this document,
except those operating in standalone-VC mode.
• Please ensure that the SFP or XFP or SFP+ parts used with the SFP, XFP, and SFP+
ports support Synchronous Ethernet.
• Synchronous Ethernet is not supported on virtual chassis (VCs).
Use subject to Terms available at: www.nokia.com
7210 SAS-M, T, R6, R12, Mxp, Sx, S Basic System
© 2021 Nokia.
Configuration Guide
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