Digital Instruments SYNC-SWITCH User Manual page 16

SYNC-SWITCH - MANUAL
Clock quality level indication is carried via an Ethernet Synchronization Messaging Channel (ESMC) protocol
running over the synchronous Ethernet link.
A "heart-beat" message is used to provide a continuous indication of the SSM clock quality level every
•
second.
An event message with the new SSM value is generated immediately.
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If no SSM messages are received after a five second period the SSM value is set to DNU (Do Not Use).
The SSM code contained in the ESMC PDU represents the free-run accuracy of the clock source of the synchronization
trail.
When no valid SyncE source is provided the switch clock runs in free run. Its voltage control may be fine tuned with the
vtune value.
SYNC-SWITCH is capable to enter holdover after 1.6 µs the cable loss is recognized, thus providing a great phase
locking performance.
In order to check that the Synchronous Ethernet feature is properly working is possible to analyze the Ethernet traffic
with a Network Protocol Analyzer (e.g. Wireshark
correct SSM code.
The performance of the PTP protocol is greatly affected by the Packet Delay Variation (PDV).
The purpose of a Transparent Clock is to record the ingress and egress time of traversing PTP messages and alter the
PTP correction field accordingly, so that the PTP performance is less subject to network load.
SYNC-SWITCH is able to apply such correction on the fly without requiring additional packets in a way that is
completely transparent to the other PTP devices.
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http://www.wireshark.org/
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SYNC-SWITCH – Manual – Rev 1.1
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) and verify that ESMC packets are being propagated with the
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