EXFO FTB/IQS-88000 Series Power Blazer for FTB-2/2Pro/500/IQS-600 - Manual (Page 634)

Glossary
622 FTB/IQS-88000 Series
SyncE
In order for an Ethernet interface to be considered Synchronous Ethernet
compliant it needs to be upgraded as shown in the following diagram. In
addition to supporting the ESMC channel, this upgrade consists in allowing
the recovered clock from the CDR to be propagated to a function called the
Ethernet Equipment Clock (EEC).
The EEC is present in a network element (NE) to determine which port
should be used to distribute the frequency to other port(s) in the NE as well
as what QL value to transmit over the ESMC to other network element in
the network synchronization chain. The actual selection decision is based
on the QL value received from the various port(s) in the NE. If none are
valid the EEC is equipped with a better oscillator than a standard Ethernet
interface to provide synchronization (Holdover mode). Typically the
highest QL value is selected among the nominated sources within the
network element.