14.1.3
Best master clock algorithm (BMC)
The
best master clock
(BMC) algorithm performs a distributed selection of the
best candidate clock based on the following clock properties:
l
Identifier
A universally unique numeric identifier for the clock. This is typically
constructed based on a device's MAC address.
l
Quality
Both versions of IEEE 1588 attempt to quantify clock quality based on
expected timing deviation, technology used to implement the clock or
location in a stratum schema, although only V1 knows a data field stratum.
PTP V2 defines the overall quality of a clock by using the data fields
clockAccuracy and clockClass.
l
Priority
An administratively assigned precedence hint used by the BMC to help
select a grandmaster for the PTP domain. IEEE 1588
-
2002 used a single
boolean variable to indicate precedence. IEEE 1588
-
2008 features two
8 bit priority fields.
l
Variance
A clock's estimate of its stability based on observation of its performance
against the PTP reference.
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