Best Master Clock Algorithm
The best master clock (BMC) algorithm performs a distributed selection of the best candidate clock based on the following clock properties.
- Identifier - A universally unique numeric identifier for the clock. This is typically constructed based on a device's MAC address.
- 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.
- 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.
- Variance - A clock's estimate of its stability based on observation of its performance against the PTP reference.
IEEE 1588-2008 uses a hierarchical selection algorithm based on the following properties in the order indicated.
- Priority 1
- Class
- Accuracy
- Variance
- Priority 2
- Unique identifier (tie breaker)
IEEE 1588-2002 uses a selection algorithm based on similar properties.
Read more about this topic: Precision Time Protocol
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