RFC 7623 describes two types of B-MAC assignments that a PE can implement:
Shared B-MAC addresses that can be used for single-homed CEs and a number of multi-homed CEs connected to Ethernet-Segments.
Dedicated B-MAC addresses per Ethernet-Segment.
In this document and in 7750 SR, 7450 ESS, and 7950 XRS terminology:
A shared-bmac (in IETF) is a source-bmac as configured in service>(b)vpls>pbb>source-bmac
A dedicated-bmac per ES (in IETF) is an es-bmac as configured in service>pbb>use-es-bmac
B-MAC selection and use depends on the multi-homing model; for single-active mode, the type of B-MAC impacts the flooding in the network as follows:
All-active multi-homing requires es-bmacs.
Single-active multi-homing can use es-bmacs or source-bmacs.
The use of source-bmacs minimizes the number of B-MACs being advertised but has a larger impact on C-MAC flush upon ES failures.
The use of es-bmacs optimizes the C-MAC flush upon ES failures at the expense of advertising more B-MACs.