This is the reverse-direction counterpart to cktBc, defining the committed burst size for traffic flowing back toward this circuit's originating end, letting the admin configure asymmetric burst tolerances to match an asymmetric CIR set via cktRCir. For example, a circuit with a small cktRCir but a proportionally generous cktRBe/cktRBc combination could still tolerate occasional larger bursts in the lightly-provisioned reverse direction without those bursts immediately being treated as excess.