This is the second backward-direction traffic parameter, representing the Committed Burst size (Bc) in the return direction, mirroring circuitFwdTDParam2 but applied independently to backward traffic. This determines how much burst tolerance the return path has before traffic is treated as exceeding its committed rate, which can be tuned separately from the forward burst tolerance for asymmetric traffic patterns. For example, a circuit carrying mostly small acknowledgment traffic in the backward direction might have this set much lower than the forward Bc, since large bursts aren't expected on the return path.