This turns on detailed Network Data Collection statistics gathering for this specific PVC on its I/O module, but because NDC monitoring consumes per-card resources, the switch enforces hard caps on how many PVCs per interface type can have it enabled simultaneously, 30 on a DS3, 90 on OC3, 360 on OC12. An admin wanting granular historical statistics on a premium customer's circuit would enable cktNdcEnable on it, but needs to track how many other PVCs on the same interface already have it enabled to avoid hitting that card's monitoring limit. For example, on a DS3 interface already running NDC on 30 PVCs, an admin trying to enable cktNdcEnable on a 31st circuit would find the request rejected until they free up a monitoring slot by disabling NDC on another circuit on that same interface.