This sets which of three priority tiers this circuit's traffic is queued and forwarded at when there's contention for trunk or port bandwidth, directly affecting how well this circuit's frames survive congestion relative to others sharing the same link. An admin would set voice or premium data circuits to priority 1 and bulk or best-effort circuits to priority 3, so that during a trunk overload low-priority circuits are the ones that lose frames first. For example, raising cktPriority from 3 to 1 on a customer's PVC that keeps complaining about jitter moves its frames ahead of best-effort traffic during congestion.