This read-write integer sets the average frame size, in bytes, that the switch assumes for traffic on this circuit, defaulting to 280 bytes if left unconfigured. Because ATM segments variable-length frames into fixed 48-byte cell payloads, the switch uses this average to estimate cell rates, bandwidth allocation, and buffer sizing for the circuit's traffic contract, so an inaccurate value can cause the switch to under- or over-provision cell-level resources relative to the real frame mix. An admin who knows a circuit mostly carries bulk file-transfer traffic with large 1500-byte frames rather than the 280-byte default would update cktFrameSize to roughly 1500 so bandwidth and buffer calculations match actual usage.