This read-write value sets the Sustainable Cell Rate, SCR, for this ATM port, in cells per second, the long-term average rate the traffic contract guarantees, as opposed to the momentary Peak Cell Rate. An admin sets this below the peak rate to define the contracted typical throughput a customer's ATM PVC is provisioned for, with burst behavior beyond SCR governed by lportBurstTolerance. For example, an ATM PVC provisioned with a lportSustCellRate of 1000 cells per second can sustain that rate indefinitely, while momentarily bursting above it, up to the peak rate, only within the allowance defined by the burst tolerance.