Interleaved polling with adaptive cycle time

Interleaved Polling with Adaptive Cycle Time (IPACT) is an algorithm designed by Glen Kramer and others at the University of California, Davis. IPACT is a dynamic bandwidth allocation algorithm for use in Ethernet passive optical networks (EPONs).

IPACT uses the Gate and Report messages provided by the EPON Multi-Point Control Protocol (MPCP) to allocate bandwidth to Optical Network Units (ONUs). If the Optical Line Terminal grants bandwidth to an ONU and waits until it has received that particular ONU's transmission before granting bandwidth to another ONU, then time equivalent to a whole messaging round-trip is wasted during which the upstream may remain idle. IPACT eliminates this idle time by sending downstream grant messages to succeeding ONUs while receiving transmissions from previously granted ONUs. It accomplishes this by calculating the time at which a transmission grant allocated to a previous ONU ends.