Analysis of the Gated IPACT Scheme for EPONs

Interleaved Polling with Adaptive Cycle Time (IPACT) is one of the earliest proposed polling schemes for dynamic bandwidth allocation in Ethernet Passive Optical Networks (EPONs) and has been extensively used as a benchmark by many subsequent allocation schemes. In this paper, we attempt to construct a mathematical model of the IPACT scheme under the gated service discipline. For N = 1 ONU, we derive closed-form expression for the steady state grant size. For N > 1 ONUs, we need to consider separately a small and a large load-distance ratio. For the former case, the N = 1 ONU model holds even for N > 1. For the latter case, we find a closed form expression for the grant size. Our model shows a reasonable match with the values obtained from simulation for the steady state queue size and hence the throughput and delay.