Scheduling Hybrid WDM/TDM EPONs with Heterogeneous Propagation Delays

Dynamic wavelength bandwidth assignment (DWBA) in hybrid TDM/WDM EPON is a challenging and important issue. Normally, the ONUs located at different distances away from the OLT can affect the network performance caused by the heterogeneous round trip delays in report-grant based bandwidth allocation. This paper addresses this problem by mapping the DWBA problem in WDM/TDM EPON into parallel machine scheduling with release dates. This scheduling problem is NP-hard. In order to achieve high network utilization, we try to minimize the cycle length for given traffic loads. We propose hybrid shortest propagation delay (SPD) first and longest processing time (LPT) first (SPD/LPT) scheduling algorithms and analyze their network performances. The results show that our proposed algorithms can achieve the shortest cycle length as compared with traditional LPT and SPD rules when fewer upstream wavelengths are deployed with a give number of ONUs.