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Long-Reach Passive Optical Network (LRPON) technology seems to be a strong candidate for next generation optical access networks. LRPON aims to combine the advantages of optical metro and access networks before the backbone by offering long feeder distance and high split ratio. On the other hand, long feeder distance causes long propagation delay while together with high split ratio they lead to longer packet delay. In order to decrease packet delay, we have recently proposed a QoS-aware bandwidth allocation scheme which is called as Periodic Gate Optimization with QoS-awareness (PGO-QoS). This scheme is based on multi-threaded MPCP that has been previously proposed in the literature. In this paper, we briefly present PGO-QoS and discuss the impacts of buffer size on its performance under a feeder distance of 100 km. We show that PGO-QoS leads to shorter average delay than multi-threaded MPCP while slightly decreasing the packet loss ratio. As expected, larger buffer size increases the packet delay, especially under heavy loads. However, changing the buffer size does not affect the relative performance of PGO-QoS to the multi-threaded MPCP. Furthermore, we evaluate the effects of pre-specified delay bounds on the performance of PGO-QoS where each ONU runs an estimation to determine whether an incoming packet can reach the OLT within its delay bound.