Gigabit-class Passive optical networks (PONs) such as Gigabit PON (G-PON) (/TU-T G.984 series) and JG-Ethernet PON (EPON) (IEEE 802.3ah) are currently being deployed worldwide as the fiber to the premise evolution in the traffic patterns and applications at the access network. Next Generation PONs must be capable of supporting multiple existing and emerging services across multiple market segments, such as consumer, business, and mobile backhaul and therefore requires appropriate traffic management mechanisms. Dynamic Bandwidth Allocation (DBA) can play an effective part in improving the network performance and optimising capacity in the FFTx networks. With the increase in customer base, service providers cannot afford to manually alter the broadband access network characteristics as requirements change. A PON DBA scheme provides the means for upstream traffic control by the Optical Line Terminal (OLT) of Optical Network Units (ONUs). This paper describes the approaches in DBA for PON systems and compares them. The centralised and hierarchical DBA mechanisms are discussed and a DBA that supports universal QoS throughout the PON is deliberated upon.