in old telephone systems - POTS). In addition, an XG-PON provides access to carrier-grade Metro Ethernet services, such as P2P, P2MP, and rooted-multipoint Ethernet virtual connections (EVCs) services, also known as E-Line, Ethernet LAN (E-LAN), and E-Tree [11], as defined by the Metro Ethernet Forum (MEF). The heterogeneous services provided via optical access networks such as PON require QoS support and hence certain traffic management mechanisms. Regarding QoS, XG-PON (i.e. NG-PON1) and NG-PON2 support POTS voice quality with guaranteed fixed bandwidth, low delay, and low jitter required for voice services. In that manner, NG-PON technologies are developed to provide TDM services (e.g. for business customers), and mobile backhauling applications with low delay and jitter as well as guaranteed bandwidth. Because the typical telecom operators' offers to both individual (i.e. residential) and business customers are targeted at provision of VoIP (as a PSTN replacement), IPTV (as a TV replacement), ultra-broadband Internet access (based on network neutrality and best effort principles), and VPNs as leased lines replacement for business users, NG-PON needs also to support at least four classes of services (and should support six classes) and to appropriately map each of the user-to-network interface (UNI) flows. The QoS requirements regarding the number of classes and their mapping are set initially for GPON [21], and they continue to be supported in the NG-PONs, which go up to 10 and on longer-term 100 times higher bitrates than GPON, respectively. Further, NG-PON1 and NG-PON2 also support different mixes of both consumer and business users within a multiple subscriber ONT/ONU, that is, a mix of bitrate-based (e.g. with traffic policing, traffic shaping, etc.) and priority-based traffic management mechanisms within a single ONT/ONU on the same optical network. NG-PON tech- nologies also provide support for VLAN services, including N: 1 and 1:1 VLANs, as well as business Ethernet services on the PON. Initially only 