Priority 802.1p = 4 or 5 downlink) queue Ethernet frame Priority 802.1p = 2 or 3 queue T-CONT (in uplink) Ethernet frame Priority 802.1p = 0 or 1 queue Reserved for operation and maintenance T-CONT 4 Best effort bandwidth Additional Non-assured bandwidth T-CONT 3 bandwidth Assured bandwidth T-CONT 2 Guaranteed bandwidth T-CONT 1 Fixed bandwidth GEM - Generic encapsulation method ONT - Optical network terminal ONU - Optical network unit T-CONT - Transmission container VLAN - Virtual local area network Figure 4.6 Priority scheduling for multiple queues in T-CONT in GPON/NG-PONs. 4.4 QoS in Ethernet and Metro Ethernet In the past, telecom operators' core and transport networks were primarily built on SDH technologies. However, Ethernet as a unified local area network technology since the 1990s has spread to metro and to transport environments, including providers', corporate, and home networks. The organization which supports the expansion of 4 QoS for Fixed Ultra-Broadband Ethernet from LAN to MANs (metropolitan area networks) and further to WAN and international networks is MEF. In general, Ethernet (IEEE 802.3 standard) has become unified LAN due to lower cost of the equipment, lower operation and maintenance costs, and dedication to transport IP packets on the network layer. In general, IEEE is developing Ethernet standards on physical and data-link protocol layers. Initially Ethernet has no QoS built-in and no TDM support such as legacy telecommunication networks for transport of voice services (e.g. PSTN/ISDN). With moving to Carrier Ethernet (that is, Ethernet for telecom operators), certain end-users are demanding the same level of performance that they had in the past with TDM-based WAN [24]. The evolution of Ethernet toward service providers' requirements and telecom oper- ators' networks has led to the MEF's definition of "Metro Ethernet network" or "Carrier Ethernet" (the names are interchangeable). For the development of Carrier Ethernet, the requirements were to provide network scalability, QoS for dif