e packet-switching telecom world when ATM and Internet technologies coexisted. Many implementations of DSL access networks at the beginning were based on ATM QoS mechanisms. In ATM access nodes, every ATM permanent virtual circuit (PVC) is assigned a traffic class and a traffic profile. Typically, ATM traffic classes are scheduled by using strict priority. Internet fixed access is inseparably connected to using Ethernet as LAN technology, and in such cases QoS support is not mandatory for all Ethernet 4.3 QoS for Fixed Ultra-Broadband Access implementations. So, specific amendments to the Ethernet standard (IEEE 802.3) should be implemented with the aim to provide QoS traffic differentiation (via its separation into a limited number of classes). In Ethernet, the traffic class is determined on a frame by frame approach (on protocol layer 2) by examining the VLAN tag priority field, which provides eight different priority values. Such values can be mapped into lower number of classes (e.g. 2, 3, or 4), however. One important difference between ATM and Ethernet lies in the possibility of multiplexing multiple Ethernet traffic classes over one VLAN. Meanwhile, single ATM traffic class can be used per single ATM virtual circuit. The QoS in DSL access networks is defined by the lower three layers in the protocol stack: (from the top to the bottom of the stack) the network layer, data-link layer, and physical layer. The network layer is Internet protocol, either IPv4 (as the dominant one in the DSL era) or IPv6 (which is typically considered as an optional for DSL) [15]. The data link layer for the IP traffic is Ethernet or ATM. On the physical layer, physical ports can include Ethernet, as well as ports for PDH and/or SDH interfaces. Considering the QoS approaches in the access part of the DSL network, one may distinguish among the following [15]: ATM-based QoS (on layer 2). This approach was the first phase of QoS for DSL access networks, based on ATM. However, with the aim to transfer IP traffic over ATM, IP QoS (e.g