by ITU-T is called XG-PON, ITU-T G.987.1 [11], with 10 Gbit/s in downlink and 1 Gbit/s in uplink, 4 QoS for Fixed Ultra-Broadband Table 4.4 PON standards. Maximum bitrate (Gbit/s) Transmission Standard Ethernet, ATM, TDM ITU-T G.984 NG-PON1 TDM, TWDM ITU-T G.987 ITU-T G.9807 NG-PON2 TDM, TWDM ITU-T G.989 1G-EPON Ethernet IEEE 802.3ah 10G-EPON Ethernet IEEE 802.3av ATM, Asynchronous Transfer Mode; EPON, Ethernet PON; NG-PON, Next Generation PON; PON, Passive Optical Network; TDM, Time Division Multiplexing; TWDM, Time and Wavelength Division Multiplexing. and XGS-PON with symmetrical 10 Gbit/s access in both directions (these standards are referred to as NG-PON1), and further toward the next-generation 40 Gbit/s capable PON (i.e. XLG-PON, also referred to as NG-PON2), ITU-T G.989 standard [12]. The NG-PON3 is targeted to provide bitrates up to a maximum 100 Gbit/s. Besides the ITU, the IEEE also standardizes the PON, based on use of Ethernet tech- nology. Hence, its standards are called Ethernet PONs (EPONs). The first such IEEE standard is 1G-EPON (or shortly, EPON), with symmetrical access of 1 Gbit/s in both directions. The next IEEE PON standard is 10G-EPON, which provides bitrates of up to 10 Gbit/s [13]. Similar to the ITU's work on PON, the third PON standard in the 2020s will be 25/50/100G-EPON (IEEE 802.3ca), aiming to provide bitrates gradually up to 100 Gbit/s [14]. 4.3 QoS for Fixed Ultra-Broadband Access Fixed broadband and ultra-broadband access networks are based on three main deploy- ment approaches: DSL, cable, or optical access. In the previous subsection we intro- duced the main characteristic regarding network architectures as well as theoretical bitrates (in downlink and uplink) for each of the three main fixed access technology "groups." In this subsection the focus is more on the QOS solutions applied in the access part of each of the three types of fixed broadband access networks. 4.3.1 QoS for DSL Access DSL technologies appeared in the 1990s and made progress in the 2000s, at a time in th