 operators (which use access networks with DOCSIS) to define policies on aggregated service flows. It is based on a strict hierarchical approach, where the available total channel capacity is the root and each "child" node can have only one parent node (that means the term "strict" hierarchy). So, one may note that HQoS is in fact a CMTS-only QoS feature because no CMs will be aware of the existence of the HQoS. Regarding the PacketCable part of the cable network architecture, PacketCable 2.0 from CableLabs introduces an IP multimedia subsystem, which is standardized by the 3GPP (3G Partnership Project) [18]. The PacketCable QoS architecture (high-level view) is shown in Figure 4.5. The PacketCable application manager (PAM) receives session-level QoS requests from the IMS. PacketCable 2.0 is designed to perform policy control for access to services by end-users (via their CMs) in the same manner as implemented by the 3GPP the architecture, with PCRF (policy and charging rules function) node between the CMTS system on one side (the cable network access) and the IMS on the other (the telecom operator's core network). 4.3.3 QoS for PON Access For QoS support the same approaches which are network access agnostic are used for PON and GPON as they have been previously defined for DSL access networks and triple play services (voice, TV, and Internet access) by the Broadband Forum [19]. However, GPON technology on the network interface layer is different that of DSL, SO mapping of GPON to Ethernet is required and vice versa. GPON supports two layers of traffic encapsulation [20]: Encapsulation of Ethernet frames into GEM (GPON encapsulation method) frames. Encapsulation of GEM into the GPON transmission convergence (GTC) frame, which includes pure TDM traffic as well as ATM cells which are 53 bytes fixed-length Policy server determines the serving CMTS in the network for a given UE Packetcable Policy server application (proxy) manager Policy decisions are pushed by the policy server onto the CMTS Registration and session