U and DU are integrated at the cell site but the CU is centralized: In this CRAN architecture, the RU and DU are co-located and integrated at the cell site and any front- haul network is local to the site, but the higher-layer functions of the CU are centralized and connected to the DU/RU over a mid-haul network. Scenario 4: The RU, DU, and CU are all in different locations: This is a truly disaggregated CRAN architecture where the RU, the DU, and the CU functions are split over front-haul, mid- haul, and back-haul networks. Backhaul Mobile D-RAN gateways ((2))) Backhaul Mobile Fronthaul C-RAN gateways Midhaul Backhaul Mobile C-RAN gateways ((2))) Fronthaul Midhaul Backhaul Mobile C-RAN gateways Figure 10-29 5G NR CRAN and DRAN Architecture With the introduction of functional splits, there needs to be much more flexibility concerning the types of data being carried through the front-haul (and mid-haul) networks. This change in focus away from a single-use system like CPRI is allowing operators to build packet-based front-haul net- works, using technology such as Ethernet. For this to succeed, CPRI needed to be redefined to use packet-based transport instead of its fixed TDM-like transport. Currently, there are two main standards that defines the packetization of CPRI: Radio over Ethernet (RoE) defines encapsulation and mapping of radio protocols over Ethernet frames. RoE is defined by the IEEE 1914.1 and 1914.3 standards. eCPRI provides an Ethernet- or IP-based front-haul protocol definition between the RU and DU with support for deployment of functional splits. Note the terminology: eCPRI refers to DU functions as the eCPRI Radio Equipment Control (eREC) and refers to the RU functions as eC- PRI Radio Equipment (eRE). Table 10-15 outlines the difference between the CPRI, eCPRI, and RoE protocols. Table 10-15 CPRI Versus eCPRI Versus RoE eCPRI TDM-based design, syn- Packet-based asynchronous protocol Ethernet-based asynchronous protocol chronous protocol Constant data rates, no Variable data rates, sensitive to V