fectively deployed in selected situations. Even in situations where the architecture is cost effec- tive, the distance and cost restrictions limit the number of cell sites that can be homed on a single central baseband pooling site. This in turn limits the size of the gains that can be obtained from NFV and SDN and the network cloud architecture. A more recent RAN architecture development is the split RAN (sRAN) architecture, as shown in Figure 11.15. This architecture is being developed to combine the advantages of the cRAN archi- tecture with the cost-effective transport of the dRAN architecture. At the current time, this architec- ture is not yet in widespread deployment-it is at the prototype and development stage. In the sRAN configuration, the hardware and functions of the BBU are decomposed into two separate components shown as BBU part 1 located at the cell site and BBU part 2 located at the central site. The lower layer protocol functions, which are the most sensitive to delay, are located in the part of the BBU located at the cell site, with a CPRI interface running up the cell tower to the RF components. These functions at the cell tower also greatly reduce the data transport require- ments, SO that the link between BBU part 1 at the cell site and BBU part 2 at the central site can be an efficient low latency Ethernet link instead of the CPRI link. These architectures are under devel- opment and evaluation. A key characteristic of these architectures is that the BBU functions must be split between the cell site and the central site. Each function of the BBU needs to be assigned to one of the locations. This leads to a wide variety of feasible split points in the RAN architecture. In general, when more functions are located at the cell site the speed and latency demands placed on the transport network are reduced, but the gains that can be provided by baseband pooling are also reduced. This means that the optimal split point in the architecture depends on the specific network and transport conditions in