 xRAN (which later became O-RAN Alliance). The fronthaul traffic flow procedures and the requirements on the fronthaul transport network to satisfy timing and latency constraints of such deploy- ment are also discussed in this section. 4.5.1 Key Ideas The benefits of putting more RAN processing resources at a central location were estab- lished long time ago. The centralized RAN has the benefits of performances gains due to centralized scheduling and RRM, and resource pooling. Furthermore, it allows the lever- aging of commercial off-the-shelf (CoTS) hardware and virtualization. However, these benefits are only limited to functions centralized, hence the desire to centralize as much functionality as possible. The desire to move more RAN functions into a centralized processing unit requires a gNB functional split point further down the physical layer, resulting in a physical layer implementation which processes the radio signals that is split across two network nodes. The network nodes in the LLS gNB architecture are connected by the fronthaul inter- face, which has to transmit a large quantity of the radio data in a short period of time, imposing strict requirements on the transport network bandwidth and latency. Further- more, physical layer processing requires stringent timing in order to guarantee timely radio signal transmission timing over the air. All of these factors need to be considered when designing the LLS NG-RAN. 3GPP studied (3GPP TR 38.801) several LLS options. In option 8, which separates the RF function from the DU, the fronthaul transport carries the time-domain I/Q data streams. In option 7, which puts some physical layer functions in the RU and leaves the rest of the 4 NG-RAN Architecture physical layer functions in the DU, the fronthaul carries the frequency-domain I/Q data streams. Option 7 can be further divided into several suboptions, based on the level of physical layer functions residing in the RU. LLS can only be deployed if the fronthaul transport network satisfies its bandwidth, late