 view, OAI contains both RAN (E-UTRAN) and core (EPC), which can be deployed together in one platform or on separate network nodes. Further- more, the OAI project also has an open source UE implementation. The OAI RAN imple- ments the PHY and all the air interface protocol stack layers (as described in Chapter 3); however, only the essential features required to build a functioning network have been implemented SO far. Furthermore, the OAI RAN implements the X2 and S1 interface, once again with a limited set of functionalities - for example, X2 handovers are supported, but scheduling and resource coordination via X2 are not. From the internal RAN architecture standpoint, the OAI RAN implements a number of split options (see Chapter 4 for details), as shown in Figure 6.3.2. The splits shown in Figure 6.3.2 do not follow exactly the specifications and standardized architectures described in Chapter 4, but are rather "inspired" by these: The IF1 interface is conceptually similar to the 3GPP F1 (3GPP TS 38.470) interface (described in Section 4.2). Note that the 3GPP F1 interface currently only supports 5G, whereas OAI IF1 supports only LTE. In particular, this means that there are major dif- ferences between 3GPP F1 and OAI IF1. That being said, once 3GPP has specified the equivalent of F1 for LTE (referred to as W1), it is likely that OAI IF1 implementation will align to that W1 spec. (3GPP TS 37.470). Moreover, when OAI finally supports 5G, it is likely that OAI 5G IF1 will follow the relevant 3GPP specification. IF2 is similar to the Small Cell Forum FAPI interface (described in Section 4.6). IF4.5 is similar to the O-RAN low-level interface (described in Section 4.5). IF5 is similar to Common Public Radio Interface (CPRI). 6.3 Open Source IF4.5 LTE-L1 MAC-RLC MODEM LTE/NR/NB nFAPI LTE-L1 MAC-RLC MODEM Radio Cloud Center (RCC) Radio Access Unit (RAU) Remote Radio Unit (RRU) data (user/control plane) configuration Figure 6.3.2 OAI RAN architecture. As mentioned above, one should not assume that OAI interfaces IF1,