# Multi-RAT Orchestration Method for Heterogeneous Wireless Networks
## 2 State-of-the-Art
Thus, in the case of bottlenecks and lack of free radio resources, it may be impossible to serve users, especially those who do not have an appropriate profile determining a higher priority in access to resources or are not within the coverage of LTE networks. As part of the work on the LTE standard, 3 GPP has developed the possibility of cooperation with WLAN networks by integrating them directly into the EPC backbone network (so-called non-3 GPP Access). At this level, the EPS allows the non-3 GPP network to be connected to the EPC. This applies to WLAN networks, WiMAX, and fixed cable networks. Non-3 GPP is divided into trusted and untrusted access. The operator defines the group to which the given network belongs. Trusted non-3 GPP networks can obtain a direct connection to the EPC. In contrast, untrusted non-3 GPP networks can connect to the EPC through a dedicated node called ePDG (Evolved Packet Data Gateway), whose role is to provide security mechanisms (Figure 2). As part of access to the LTE network through non-3 GPP networks, a mechanism related to the so-called IP Mobility is implemented [25; 26]. Among others, owing to the IFOM solution (Mobility with IP address preservation for selected IP flows), the user terminal supporting this functionality has the ability to route different IP routes to the same PDN (through different access networks). It should be emphasized that packet route choices cannot be made in remote data centers due to delays that would be unacceptable for the adopted solutions. These solutions are not intended for choosing a radio interface that could completely replace the cellular network (here LTE), which is treated as the basic RAT from the user service point of view. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Radio Interface** & **Solution** & **3 GPP Release** & **Standalone Operations** \\ \hline
4G/LTE & LAA & Rel-13 & No \\
4G/LTE & eLAA & Rel-14 & No \\
4G/LTE & feLAA & Rel-15 & No \\
4G/LTE & MulteFire & - & Yes \\
5G/NR & NR-U & Rel-16 & Yes \\ \hline \hline \end{tabular}
\end{table} 
Table 2: List of 3 GPP products and functional solutions enabling data transmission in unlicensed bands. In 5G/NR networks, cooperation with non-3 GPP networks is also provided and is supported by the non-3 GPP Interworking Function (N3 IWF) component, where it acts as a gateway to the 5G network. It is worth emphasizing that the use and integration of a specific network (e.g., WLAN) as a non-3 GPP network requires cooperation with the operator. Thus, in this study, the management of access to the network from the E2E level is considered where the decision-making processes are taken both beyond the access network and the backbone. Orchestration at a higher level (over 3 GPP networks) allows, in particular, management of traffic in places where the 3 GPP network is unavailable (especially in case of lack of coverage) or its parameters do not allow implementation of a specific KPI defined by the user for a given end-to-end links (such as energy efficiency). Such orchestration requires the use of specific policy rules, which may relate generally to both technical parameters (QoS, KPI) and business indicators (link cost, selection of specific equipment suppliers), or others (selection of licensed/unlicensed bandwidth, energy consumption on a given path, and others). The possibility of using multiple RAT networks allows for a broader definition of orchestration parameters and is not limited to only qualitative criteria. Decision rules can be freely defined and changed at the programming level, without the need to violate solutions of radio interfaces. The scope and type of networks will depend on the manager ordering the multi-RAT networks. According to the development of new telecommunication standards and introduction of new services, there is an expectation and strong pressure to improve mobile terminal power consumption.