## 3 Architectural Approaches  
In this section, the most important architectural approaches in the context of 6G networks are described. To this end, in [55], the authors introduce the concept of organic 6G network architecture, the main core of which relies on the execution of all architectural protocols as web-based services. This approach tries to extend the SBA that was introduced in the 5G era as an attempt to decouple network deployment from hardware-specific and constrained devices. The organic concept moves a step forward by allowing each functionality to be executed as a microservice. Therefore, the concept of infrastructure-free implementation can be supported. In parallel, each service requests a specific amount of network infrastructure; hence, network size depends on the actual requirements of the application. In [56], a novel architectural approach is presented that can support threat prediction and mitigation, as well as privacy protection, in 6G networks. To this end, one of the key components of the presented approach is the distributed trustable engine (DTE), which collects real-world network data and trains ML models in FL mode. This architectural approach supports DTs as well, since the DTE can also work with the emulated context. This training has a dual goal: (a) to identify abnormal data patterns and (b) to identify potential security attacks. Afterwards, the intent-based interface (IBI) creates appropriate intents that are translated to specific network reconfigurations. Each such intent can be either predictive (i.e., the appropriate actions to avoid an attack) or mitigative (i.e., the set of appropriate actions for the network to recover from an attack). Hence, this approach can be highly applicable in zero-day attacks: if an actual attack takes place, then the IBI can create the appropriate intents for network restoration. In the same context, if  
Figure 8: A high-level 6G architectural approach. a similar attack is identified in another network topology, then mitigation actions can be deployed in the considered topology either with emulated content from the DT to the DTE, or via transfer learning, which integrates additive knowledge from the specific attack [57]. In [58], various security aspects are analyzed in the context of 6G networks. This analysis includes both the physical and the network layer. In the physical layer, for example, potential attacks involve eavesdropping, jamming, pilot contamination attacks, and spoofing. In the same context, specific countermeasures are also proposed for each type of attack. The use of IRSs, for example, which reflect the signal in unpredicted ways, can be beneficial for attack mitigation, since the attacker will be unable to know the exact direction of the incoming signal. Moving forward, the use of network slices can partially mitigate network attacks, since inter-slice information is not transmitted. Hence, potential attacks can be limited to only a single slice. In [59], the network-slicing concept is introduced in 6G networks. To this end, a detailed approach is provided that formulates the optimization problem by taking into account various performance metrics, such as resource allocation, service provisioning, and performance optimization. In the same context, the process of slice allocation first considers all resource requests from the various 6G layers. Afterwards, the optimization problem leads to optimum slice allocation. In [60], the concept of CF networks is introduced. As previously mentioned, various APs are placed within the wireless topology and MSs are connected to each AP based on their signal strength and channel quality. In this work, the coexistence of CF approaches with current network architectures is examined, in particular, the criteria for either centralized or distributed signal processing. In [61], various key enabling technologies in the context of 6G networks are introduced and analyzed.