## 4 Proposed Architectural Approach
### Network Telemetry  
Network telemetry (NT) is real-time data collection in which devices push data to a centralized location. Telemetry metrics are generated from enterprise resources, such as switches, routers, wireless infrastructure and IoT systems, and used by business and technology applications to monitor trends and help IT respond to threats or react to changing network conditions [39]. As depicted in Figure 5, the NT framework provides analytics information for different analytic events to NF consumers, by subscribing to (1) one-time notification, (2) periodic notification, or (3) notification when an event is detected, either in the form of statistical information concerning past events, or as predictive information. In our proposed approach, NT will be able to gather related data from all defined architectural layers. In this context, two significant NT components are determined, namely the NWDAF and the centralized management data analytics function (C-MDAF), where the first one is a well-specified component of the 5G CN according to 3 GPP standards and ETSI technical documents.  
The NWDAF is a new feature of 5G networks, which enables the network operators to either implement their own ML-based data analytics methodologies or integrate third-party solutions to their networks. NWDAF, which is defined in 3 GPP TS 29.520 [40], incorporates standard interfaces from the service-based architecture to collect data by subscription or request data from other network functions and similar procedures. The NWDAF in the 5 GC plays a key role as a functional entity that collects KPIs and other information about different network domains and uses them to provide analytics-based statistics and predictive insights to 5 GC network functions, for example to the policy control function (PCF). Advanced ML algorithms can utilize the information collected by the NWDAF for tasks such as mobility prediction and optimization, anomaly detection, predictive QoS and data correlation [41].  
In order to support a wide variety of services and requirements and increase the flexibility, a centralized telemetry node should take advantage of management data analytics services (MDAS) towards improving the network-wide performance and efficiency [42]. These services are provided by the management data analytics function (MDAF). In principle, an MDAS offers data analytics of diverse network parameters including resource management information for a specific NF (e.g., NF's load, resource usage status of an NF, etc.). Since the NWDAF can offer telemetry capabilities only on the CN side, the inclusion of an additional MDAF entity in the proposed architecture could extend the NT functionality towards the RAN and TN sides, as well as inter-connect the RAN, TN, and CN-oriented telemetry.  
Towards this direction, C-MDAF is provisioned to host all the centralized telemetry capabilities and to be located at the MOA Layer (Figure 5). A particular NF may subscribe to the C-MDAF as a consumer in order to collect or provide data for forecasting or resource usage information purposes. Moreover, the data analysis can also identify corrective actions in the network, e.g., scaling of resources, load balancing of traffic, etc.