Tutorial on communication between access networks and the 5G core

Fifth-generation (5G) networks enable a variety of use cases that require differentiated connectivity, e.g., Ultra-Reliable and Low-Latency Communications (URLLC), enhanced Mobile Broadband (eMBB), massive Machine Type Communication (mMTC). To explore the full potential these cases, it is mandatory to understand communication along with 5G network segments architecture components. User Equipment (UE), Radio Access Network (RAN), Core (5GC) are main components support new concepts paradigms. 3rd Generation Partnership Project has recently published Release 16, including protocols used communicate between RANs 5GC, i.e., Non-Access Stratum (NAS) NG Application Protocol (NGAP). The goal this work present comprehensive tutorial about NAS NGAP specifications using didactic practical approach. describes protocol stacks aspects functionality in networks, such as authentication identification procedures, data session establishment, resource allocation. Moreover, we review message flows related UE Next Node B (gNodeB) registration. illustrate presented tutorial, developed my5G Tester: 5GC tester implements for evaluating three open-source projects black-box testing methodology.