# SRv6-Based Edge Service Continuity in 5G Mobile Networks +
## 4 Architecture and Procedures for MEC-Based Mobile Services  
In this section, we describe a converged 5G and MEC architecture that combines elements from both domains. Our focus is on how these components interact and enable efficient service delivery and their seamless migration at the network edge. We consider a modified version of the 5G MEC architecture proposed in [9]. Our architecture is shown in Figure 3. Using Figure 3 as a reference, the Radio Access Network (RAN) serves as the bridge between user equipments (UEs) and the cellular network. It encompasses base stations (gNBs in 5G terminology) and handles radio-resource management, modulation, and demodulation. The 5 GC forms the central part of the 5G system, providing connectivity between the RAN and other data networks. The data plane (or user plane in 5G terminology) is composed of one or more User Plane Functions (UPFs) that process and forward user data to/from external data networks. UPFs can be deployed as part of the external data networks, such as an MEC deployment, although remaining logically a component of the 5 GC. In current 5 GC architectures, the communication between the RAN and the UPF, and among UPFs, is handled by the GPRS Tunneling Protocol User Plane (GTP-U). However, several studies and standardization efforts from both 3 GPP and IETF are proposing SRv6 for substituting GTP-U toward a full-IP 5 GC [13; 14]. We follow this approach, and we consider the user plane to be composed of SRv6-capable UPFs. We note that additional SRv6 nodes can be deployed between UPFs, e.g., to embed virtualized network functions (VNFs) or for traffic engineering purposes [13]. In the following, we will refer to both these nodes and UPFs as SRv6 nodes. In Section 4.2, we will present the procedures related to configuring SRv6 nodes for forwarding IP packets through the data plane. The 5 GC control plane is composed of several functions controlling and configuring both the core and access network aspects. Each function offers one or more services to other functions in the networking through a service bus, following a so-called Service-Based Architecture (SBA). From the perspective of this work, the functions of interest are the Access and Mobility Management Function (AMF), Session Management Function (SMF), and the Network Exposure Function (NEF). The AMF handles UE registration and session management and is responsible for user mobility management, authentication, and security. The SMF controls session establishment, modification, and termination, and is responsible for routing data between UEs and external networks. In the considered architecture, the AMF and SMF will be responsible for configuration, respectively, in the gNBs and in SRv6 nodes. As far as the IP packets forwarding is concerned, we will assume the SMF to configure it through a dedicated SDN controller. In more detail, as reported in [34], the SMF sees the SDN controller as a UPF. Communication between the SDN controller and the SMF is enabled via the N4 interface. The SDN controller, instead, configures the forwarding rules on SRv6 nodes. The utilization of an SDN controller allows us to decouple the SMF and the network devices, creating a hybrid SDN network wherein different protocols can be employed for device configuration [35]. Following this approach, the SMF is not required to interact with devices directly; instead, it only needs to communicate with the SDN controllers using a standard 3 GPP interface. Finally, the NEF provides APIs for exposing network capabilities to external systems, e.g., letting them request network reconfiguration to the AMF or SMF. Figure 3: Converged 5G and MEC reference architecture. In a typical deployment, both the 5G control plane components and the SDN controller should be replicated so that they do not constitute a single point of failure. They must provide high availability and they must ensure consistency. Exploiting SDN controllers for routing rules configuration also facilitates the adaptability of the solution for hybrid networks.