# Effects of Transport Network Slicing on 5G Applications
## 2 The NCTU Testbed  
At NCTU, we have developed a 5G testbed based on P4 switches and free5 GCTM [16], an open-source solution for 5G core networks. Figure 2 shows the architecture of the NCTU testbed, where the UE (Figure 2 (1)) accesses the IoTtalk services (Figure 2 (2)) through the RAN (Figure 2 (3)), and the UPF implemented in a Programming Protocol-Independent Packet Processors (P4) switch (Figure 2 (4)). This implementation decouples the UPF into a PFCP agent on the Software-Defined Network (SDN) controller (Figure 2 (5)) as the UPF control plane and a UPF data plane in the P4 switch. Besides, a P4-based transport network (Figure 2 (6)) with one or more P4 switches connects the RAN to the P4 UPF and other free5 GC network functions (Figure 2 (7)). The P4 transport network is where we excise the network slicing on various applications.  
The P4 switches employed in our testbed include the Edgecore Wedge 100 BF-65X (65 \(\times\) 100 Gb/s), Edgecore Wedge 100 BF-32X (32 \(\times\) 100 Gb/s), Inventec D5264 (64 \(\times\) 100 Gb/s), and Inventec D10056 (48 \(\times\) 25 Gb/s + 8 \(\times\) 100 Gb/s), and are controlled by the SDN controller. Aside from the control and user planes, 3 GPP also defines the network management architecture for the 5G system [17]. The 3 GPP Management System can interact with the ETSI Network Function Virtualization MANO (NFV-MANO) specification for E2E  
Figure 2: An SDN-based 5G architecture using P4 switches on the National Chiao Tung University (NCTU) campus. All IoT devices and UEs (**1**) access an IoTtalk server (**2**) in the DN through either the RAN (**3**) or the Non-3 GPP Inter-Working Function (N3 IWF) networks (**9**). All application traffic is forwarded through a P4-enabled transport network (**6**) managed by an SDN controller (**5**) as well as a P4 UPF (**4**) managed by the 5G control plane (**7**). A 3 GPP management system (**8**) is a management plane that carries out an E2E network slice through (**3**), (**5**), and (**7**).  
network slicing; that is, the 3 GPP Management System and ETSI NFV-MANO (Figure 2 (8)) manages resources through the RAN, the SDN controller, and the 5G control plane.  
In this testbed, a UE communicates with the AMF through the path (1)-(3)-(6)-(7). The AMF contacts the NSSF to identify the network slice of the UE and selects an active SMF to delegate the management of the UE's PDU session to said SMF. The SMF then establishes a PDU session on an appropriate UPF. After completing this establishment, the UE can access network services through the given UPF. In our testbed, the SMF in the control plane controls the UPF in the P4 switch through the PFCP agent in the SDN controller, which is responsible for issuing the corresponding SDN instructions to the P4 UPF; the path for this process is (7)-(5)-(4).  
All application traffic is directed to the NCTU testbed and serviced by corresponding network slices managed by an NFV Orchestrator (NFVO) in the 3 GPP Management System. We would also like to point out that most applications are directly connected to the NCTU testbed through the N3 IWF networks (Figure 2 (9)) without passing through the expensive 5G new radio. Thus, this article describes the 5G applications that take advantage of SDN, NFV, and network slicing features in the transport and the core networks, but not the 5G new radio.