# Network Slicing for mMTC and URLLC Using Software-Defined Networking with P4 Switches
## 2 Related Works  
Most studies on IoT in modern communication networks have aimed to reduce the high collision rate of the random access channel (RACH) competition mechanism in 5G. If numerous mMTC devices appear in a radio access network (RAN), the number of mMTC devices that can successfully connect is drastically reduced, reducing the mMTC connection density. Studies on this phenomenon can be broadly divided into those on LTE-machine (LTE-M) [24; 25] and narrowband IoT (NB-IoT) communications [26; 27; 28]. These two technologies use different cell coverage areas and reserve different numbers of resource blocks (RBs) during a frame period. By adopting simpler coding techniques or lower data transmission rates for dedicated RBs, the mMTC connection density can be increased. Table 1 presents a comparison of the LTE-M and NB-IoT parameters based on 3 GPP-Release 13 [29]. Several studies have applied artificial intelligence algorithms to RACH collision detection [30; 31; 32; 33]; these algorithms can dynamically adjust the time that each mMTC device accesses the RAN to reduce the probability of access collisions if numerous mMTC devices simultaneously attempt to connect. Key 5G network services include not only mMTC, but also URLLC and must support their heterogeneous requirements. Relevant research on supporting both mMTC and URLLC in 5G networks typically covers one of the following groups of topics:  
1. Bandwidth resource allocation, differentiating access times, or RAN frequency reuse. 2. Dividing the entire network into multiple virtual E2E networks (i.e., network slices) by using virtualization technology. Network slices are independent of each other in their equipment, access, transport, and core networks. Many authors have proposed solutions for 5G networks with numerous coexisting IoT devices and URLLC services [3; 34; 35; 36; 37; 38; 39; 40; 41; 42]. The authors of [3; 39; 40; 41; 42] proposed mechanisms for bandwidth resource allocation, differentiation of access time, or frequency reuse in the RAN of 5G networks to enable the provision of multiple service types by reducing the probability of access collisions and increasing the efficiency of bandwidth use. [PERSON] et al. [3] indicated that even a network dominated by IoT services may require handling short-term emergencies, such as those at large-scale disaster sites or the wireless monitoring of factory automation, in which quality requirements are similar to those of URLLC. Therefore, 5G network designs must be effective for both mMTC and URLLC services. Fifth-generation NS can simultaneously meet the heterogeneous quality requirements of mMTC and URLLC [34; 35; 36; 37; 38; 39; 40; 41; 42; 43; 44; 45; 46; 47; 48; 49; 50; 51;  
mentioned in Section 1, on an SDN with traditional switches, the state information of all packets cannot be maintained in the data plane and relies only on the actions of the controller in the control plane, which may result in processing delays and a control channel bottleneck between the controller and switches. The solution to this problem is to use higher-level interface standards, such as P4 [19], between the controller and switches. [PERSON] et al. [43] proposed an enhanced SDN switch with forwarding actions specified by the P4 language. Its SDN functions were enabled by using the P4 runtime as the control plane protocol to specify the forwarding rules in the programmable data plane. The enhanced switch could autonomously define forwarding rules by using P4 registers, thereby preventing SDN controller overload. The authors of [44] presented a programmable data transmission path design between user equipment-RAN and user plane function for industrial 5G networks. They also discussed methods of supporting URLLC services with lower latency in 5G networks by using P4 switches as required in industrial applications. [PERSON] et al. [45] illustrated the potential of the P4 language, aiming to show its innovative functionalities at the data plane level, and provided five use cases.