## 5 Proposed VLC-IoT Network Architecture  
Obviously, the numerous promising features of VLC mentioned above engender VLC as an attractive solution where connectivity and quality of service (QoS) for massive IoT devices are challenges. Therefore, VLC needs to be integrated with IoT in such a manner that it supports massive connectivity and meets the stringent QoS requirements of IoT devices. In this section, we propose a network architecture prototype for the deployment of a prospective VLC-IoT network. Figure 1 shows our proposed VLC-IoT architecture.  
The proposed architecture comprises a VLC-aided central network, e.g., VLC-aided smart home, VLC-aided smart transportation, etc., a set of sensors and actuators and APs that are capable of communicating with VLC-IoT devices with different communication technologies [16; 38]. Essentially, each technology and network is a sub-network of the architecture. The central network, e.g., the VLC-aided smart home consists of a number of VLC APs fitted to the room ceiling or street/traffic lights in VLC-aided transportation [39]. Each VLC APs has LED lamps for lighting which also supports communication for IoT devices. The sensors and actuators network consist of sensors that collect and transmit data as well as actuators that perform specific IoT-related functions [40]. A ZigBee coordinator manages and controls the interaction and communication between the sensor and actuators that use the ZigBee communication protocol, while a VLC gateway coordinates the communication of nodes in the sensors and actuators network that use the VLC protocol [41]. The communication between the central networks and the sensor and actuator network is executed using LoRaWan/LTE-M to permit long-distance communication between the sensors and the internet network. The architecture deploys a frame format that permits node discovery, identification, and routing so that each node can effectively communicate with other nodes in the architecture. The frame format is capable of redirecting data and controlling messages between the different subnetworks and is compatible with VLC technology. When a frame arrives at an AP, the AP reroutes it within a subnetwork or outside the subnetwork using unique node identifiers and a MAC which directs the frame to the destination IP address [19; 38]. The frame translation, re-routing, node identification, and communication functionalities which guarantee interoperability between the different technologies are realized by a layered model. The protocol stack executed in the model allows the VLC-IoT nodes to translate frames arriving from different technologies and to redirect them to the IP address inside the cell or outside the cell. The resultant frame is suitable for communication with any device on the network regardless of their subnetwork or protocol. As presented in Figure 2, the protocol stack is driven using a cross-layer  
Figure 1: Proposed VLC-IoT network architecture.  
optimizer. Moreover, the protocol stack is implemented in a software-defined fashion to enable intelligent and fast adaptability to achieve optimized performance between protocol layers. The front-end hardware implemented in the VLC-aided IoT network are LEDs as transmitters and photodiodes, optical cameras as receivers, and LoRa gateways.