# Device Management and Data Transport in IoT Networks Based on Visible Light Communication
## 3 Proposed VLC-Based IoT Scheme  
### Network Reference Model  
For VLC-based IoT networks, we consider the following four types of network nodes: Platform Server (PS), Aggregation Agent (AA), VLC Transmitter (VT), and VLC Receiver (VR). There are two possible communication scenarios between VT and VR, as shown in Figure 1. Figure 1 depicts bi-directional VLC between VT and VR, in which both uplink and downlink VLC transmissions are allowed. On the other hand, Figure 1 shows uni-directional VLC from VT to VR, in which only downlink VLC transmission is allowed from VT to VR, and the uplink or backward transmission will be made between VR and AA by using another network link, such as WLAN or WPAN.  
Figure 1: VLC communication scenarios: (**a**) bi-directional VLC; (**b**) uni-directional VLC.  
It is noted that most real-world VLC deployments follow the uni-directional model displayed in Figure 1b, even though the IEEE 802.15.7 specification defines both bi-directional and uni-directional models. This is because the implementation of bi-directional VLC requires multiple light sources or more complex MAC algorithms. Based on this observation, this paper proposes the VLC-based IoT scheme based on the uni-directional VLC model. The bi-directional VLC model will be considered for further study.  
Figure 2 shows the network reference model for the VLC-based IoT scheme, in which the network entities are classified as Platform Server (PS), Aggregation Agent (AA), VLC Transmitter (VT), and VLC Receiver (VR). Each network entity provides the following functionality:  
* Platform Server (PS) PS performs overall management for all devices, including AAs, VTs, and VRs, in the VLC-based IoT network through the operations of device initialization, monitoring, and VR handover. PS also controls location-specific VLC data (from VT to VR) and service-specific data (between AA and VR) by using the data transport operation. PS is connected to the Internet.
* Aggregation Agent (AA) AA manages VT and VR devices locally. It keeps and updates the VT-VR mapping information for its attached VT through the device initialization, monitoring, and VR handover operations. That is, AA can realize the list of VRs that is connected to a specific VT. AA also supports the VR service channel with VR, in which AA exchanges service data with VR. AA is also used to relay location-specific VLC data between PS and VT, and service-specific data between VR and PS.
* VLC Transmitter (VT) VT controls the LED light. When VT is connected and registered to AA, it transmits location-specific data with VLC frames toward VRs.
* VLC Receiver (VR) VR is a user or sensor device which acts as a VLC receiver. When VR receives VLC frames with the location-specific data from VT, it will begin the registration with AA. If VR is connected to AA, it may request service data from AA, based on the context of the location-specific data.  
Figure 2: Network reference model for VLC-based IoT.  
In Figure 2, there are four types of network links. The green line linking AA and PS could possibly be Ethernet. The blue line between AA and PS could be Ethernet or Wireless LAN (WLAN) [29]. The yellow triangle illustrates the VLC frames transmitted by LED light. The red links indicate the service channel between AA and VR. This service channel could be WLAN or WPAN, such as ZigBee, BLE, Z-Wave, etc. It is noted in the proposed scheme that this service channel is employed to provide the uplink or backward communication from VR to AA or PS, as discussed with respect to Figure 1b.