# Toward a Detailed Evaluation of Wireless Industrial Data Distribution Approaches +
## 3 Methods for Industrial Data Distribution  
In this section, we design four methods targeting data distribution for wireless industrial networks. We first present the network model we consider, then the technological and methodological building blocks that we use and finally the centralized and decentralized methods that we design.  
We consider networks of industrial devices which consist of sensor motes and actuators and are operating at the physical layer in the 2.4 GHz ISM band using IEEE 802.15.4 radios; this choice is in accordance with the operating conditions of WirelessHART, thus guaranteeing fair comparison among the analyzed methods. In network configurations of such type, a central network controller (CNC) maintains centralized network knowledge. This is usual in industrial applications, in which the locations of the nodes are known, traffic flows are deterministic and communication patterns are established a priori. We assume that the CNC knows all the shortest paths in the network. This is in accordance with the functionalities in charge to the 6 LBRs (6 LoWPAN area border routers) in the 6 TiSCH architecture for industrial networks.  
Sensor nodes perform monitoring tasks (producers), and in some cases, their sensor data are needed either by other sensor nodes, which could need additional data to complement their own local measurement, or by actuator nodes, which use the sensor data so as to perform an actuation (consumers). When needed, a consumer can ask for data of interest from a sensor node using the primitives defined by the specific industrial application; application messages are forwarded to their destinations by leveraging the service provided by the underlying routing protocol. As said, the CNC is in charge of the control plan managing the data distribution process. However, the actual data distribution may be decentralized and cooperative by delegating to identified nodes in the network (_proxies_) the data caching. Proxy nodes are able to store data that can be accessed in a timely manner from the consumer nodes of the network.  
We assume that the data generation and access processes are not synchronized. Specifically, we assume that data consumers request data at an unspecified point in time after data have been generated by data producers. This demarcated model of data exchanges can be formulated as a publish-subscribe (pub/sub) model [29]. In a pub/sub model, a consumer  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Paper** & **Methodological** & **Simulative** & **Deployment** \\ \hline Current & ✓ & ✓ & ✓ \\ [19] & ✓ & - & - \\ [20] & ✓ & - & - \\ [21] & ✓ & - & - \\ [22] & - & ✓ & - \\ [23] & - & ✓ & - \\ [24] & - & ✓ & - \\ [25] & - & - & ✓ \\ [26] & - & - & ✓ \\ [27] & - & - & ✓ \\ [28] & - & - & ✓ \\ \hline \hline \end{tabular}
\end{table}
Table 1: Comparison of the reported related works.  
subscribes to data, i.e., denotes interest for it to the corresponding proxy, and the relevant producer publishes advertisements to this proxy. The pub/sub process is regulated at the CNC, which maintains knowledge on the sets of producers, consumers and requests. Based on this, the CNC can find an appropriate set of proxies based on the algorithm we present next. Inside the network, the proxies are responsible for matching subscriptions with publications, i.e., they provide a rendezvous function for storing the available data according to the corresponding subscriptions. The producers do not hold references to the consumers, neither do they know how many consumers are receiving their generated data.