# Application-Aware Network Traffic Management in MEC-Integrated Industrial Environments
## 3 MEC-Integrated Industrial Environments  
Nowadays, manufacturing companies are logically organized on three primary levels: shop floor, plant, and enterprise [36]. The shop floor level is mainly focused on industrial automation. As depicted in Figure 1, the primary components of the shop floor are industrial machines, Programmable Logic Controllers (PLCs), Human-Machine Interfaces (HMIs), IIoT devices, and AGVs. Industrial machines tend to have extremely long lifetimes (in the order of decades) and may implement different (proprietary) protocols. In addition, software upgrades may not always be possible, because manufacturers usually forbid software upgrades for safety reasons, or industrial machines may not support them at all. Instead, IIoT devices are characterized by a substantially shorter lifetime and usually communicate via well-known protocols. Then, PLCs are tailor-made devices for controlling manufacturing processes while coping with the harsh conditions affecting industrial environments, such as temperature surges, vibrations, and electrical noise. Human operators interact with and receive feedback from industrial machines through HMIs, specifically designed for improving operator decision making. In addition, the shop floor has been recently enriched by the deployment of AGVs, automating the process of moving products among different parts of the industrial environment. The plant level regards the management of manufacturing processes. The critical component is the Manufacturing Execution System (MES). In particular, the MES receives instructions from operators about how industrial machines should behave, and then it transmits such instructions downward, i.e., toward the shop floor. As the requested manufacturing process goes into production, the MES matches the instructions provided by the operators against the actual actions taken by industrial machines. If the current actions do not match the desired actions, the MES applies corrective measures. The enterprise level is about making decisions on how to run business operations. In this regard, decision makers rely on the Enterprise Resource Planning (ERP). The ERP collects information from the underlying business assets, such as supply chains, cash flows, customer orders, and production processes. Then, it processes such information by using business analytics to provide decision makers with an enterprise-wide picture of what is going on. The Purdue model [37] is arguably the most common network implementation of such a logical structure. A pillar of the Purdue model is the concept of network segmentation. In particular, the Purdue model recommends a hierarchical approach that splits the industrial network into five layers. The lower three layers concern OT, whereas the upper two concern IT. The shop floor components crafting goods belong to layer 0/1. This layer relies on a time-sensitive network connecting industrial machines and PLCs. Then, layer 2 hosts devices that control the crafting processes (e.g., HMIs), whereas layer 3 includes those components that manage the manufacturing process as a whole (e.g., the MES). Finally, layers 4 and 5 consist of more IT-oriented functionality and facilities, such as Web servers, email servers, databases, and the ERP system, to name a few. From a networking perspective, each layer of the Purdue model is supposed to be supported with differentiated performance levels. As a rule of thumb, the lower, the better. For example, because layer 0/1 must meet safety-critical requirements, the network is expected to provide high reliability and low latency (e.g., within 10 ms). However, layer \(0/1\) does not typically provide computing resources as abundantly as the upper layers. In this regard, layer 2 tends to provide worse network performance (e.g., within 25 ms) than layer \(0/1\), but it also potentially provides more computing resources and less stringent security requirements.