## 5 Discussion  
There is no out of the box solutions to connect an SAP MES with a ROS-based AIV that the authors are aware of. Different organizations and consortiums are working to come up with a solution. Recently, ROS-Industrial had the opportunity to collaborate with Microsoft, BMW, and Open Robotics on an automation solution to integrate SAP with fleet management and navigation functionality [42], as BMW required a way to connect their robots to an open-source platform, allowing a heterogeneous fleet of robots to work together in perfect harmony with the human workers on the assembly line. The main objective of this work was to provide a possible solution to integrate a ROS-built low-cost AIVs with a MES. The literature review shows that there is published work available on MES related research and robotic automation but to the best of the authors' knowledge, no published work provides a detailed solution on how to integrate a low-cost AIVs with an MES. As mentioned in Section 1, there are some AIVs [30; 31] commercially available, which offer communication with MES but the manufacturers of these AIVs offer industrial solutions at a very high-cost and under  
Figure 19: Testing setup. Here, the coordinates of single pickup location are used for two pickup locations and similarly scheduler is tested for three drop-off locations by using coordinates of single drop-off location. Figure 20: Scheduler interface  
license. In addition, the greatest benefit to a company to building customized solutions using low-cost, self-build AIVs is the ownership of products and systems and potential sales to partner companies. The proposed integration solution here used ROS-built AIVs because ROS is open source and does not have any license requirements. The scheduler is developed using LabVIEW software, and as mentioned earlier, the main reason to select LabVIEW as a middleware platform is that it has support for both webservices and the ROS platform. The LabVIEW platform is not new for industries, it is used for many applications like building maintenance, testing, monitoring, and automation applications. LabVIEW is used in this work because it is an attractive platform for users with a non-programming background and comparatively quick programming is possible using LabVIEW. Other software tools can require programming abilities or have limitations with regards to the integration of the AIV and MES. For example, Node-RED has support for webservices but ROS support is limited [43]. In addition, LabVIEW has support for the widely used industrial protocols like OPC UA (Open Platform Communications Unified Architecture), MQTT (Message Queue Telemetry Transport), and AMQP (Advanced Message Queuing Protocol) [44; 45; 46]. A brief discussion about these industrial protocols is given below. Industrial protocols are real-time communication protocols, developed to interconnect the systems, interfaces, and instruments. The main goal of industrial protocols is to apply one communication technology across all levels of factory automation. The OPC UA [47; 48] is currently the most widely used industrial protocol. This protocol supports high scalability, availability, and implements Internet capabilities, as well as secure cross-platform data exchange. The new features of OPC enable a model in which a server sends its data to the network (publish) and every client can receive this data (subscribe). The MQTT [49] is another industrial protocol that was created to collect data from many devices and then transport that data to the IT infrastructure. It is lightweight and, therefore, ideal for remote monitoring. The publisher/subscriber model of MQTT decouples the client that sends a message (publisher) from the client or clients that receive the messages (subscribers). One more example of the industrial protocol is AMQP [50], which creates interoperability between clients and brokers.