**Abstract**

In this chapter, the main methods of communication among multi-robot systems involved in Machine-to-Machine (M2M) applications, especially with regard the communication, reliability, stability and security among these robots, presenting various concepts through papers already published. A comparative study was carried out between two communication protocols applied in M2M technologies, the Queue Telemetry Transport (MQTT) developed by IBM along with Eurotech and the Constrained Application Protocol (CoAP). A study and survey of the characteristics of each of the protocols was carried out, as well as the method of operation of each of them and how both can be used in applications involving multiple robots. It was concluded that both protocols are considered ideal for use in in applications involving multi-robot systems. However, although the two protocols have been designed for application in environments with limited communication, the MQTT exchange protocol has advantages over CoAP, as a lower ovehead between message exchanges.

**Keywords:** Machine-to-Machine, protocol, multi-robot system

#### **1. Introduction**

The industry, in the last century, has undergone changes in the way it operates, generating innovation and profound social and economic changes. According to [1], is the beginning of a revolution called Industry 4.0. This industrial revolution is based on several concepts, among them, the Cyber-Physical System, Internet of Things (IoT), big data analytics, Machine-toMachine (M2M) and cloud computing. All of these concepts aim to meet the requirements of an advanced manufacturing system, promoting the integration of an entire supply chain.

The authors in [2], Industry 4.0 creates what has been called the smart factory. This factory has a modular structure in which cyber-physical systems monitor physical processes, creating a virtual copy of the physical world, making decentralized decisions using the IoT that has communication with each other and with humans in real time. These smart factories aim to solve several challenges found in large industrial systems, due not only to the increase in the complexity of processes and products, but also to the increase in the varieties of these products, which must be placed on the market due to the reduced life cycle. Thus, there is a need to make production processes more flexible, characterized according to [3] in production systems with distributed units, composed of a conglomerate of autonomous units, which operate in cooperation in an integrated manner. Such units can be industrial automation machines, manipulating robots, mobile robots or microprocessed remote units.

**2.1 M2M architecture**

described as follows:

• In the domain of devices:

*Interaction Protocols for Multi-Robot Systems in Industry 4.0*

*DOI: http://dx.doi.org/10.5772/intechopen.97481*

• M2M area Network:

**Figure 1.** *M2M architecture.*

**157**

According to [4], the M2M architecture (**Figure 1**) is divided into three domains, Devices, gateway and Network. The components of these domains are

M2M device: A device that runs one or more M2M applications using M2M service capabilities. The M2M device connect to network domain in the following for two manners, by Direct Connectivity (M2Mdevices connect to the network domain via the access network) and Gateway as a Network Proxy (The M2M device connects to the network domain via an M2M gateway);

• M2M Gateway: object that runs M2M applications, using M2M services and

Core network: Its main function is to ensure the functioning of the network with connectivity via IP and other means of connectivity, as well as control

Access network allows M2M devices and gateways to communicate with the core network. According to [5], examples of M2M include technologies such as IEEE 802.15.1, Bluetooth, personal area network, among others, or local networks such as power line communication with PLC and Wireless M-BUS;

M2M Network Area: provides the connection between devices and gateways;

Network Management: brings together all the functions necessary to manage

M2M management roles: Consist of the roles needed to manage service

Provide M2M functions that are shared by different applications;

M2M applications: run the service logic;

the network core and the access network;

capabilities within the network domain;

acting as a proxy between M2M devices and the network domain;

functions of network services, interconnection and roaming;

Distributed production systems, often composed of robot machines, are designed with the objective of providing efficiency and rationality in the use of distributed production resources, in order to favor the manufacture of products, in a dynamic and fast way. The production units must be able to respond, in an intelligent and effective manner, to unforeseen disturbances in the external environment, maintaining controlled and continuous production [3]. Considering the need to plan and control systems for these units, complete robotization of productive systems, which in turn need means or protocols of interaction and coordination between them.

Therefore, the justification for proposing this chapter is to deepen the studies on the interaction protocols for existing multi-robot systems and to design a new protocol that can be applied to concepts related to Industry 4.0, taking into account the characteristics of self- organization of robotics structure based on the concept of industrial agents.

This chapter is divided as follows. In Section 2, the Machine-to-Machine (M2M) is presented, with its levels explained. In Section 3, protocols MQTT and CoAP are presented, identifying their main characteristics and limitations. A comparison between the protocols (MQTT and CoAP) will be demonstrated in the Section 4. Section 5 is shown some studies that used MQTT protocol, along with Robot Operating System (ROS) in the context of Insdustry 4.0, in addition to presenting the conclusions of the chapter.

## **2. Machine-to-machine communications**

According to [4] the term M2M Communications, it is the machine to machine communication, which enables the transmission of data across different devices without the need for human intervention.

This communication opens up an immense range of applications that can, among other things, register, process and manipulate the data generated and transmitted by the objects that are interconnected. For example, an application that continuously receives data from a sensor that measures the temperature of an environment and, based on the data obtained, can generate statistics that describe the sensor readings over a period of time and then send an alert via e-mail or Short Message Service (SMS) to one or more individuals if the temperature has reached very high levels, or even publish this information to another device that could use it in another way, among other things.

M2M applications have the potential to become a trend in the development of software in the coming years in view of the various sectors (such as industrial and home automation) that need an automated solution that integrates the devices that are part of their environment. Devices that are part of an M2M network have the ability to at least collect data from a given environment and transmit it to an application through a connection. Eventually, these devices will not be able to transmit this data directly to other equipment, it is necessary to use a gateway to be an intermediary for this transmission.

Thus, the M2M can be defined as a number of technologies that aims to establish communication between devices with the ability to transmit information for a particular application without the interference of a human action.
