Obsidean_VM/.obsidian/plugins/text-extractor/cache/a6b4a66b7a632d90c7de90384ec2bfcf.json

{"path":"Investigar/MQTT/adjuntos/109748872_MQTT_Client_DOKU_V3-0_en.pdf","text":"MQTT Client for SIMATIC S7-1500 and S7-1200 Blocks for S7-1500 and S7-1200 https://support.industry.siemens.com/cs/ww/en/view/109748872 Siemens Industry Online Support Legal information LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 2 © Siemens AG 2021 All rights reserved Legal information Use of application examples Application examples illustrate the solution of automation tasks through an interaction of several components in the form of text, graphics and/or software modules. The application examples are a free service by Siemens AG and/or a subsidiary of Siemens AG (\"Siemens\"). They are non-binding and make no claim to completeness or functionality regarding configuration and equipment. The application examples merely offer help with typical tasks; they do not constitute customer-specific solutions. 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Table of Contents LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 3 © Siemens AG 2021 All rights reserved Table of Contents Legal information ......................................................................................................... 2 1 Introduction ........................................................................................................ 4 1.1 Overview............................................................................................... 4 1.2 Principle of Operation ........................................................................... 6 1.3 Components Used ................................................................................ 7 2 Engineering ........................................................................................................ 9 2.1 Block Description .................................................................................. 9 2.2 Configuration ...................................................................................... 10 2.2.1 Create TIA Portal Project ................................................................... 10 2.3 Integration of the Function Block in the User Program ...................... 11 2.3.1 Opening the \"LMQTT\" Global Library ................................................ 11 2.3.2 Copying Function Blocks and Data Types to the User Program ....... 13 2.3.3 Creating Global Data Block ................................................................ 14 2.3.4 Calling Function Blocks in the User Program .................................... 19 2.4 Configuration of the Security Feature ................................................ 21 2.4.1 Using the TIA Portal Global Certificate Manager ............................... 22 2.4.2 Using the Local CPU Certificate Manager ......................................... 26 2.5 Parameterization and Operation ........................................................ 29 2.6 Error Handling .................................................................................... 35 3 Useful Information ........................................................................................... 36 3.1 Fundamentals of MQTT ..................................................................... 36 3.1.1 Terminology ........................................................................................ 36 3.1.2 Standard and Architecture.................................................................. 37 3.1.3 Features ............................................................................................. 38 3.1.4 Structure of the MQTT Control Packets ............................................. 40 3.1.5 MQTT Connection .............................................................................. 41 3.1.6 MQTT Push Mechanism ..................................................................... 44 3.1.7 MQTT Sub-Mechanism ...................................................................... 47 3.1.8 MQTT Ping Mechanism ...................................................................... 50 3.1.9 MQTT Disconnection .......................................................................... 51 3.2 How the FB \"LMQTT_Client\" Works .................................................. 52 3.2.1 Requirements and Implementation .................................................... 52 3.2.2 State Machine \"STATE_MACHINE_FUNCION_BLOCK_TCP\" ........ 53 3.2.3 State Machine \"MQTT_STATE_MACHINE\" ...................................... 55 3.2.4 State Machine \"MQTT_COMMANDS\" ............................................... 56 3.2.5 Function Diagram ............................................................................... 60 4 Appendix .......................................................................................................... 61 4.1 Service and support ........................................................................... 61 4.2 Industry Mall ....................................................................................... 62 4.3 Links and literature ............................................................................. 63 4.4 Change documentation ...................................................................... 63 1 Introduction LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 4 © Siemens AG 2021 All rights reserved 1 Introduction 1.1 Overview Motivation Digitization has a major impact on the economy and society and is progressing inexorably. The \"Internet of Things\" (short: IoT) is one of the main drivers of digitization. The term \"Internet of Things\" is synonymous with one of the biggest current dynamics of change: the increasing networking and automation of devices, machines and products. The protocol \"Message Queue Telemetry Transport\" (short: MQTT) is used in the \"Internet of Things\" as a communication protocol. Its lightweight approach opens up new possibilities for automation. Slim and quick: MQTT The MQTT is a simple built-in binary publish and subscribe protocol at the TCP/IP level. It is suitable for messaging between low-functionality devices and transmission over unreliable, low-bandwidth, high-latency networks. With these characteristics, MQTT plays an important role for IoT and in M2M communication. Criteria of MQTT The MQTT protocol is distinguished by the following criteria: • Lightweight protocol with low transport overhead • Minimal need for network bandwidth through push mechanism • Function for re-connection disconnection • Re-sending messages after disconnection • Mechanism for notifying interested parties after an unpredicted disconnection of a client • Simple use and implementation thanks to a small set of commands • Quality of Serice (QoS level) with different reliability levels for the message delivery • Optional encryption of messages with SSL/TLS • Authentication of publishers and subscribers with username and password Applicative implementation To implement the MQTT protocol in a SIMATIC S7 Controller, the \"LMQTT\" library offers an adequate solution. The \"LMQTT\" library provides a function block for the SIMATIC S7-1500 and SIMATIC S7-1200. The function block \"LMQTT_Client\" integrates the MQTT Client function and allows you to submit MQTT messages to a broker (Publisher role) and to create subscriptions (Subscriber role). The communication can be secured via a TLS connection. 1 Introduction LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 5 © Siemens AG 2021 All rights reserved Figure 1-1 Note The MQTT Client supports MQTT protocol version 3.1.1. 1 Introduction LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 6 © Siemens AG 2021 All rights reserved 1.2 Principle of Operation Schematic representation The following figure shows the most important relationships between the components involved and the steps required for secured MQTT communication (MQTT over TLS). Figure 1-2 MQTT Broker MQTT-Server Certificate Store idx Cert_Name STEP 7 (TIA Portal) S7 CPU (MQTT Client) Cert_xy Cert_xy1 MQTT over TLS Engineering 1 2 3 4 Topic y Message LMQTT_ Client Connection parameters Publish Topic x Message Topic z Message Topic y Message (Un)Subscribe Table 1-1 Step Description 1 Determine the CA certificate of the MQTT Broker. 2 Importing the third-party certificate into STEP 7 (TIA Portal). The certificate is now in the global certificate manager of STEP 7. 3 You must assign the imported certificate to the S7 CPU. To recognize the certificate as valid, the time of the S7-CPU must be current. 4 The function block \"LMQTT_Client\" assumes the following roles: • Publisher to send MQTT messages to the MQTT Broker • Subscriber to subscribe to MQTT messages or end subscriptions The MQTT message is encrypted via a secure connection (MQTT over TLS). Note A more detailed functional description of the function block \"LMQTT_Client\" and information on the MQTT protocol can be found in section 3. 1 Introduction LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 7 © Siemens AG 2021 All rights reserved 1.3 Components Used The following hardware and software components were used to create this application example: Table 1-2 Components Quantity Article number Note CPU 1513-1 PN 1 6ES7513-1AL01-0AB0 • Alternatively you can use another S7 1500 CPU or ET 200 CPU (ET 200SP, ET 200pro). At least firmware version 2.0 is required for secure MQTT communication via TLS. • Alternatively, you can use an S7-1200 CPU with firmware V4.4 or higher. • Alternatively, you can also use the following components: – CP 1543-1 (6GK7543-1AX00-0XE0) with firmware V2.0 or higher – CP 1545-1 (6GK7545-1GX00-0XE0) – CP 1543SP-1 (6GK7543-6WX00-0XE0) – CP 1243-1 (6GK7243-1BX30-0XE0) with firmware V3.2 or higher – CP 1243-8 IRC (6GK7243-8RX30-0XE0) with firmware V3.2 or higher – CP 1243-7 LTE (6GK7243-7KX30-0XE0 / 6GK7243-7SX30-0XE0) with firmware V3.2 or higher TIA Portal V16 - DVD: 6ES7822-1AA06-0YA5 Download: 6ES7822-1AE06-0YA5 - MQTT Broker - - If you want to encrypt the communication, the MQTT Broker must support SSL/TLS. This application example consists of the following components: Table 1-3 Components File name \"LMQTT\" library 109780503_Libraries_Comm_Controller_LIB_V1_0_0.zip This document 109748872_MQTT_Client_DOKU_V3-0_de.pdf 1 Introduction LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 8 © Siemens AG 2021 All rights reserved Note With S7-1500 CPUs (firmware V2.0 or higher) or S7-1200 CPUs (firmware V4.4 or higher), you can reach the MQTT Broker via a static IP address or a domain name (\"Qualified Domain Name\", short: QDN) if you use the \"LMQTT\" library. 2 Engineering LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 9 © Siemens AG 2021 All rights reserved 2 Engineering Note The engineering in this section focuses on the MQTT Client function, which realizes this application example. It is assumed that you have already installed and configured the MQTT Broker. 2.1 Block Description You can find the module description in the following entry: https://support.industry.siemens.com/cs/ww/en/view/109780503 2 Engineering LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 10 © Siemens AG 2021 All rights reserved 2.2 Configuration The application example in entry 109748872 shows the configuration. 2.2.1 Create TIA Portal Project 1. Create a TIA Portal project with the CPU that you want to use for the application example. 2. Parameterize the Ethernet interface of the CPU with an IP address that lies in the same subnet as the MQTT Broker. 3. If you are using a cloud service like AWS, parameterize a router and a DNS server. 4. Connect the CPU and the MQTT Broker via Ethernet. Note For secured MQTT communication via TLS, you need an S7-1500 CPU with firmware version 2.0 or higher, or an S7-1200 CPU with firmware V4.4 or higher. 2 Engineering LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 11 © Siemens AG 2021 All rights reserved 2.3 Integration of the Function Block in the User Program The block \"LMQTT_Client\" and the required data types are available in the \"LMQTT\" library. 2.3.1 Opening the \"LMQTT\" Global Library Note For this section, you must download the \"109780503_Libraries_Comm_Controller_LIB_V1_0_0.zip\" library and unzip it into a directory of your choice. The 109780503_Libraries_Comm_Controller_LIB_V1_0_0.zip library can be found in the following entry: https://support.industry.siemens.com/cs/ww/en/view/109780503 1. In the TIA Portal project, click the \"Libraries\" task card and open the \"Global Libraries\" palette. 2. Click on the \"Open global library\" button. The “Open global library” dialog is opened. 2 Engineering LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 12 © Siemens AG 2021 All rights reserved 3. Select the global library \"Libraries_Comm_Controller\" and confirm the selection with the \"Open\" button. 4. The \"Libraries_Comm_Controller\" library opens and appears under the Global libraries palette. 2 Engineering LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 13 © Siemens AG 2021 All rights reserved 2.3.2 Copying Function Blocks and Data Types to the User Program 1. In the \"Libraries_Comm_Controller\" library, you will find the FB \"LMQTT_Client\" and the corresponding PLC data types under \"Types > LMQTT\". 2. Insert the function block for your CPU via drag & drop into the folder \"Program blocks\" of your device, e.g. S7-1500 CPU. 2 Engineering LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 14 © Siemens AG 2021 All rights reserved 3. The data types used by the FB \"LMQTT_Client\" are automatically inserted into the folder \"PLC data types\" on your device (e.g., an S7-1500 CPU). 2.3.3 Creating Global Data Block This section shows you how to create a global data block (DB). This DB is used to store the following data: • TCP connection parameters • MQTT connection parameters • Topic and message to be sent to the MQTT Broker (publish) • Received data, i.e. message and name of the subscribed topic (subscribe) 1. Navigate in the \"Project tree\" to the device folder of the CPU. 2. Open the \"Program blocks\" folder and double-click the \"Add new block\" command. The dialog \"Add new block\" opens. 2 Engineering LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 15 © Siemens AG 2021 All rights reserved 3. Make the following settings and then confirm your entries with the \"OK\" button. – Select the symbol \"Data block\". – Select \"Global DB\" as the type. – Enter the name of the DB. – Enable the \"Automatic\" radio button for automatic number assignment. The number of the global DB is assigned by the TIA Portal. 2 Engineering LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 16 © Siemens AG 2021 All rights reserved 4. Double-click the newly inserted global data block to open it. 5. Double-click \"<Add new>\" to add the corresponding tags. 2 Engineering LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 17 © Siemens AG 2021 All rights reserved Result The following figure shows the tags in the DB \"MqttDb\" for switching the inputs and outputs of the FB \"MQTT_Client\". Figure 2-1 2 Engineering LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 18 © Siemens AG 2021 All rights reserved The following figure shows the parameters of the tag \"connparams\". Figure 2-2 2 Engineering LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 19 © Siemens AG 2021 All rights reserved 2.3.4 Calling Function Blocks in the User Program 1. In the \"Project tree\" open the folder \"Program blocks\" of your CPU 2. Double-click the block \"Main [OB1]\" to open the corresponding program editor. 3. Drag & drop the FB \"LMQTT_Client\" from the project navigation to any OB1 network. 4. The dialog \"Call options\" for generating the instance DB of the FB \"LMQTT_Client\" opens automatically. 5. Make the following settings and then confirm your entries with the \"OK\" button. – Enter the name of the instance DB. – Enable the \"Automatic\" radio button for automatic number assignment. The number of the instance DB is assigned by the TIA Portal. – Click \"OK\" to confirm the settings. 6. Assign the tags that you have created in the global data block to the inputs and outputs of the FB (see section 2.3.3). 2 Engineering LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 20 © Siemens AG 2021 All rights reserved Result The following figure shows the linking of the DB \"MqttDb\" tags on the FB \"MQTT_Client\". Figure 2-3 2 Engineering LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 21 © Siemens AG 2021 All rights reserved 2.4 Configuration of the Security Feature Note You only need to configure the security feature if you are using a secure MQTT connection via TLS. Note In this application example, the MQTT Broker does not authenticate the MQTT Client. Only the CA certificate of the MQTT Broker is required to authenticate the MQTT Broker. If you have configured the MQTT Broker to require MQTT Client authentication, you must also import the client certificate. The client certificate must be signed by the same CA as the server certificate. Encryption via SSL/TLS works via certificates. A certificate is a public key signed by its owner that guarantees its authenticity and integrity. To authenticate the broker, the MQTT Client requires the CA certificate of the broker. This section shows you how to import the certificate of the MQTT Broker into the CPU (MQTT Client). Encrypted MQTT communication is only possible with this certificate. Requirement for TLS/SSL encryption To set up a secure MQTT communication between the SIMATIC S7 CPU (MQTT Client) and an MQTT Broker in your network, the following points must be fulfilled: • The MQTT Broker is installed and preconfigured for the TLS procedure. • The necessary CA certificate of the MQTT Broker is available to you. • The time of the CPU is set to the current time. A certificate always contains a period of time in which it is valid. To be able to encrypt with the certificate, the time of the S7 CPU must also be within this period. With a brand new S7-CPU or after an overall reset of the S7-CPU, the internal clock is set to a default value that lies outside the certificate runtime. The certificate is then marked as invalid. 2 Engineering LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 22 © Siemens AG 2021 All rights reserved 2.4.1 Using the TIA Portal Global Certificate Manager You must import the CA certificate of the MQTT Broker into STEP 7 (TIA Portal). In the TIA Portal, the certificates are managed in the global certificate manager. The certificate manager contains an overview of all certificates used in the project. In the certificate manager, for example, you can import new certificates and export, renew, or replace existing certificates. Each certificate is assigned an ID that can be used to reference the certificate in the program blocks. Activating the global certificate manager If you do not use the certificate manager in the security settings, you only have access to the local certificate store of the CPU. You then have no access to imported certificates from external devices. To import and use the CA certificate of the MQTT Broker, you must activate the global certificate manager. 1. In the Device or Network view select the CPU. The properties of the CPU are displayed in the Inspector window. 2. In the area navigation of the \"Properties\" tab, select \"Protection & Security > Certificate Manager\". Enable the option \"Use global security settings for certificate manager\". Result The new entry \"Security Settings\" appears in the project navigation. 2 Engineering LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 23 © Siemens AG 2021 All rights reserved Logging on users After you have enabled the global security settings for the certificate manager, you must log in to the security settings. You cannot access the global certificate manager without logging in. Log on as a security user for the security settings as described below: 1. Double-click the entry \"Settings\" in the project navigation under \"Security settings\". 2. The user administration editor opens and the project protection area is displayed. Click the \"Protect this project\" button. 3. This opens the dialog \"Protect Project\". Enter a username and password. The password must comply with the following guidelines: – Password length: A minimum of eight characters, a maximum of 128 characters – At least one upper-case letter – At least one special character (special characters § and ß are not allowed) – At least one number Enter the password again to confirm. 2 Engineering LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 24 © Siemens AG 2021 All rights reserved 4. You may enter a comment if required. Confirm your entries with \"OK\". Result You have activated the user administration. You are logged in as a project administrator and can use the security settings. If you have logged in, a line \"Certificate manager\" appears under the entry \"Security settings > Security features\". Figure 2-4 2 Engineering LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 25 © Siemens AG 2021 All rights reserved Using the global certificate manager With the global certificate manager, you now have the option of importing third- party certificates into TIA Portal. By double-clicking on the line \"Certificate manager\" you gain access to all certificates in the project, divided into the following tabs: • \"Certificate Authority (CA)\" • \"Device certificates\" • \"Trusted certificates and core certification authorities\" 1. Double-click the \"Certificate manager\" entry in the project navigation under \"Security settings > Security features\". 2. Select the appropriate registry for the certificate you want to import, for example, \"Trusted certificates and core certification authorities\". 3. To open the context menu, right-click in the tab. Click \"Import\". 4. Select the export format of the certificate: – CER, DER, CRT or PEM for certificates without a private key – P12 (PKCS12 archive) for certificates with a private key. Click on \"Open\" to import the certificate. Result The CA certificate of the MQTT Broker is now located in the global certificate manager. Figure 2-5 2 Engineering LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 26 © Siemens AG 2021 All rights reserved Note If the MQTT Broker also requires authentication of the MQTT Client, you must import the client certificate. Observe the following information: • The client certificate must be signed by the same CA as the server certificate. • The client certificate must be imported as a PK12 container (with certificate and private key) into the global certificate manager. • The client certificate must be imported into the \"Device certificates\" table. 2.4.2 Using the Local CPU Certificate Manager The CA certificate is currently only located in the global certificate manager of the TIA Portal. Certificates imported via the certificate manager into the global security settings are not automatically assigned to the corresponding modules. To authenticate the MQTT Broker, you have to load the CA certificate into the CPU. Only those device certificates that you have assigned to the module as device certificates via the local certificate manager are loaded onto the module. This assignment is made in the local security settings of the module in the entry \"Certificate manager\" via the table editor \"Device certificates\". The certificates of the global certificate manager are available for the certificate assignment. The following steps show you how to assign the CA certificate from the global certificate manager to the CPU. 1. In the Device or Network view select your CPU. The properties of the CPU are displayed in the Inspector window. 2. To add the CA certificates, select the entry \"Certificate manager\" in the area navigation of the \"Properties\" tab under \"Protection & Security\". 3. Under \"Certificates of the partner devices\". Click \"Add\" in the table of certificates. This inserts a new row into the table. 2 Engineering LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 27 © Siemens AG 2021 All rights reserved 4. Click in the new row. The selection for new certificates opens. Select the previously imported CA certificate from the global certificate manager and click the green check mark. 2 Engineering LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 28 © Siemens AG 2021 All rights reserved Result The selected certificate was assigned to the CPU and provided with an ID. The ID is the number of the certificate. Enter this value in the connection parameters for the \"brokerCert\" parameter (see Figure 2-2). Figure 2-6 Note If the MQTT Broker additionally requires authentication of the MQTT Client, you must also assign the imported client certificate to the CPU (section \"Device certificates\"). Enter the value of the ID in the connection parameters for the \"clientCert\" parameter (see Figure 2-2). 2 Engineering LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 29 © Siemens AG 2021 All rights reserved 2.5 Parameterization and Operation Setting the parameters Before you can test the application example, you must first set the parameters for the secured or unsecured TCP connection and for MQTT corresponding to your specifications. All parameters that you can define yourself are located in the global data block \"MqttDb\". Set the parameters in the \"Start value\" column. Connect the tags of the data block \"MqttDb\" with the inputs and outputs of the FB \"LMQTT_Client\". Above all, you must enter your own value for the following parameters: • Connection number • IPv4 address or domain name of the MQTT Broker. The domain name must end with a \".\". • Port on which the MQTT Broker receives the messages – unsecured connection: remote port 1883 – secured connection: remote port 8883 • Parameters for secure communication – Status of the security feature (On/Off) for this connection – ID of the CA certificate (only relevant for a secure connection) – ID of your own certificate, if the MQTT Broker also authenticates the client (only relevant for a secure connection) • MQTT parameters, e.g. – Login information for the MQTT Broker – Topic – Message text Then load the project into your CPU. 2 Engineering LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 30 © Siemens AG 2021 All rights reserved The following table shows the tags in the DB \"MqttDb\" to interconnect the inputs and outputs of the FB \"MQTT_Client\". Table 2-1 Tag Data type Note control Struct This data structure contains the tags for controlling the jobs of the FB \"LMQTT_Client\". connect Bool This tag controls the connection establishment. • Set the tag to the value \"1\" to establish the TCP and MQTT connection. • If the value of the tag changes from \"1\" to \"0\" (negative edge), the TCP and MQTT connection is disconneted. publish Bool Use this tag to start a job to send a PUBLISH packet. subscribe Bool Use this tag to start a job to send a SUBSCRIBE packet. unsubscribe Bool Use this tag to start a job to send a UNSUBSCRIBE packet. output Struct This data structure contains the tags for evaluating the outputs of the FB \"LMQTT_Client\". valid Bool Status display True: The values for the outputs of the FB \"LMQTT_Client\" are valid. done Bool Status display • True: Job executed with no errors. • False: Job not yet started or still processing. busy Bool Status display • True: Job not finished yet. A new job cannot be started. • False: Job not yet started or already finished. error Bool Status display • True: Error occurred • False: No error status Word Status of the FB \"LMQTT_Client\" Detailed information can be found in the library description in entry 109780503. diagnostics \"typeDiagnostics\" Diagnostic information of the FB \"LMQTT_Client\" Detailed information can be found in the library description in entry 109780503. 2 Engineering LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 31 © Siemens AG 2021 All rights reserved Tag Data type Note connparams \"LMQTT_type_connparams\" Enter the parameters to establish a connection to the MQTT Broker. Detailed information can be found in Table 2-2. clientid WString[20] Enter the Client identifier that is used when establishing the connection (e.g., \"SiemensClient\"). username WString[20] Optionally, it is possible to enter a username for the connection setup. If no username is entered, the parameter is not evaluated. password WString[20] Optionally, it is possible to enter a password for the connection setup. If no password is entered, the parameter is not evaluated. willtopic WString[20] Optionally, it is possible to enter a topic to which the \"Last Will\" message will be sent. willMessage Array[*] of Byte Optionally, it is possible to enter a message that will be sent as the \"Last Will\". The length of the array can be chosen as desired. The real message length sent from this array is specified by the tag \"willmesscnt\". willmesscnt UInt Current length of valid data in the array \"willMessage\". qos USInt Enter the Quality of Service with which the messages are sent. Possible values are 0, 1, or 2. topic WString[100] Enter the MQTT topic that will be used in the publish, subscribe, or unsubscribe job. message Array[*] of Byte Enter the MQTT message that is transmitted as user data in the publish job. The length of the array can be chosen as desired. The real message length sent from this array is specified with the tag \"pubMessageCnt\". pubMessageCnt UDInt Current length of valid data in the array \"message\". 2 Engineering LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 32 © Siemens AG 2021 All rights reserved Tag Data type Note retain Bool Enter whether the data is sent with or without the \"retain\" flag. • True: The data is sent with the \"retain\" flag. • False: The data is sent without the \"retain\" flag. receivedTopic WString[200] The MQTT topic on which a message is received regarding the subscription is stored in this tag. receivedmessage Array[*] of Byte This tag stores the user data received in the message via a subscription. The length of the array can be chosen as desired. The real message length received in this array is shown in the tag \"receivedMsgLen\". receivedMsgLen UDInt Number of valid data in the array \"receivedmessage\". receivedMsgStatus USInt This tag indicates, for one cycle at a time, when a new message has been received (subscription). • 0: No new message received. • 1: New valid message received. • 2: New message received, but message invalid or received data is larger than the memory area of the receive topic or receive message. 2 Engineering LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 33 © Siemens AG 2021 All rights reserved The following table shows the parameters of the tag \"connparams\". Table 2-2 Parameters Data type Note hwId HW_ANY Enter the hardware identifier of the PN/IE interface for establishing the connection. If the tag has the value \"0\", a suitable hardware identifier is automatically selected. connId CONN_OUC Connection ID for establishing the connection. mqttBrockerAddress Struct This data structure contains the address parameters of the MQTT Broker. qdnAddress String Enter the domain name of the MQTT Broker. The domain name must end with a \".\". If this parameter is used, the IP address entry can be omitted. ipAddress IP_V4 Enter the IP address of the MQTT Broker. port UInt Enter the MQTT port. • Port 1883: unsecured connection • Port 8883: secured connection tls Struct This data structure contains the parameters for a secure connection. enableTls Bool Enter the value \"True\" if the connection will be secured with TLS. validateServerIdentity Bool Enter the value \"True\" if the certificate of the MQTT Broker will be validated when establishing the connection. brokerCert UDInt Certificate ID of the MQTT Broker certificate. clientCert UDInt Certificate ID of the MQTT Client certificate. keepAlive UInt Enter a value in seconds for the activation of the Keep-Alive mechanism of MQTT. If the tag has the value \"0\", no Keep-Alive is active. Note If the TCP connection will be established via the fully qualified domain name, you must configure a DNS server in the CPU. 2 Engineering LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 34 © Siemens AG 2021 All rights reserved Operating the application example Once you have set all parameters and added the CA certificate of the MQTT Broker to the local certificate manager of the CPU, you can test the application example. Before you test the application example, check the following points: 1. The project is loaded into the CPU. 2. The CPU and the MQTT Broker are connected to each other and can be reached via Ethernet. 3. The MQTT Broker is properly configured and started. 4. Logging into the MQTT Broker is started as needed to support the logon of the MQTT Client and the publish mechanism. If the above points are met, you can initiate MQTT communication between the CPU and the MQTT Broker. For this, trigger the input \"enable\" of the function block \"LMQTT_Client\". As long as the input \"enable\" is set to \"True\", the connection is maintained. If the input \"enable\" is reset to \"False\", the connection is disconnected. In the positive case, the internal state machines will loop through and establish a TCP and MQTT connection to the MQTT Broker. The output tag \"status\" is set to the value \"16#7004\" and signals an existing TCP and MQTT connection. Now you can perform the following functions: • Send MQTT message: Trigger the input tag \"publish\". • MQTT message received for a subscribed topic: Trigger the input tag \"subscribe\". If the connection to the MQTT Broker is interrupted (status = 16#9000), the connection is automatically re-established. After a disconnection, it is necessary to perform a \"subscribe\" job for the subscribed topics. • Unsubscribe yourself from subscribed topics: Trigger the tag \"unsubscribe\". If the connection to the MQTT Broker is not established, check the output tag \"status\" and \"diagnostics\" to diagnose the error. 2 Engineering LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 35 © Siemens AG 2021 All rights reserved 2.6 Error Handling For information on the meaning of the values of the tags \"status\" and \"diagnostics\", see the library description in the following entry: https://support.industry.siemens.com/cs/ww/en/view/109780503 3 Useful Information LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 36 © Siemens AG 2021 All rights reserved 3 Useful Information 3.1 Fundamentals of MQTT Note A detailed description of MQTT can be found in the MQTT specification description (see \\3\\ in section 4.3). 3.1.1 Terminology The most important terms in the MQTT telemetry protocol are explained below. MQTT message A message with MQTT consists of several parts: • A defined subject (\"Topic\") • An assigned criterion for \"Quality of Service\" • The message text MQTT Client An MQTT Client is a program or device that uses MQTT. A client always actively establishes the connection to the broker. A client can perform the following functions: • Send messages with a defined subject (\"Topic\"), in which other clients might be interested, to the MQTT Broker (Publish mechanism) • Subscribe messages which follow a certain topic (Subscriber mechanism) at the MQTT Broker • Unsubscribe yourself from subscribed messages • Disconnect from the broker Note The function block \"LMQTT_Client\" in this application example supports the following functions: • Logging into the MQTT Broker • Publish mechanism • Subscribe and unsubscribe mechanisms • Ping mechanism • Unsubscribe from the MQTT Broker. 3 Useful Information LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 37 © Siemens AG 2021 All rights reserved MQTT Broker An MQTT Broker is the central component of MQTT and can be a program or a device. The MQTT Broker acts as an intermediary between the sending MQTT Client and the subscribing MQTT Client. The MQTT Broker manages the topics including the messages contained therein and regulates the access to the topics. The MQTT Broker has the following functions: • Accept network connections from the MQTT Clients • Receive messages from an MQTT Client • Edit subscription requests from MQTT Clients • Forward messages to the MQTT Clients that match your subscription Note The MQTT Broker is not part of this application example and is assumed to be given. Topics MQTT messages are organized in topics. A topic \"describes\" a subject area. The topics can be subscribed to by the MQTT Clients (subscriber mechanism). The sender of a message (Publisher mechanism) is responsible for defining content and topic when sending the message. The broker then takes care that the Subscribers get the news from the subscribed topics. The topics follow a defined scheme. They are similar to a directory path and represent a hierarchy. 3.1.2 Standard and Architecture ISO standard MQTT defines an OASIS or ISO standard (ISO/IEC PRF 20922). Depending on the security protocols used, MQTT runs on different access ports. Ports offered are: • 1883: MQTT, unencrypted • 8883: MQTT, encrypted • 8884: MQTT, encrypted, Client Certificate required • 8080: MQTT via WebSockets, unencrypted • 8081: MQTT via WebSockets, encrypted Architecture The MQTT is a publish and subscribe protocol. This mechanism decouples a client sending messages (Publishers) from one or more clients receiving the messages (Subscribers). This also means that the \"Publishers\" know nothing about the existence of the \"Subscribers\" (and vice versa). There is a third component in the MQTT architecture, the MQTT Broker. The MQTT Broker is located between \"Publisher\" and \"Subscriber\". The MQTT Broker controls the communication. 3 Useful Information LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 38 © Siemens AG 2021 All rights reserved 3.1.3 Features MQTT offers quite useful features. Quality of Service The MQTT specification provides three service qualities for message transmission quality assurance: • QoS \"0\": The lowest level 0 is a \"fire'n'forget\" method. This means that there is no guarantee that the message will arrive at all. • QoS \"1\": The QoS level 1 ensures that the message ends up in the topic queue at least once. The MQTT Broker acknowledges receipt of the message. • QoS \"2\": In the highest level 2, the MQTT Broker guarantees by multiple handshake with the MQTT Client that the message is exactly filed once. Last will MQTT supports the \"Last Will and Testament\" feature. This feature is used to notify other MQTT Clients if the connection to a MQTT Client has been disconnected accidentally. Each MQTT Client can specify its last will while connecting to the MQTT Broker and notify the MQTT Broker. This last will is built like a normal MQTT message, including topic, QoS and payload. The MQTT Broker saves the last will. As soon as the MQTT Broker notices that the connection with the MQTT Client in question has been abruptly terminated, the MQTT Broker sends the last will as an MQTT message to all subscribers who have registered for the topic. In this way, the subscribers also learn that the MQTT Client has been disconnected. Keep-Alive MQTT supports the \"Keep-Alive\" feature. This ensures that the connection is still open and the MQTT Client and MQTT Broker are connected. For the Keep-Alive, the MQTT Clients define a time interval and communicate it to the MQTT Broker during their connection setup. This interval is the largest possible tolerated time period in which the MQTT Client and the MQTT Broker may remain without contact. If the time is exceeded, the MQTT Broker must disconnect. That means that, as long as the MQTT Client periodically sends messages to the broker within the Keep-Alive interval, the MQTT Client does not need to take any special action to maintain the connection. However, if the MQTT Client does not send any messages within the Keep-Alive interval, they must ping the MQTT Broker before the deadline expires. With this ping, the MQTT Client signals to the MQTT Broker that it is still available. When a message or a ping packet has been sent to the MQTT Broker, timing for the Keep-Alive interval begins again. Note • The client determines the Keep-Alive interval. It can therefore adjust the interval of his environment, e.g. because of a slow bandwidth. • The maximum value for the Keep-Alive interval is 18 h 12 m 15 s. • When the client sets the Keep-Alive interval to \"0\", the Keep-Alive mechanism is disabled. 3 Useful Information LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 39 © Siemens AG 2021 All rights reserved Message persistence If the connection to an MQTT Client is interrupted, the broker can cache new messages for this client for later delivery. Retained messages The first time an MQTT Client subscribes to a topic, it usually gets a message only when another MQTT Client sends a message with the subscribed topic the next time. With \"Retained messages\", the subscriber receives the last value sent to the topic prior to its subscription request, delivered immediately. 3 Useful Information LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 40 © Siemens AG 2021 All rights reserved 3.1.4 Structure of the MQTT Control Packets Most MQTT control packets work according to the handshake procedure. The MQTT Client is always the active element and creates a job for the MQTT Broker. The broker confirms the request depending on the job. The structure of an MQTT control packet is fixed. The following diagram shows the structure: Figure 3-1 Fixed header Mandatory for all control packages Variable header Mandatory for some control packages Payload Mandatory for all control packages The \"Fixed header\" always consists of the following elements: • An identifier number for the MQTT control packet type • An area for possible flags; if no flags are provided for the control packet, the bits are marked as \"reserved\" • The number of following bytes after the \"Fixed header\" The \"Variable header\" is required only for some control packets. The content of the variable header depends on the control packet type. The payload is mandatory for most control packets. Again, the content depends on the control packet type. For each type of control packet, there are clear rules with what and in what order the payload can be filled. Note A detailed description of MQTT control packets can be found in the MQTT specification description (see \\3\\ in section 4.3). The MQTT control packets from this application example are briefly explained below. 3 Useful Information LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 41 © Siemens AG 2021 All rights reserved 3.1.5 MQTT Connection An MQTT connection is always made between an MQTT Client and the MQTT Broker. A direct client-client connection is not possible. The connection is initiated by an MQTT Client as soon as the MQTT Client sends a \"CONNECT\" packet to the MQTT Broker. If positive, the MQTT Broker replies with a \"CONNACK\" packet and a status code. The MQTT Broker immediately closes the connection in the following cases: • If the \"CONNECT\" packet is faulty • If the structure of the \"CONNECT\" packet does not meet the specification • If the connection takes too long MQTT control packet \"CONNECT\" Table 3-1 shows the structure of the \"fixed header\" of the \"CONNECT\" packet. Table 3-1 Fixed header Bit 7 6 5 4 3 2 1 0 Byte 1 Identifier number for MQTT control packet type = 1 (dec) Reserve Byte 2 Remaining length: The number of following bytes after the \"fixed header\" = \"variable header\" + \"payload\" A \"CONNECT\" packet contains the following areas in the \"variable header\": 1. Report name: The report name \"MQTT\" is transmitted as UTF-8 string. 2. Report level: 4 (dec) 3. Connect flags: The \"Connect Flags\" byte contains a number of parameters that specify the behavior of the MQTT connection. In addition, the \"Connect Flags\" byte also shows which optional fields are present in the \"payload\" or not. The connection type can be regulated with the \"Clean Session\" flag. 4. Keep alive: The Keep-Alive time determines the time interval in which the MQTT Client is obligated to report to the MQTT Broker. This can be done either by sending a message or a PING command. If the client does not report in the time interval, the MQTT Broker disconnects from the client. 3 Useful Information LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 42 © Siemens AG 2021 All rights reserved Table 3-2 shows the structure of the \"variable header\" of the \"CONNECT\" packet. Table 3-2 Variable header Bit 7 6 5 4 3 2 1 0 Report name Byte 1 MSB length = 0 (dec) Byte 2 LSB length = 4 (dec) Byte 3 'M' 0 1 0 0 1 1 0 1 Byte 4 'Q' 0 1 0 1 0 0 0 1 Byte 5 'T' 0 1 0 1 0 1 0 0 Byte 6 'T' 0 1 0 1 0 1 0 0 Report level Byte 7 Report level = 4 (dec) Connect flags Byte 8 User name flag Password flag Will retain flag Will QoS flag Will flag Clean session flag Reserve Keep alive Byte 9 Keep alive MSB Byte 10 Keep alive LSB In \"Payload\" the existing fields appear in the following order: • Client ID: The client ID is used to identify the client at the MQTT Broker. The client ID must appear as the first field in the \"Payload\". • Will topic: The field appears optionally if the \"Will\" flag is set to \"TRUE\". • Will message: The field appears optionally if the \"Will\" flag is set to \"TRUE\". • Username: The field appears optionally if the \"Username\" flag is set to \"TRUE\". • Password: The field appears optionally if the \"Password\" flag is set to \"TRUE\". 3 Useful Information LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 43 © Siemens AG 2021 All rights reserved MQTT control packet \"CONNACK\" Table 3-3 shows the structure of the \"fixed header\" of the \"CONNACK\" packet: Table 3-3 Fixed header Bit 7 6 5 4 3 2 1 0 Byte 1 Identifier number for MQTT control packet type = 2 (dec) Reserve Byte 2 Remaining length: The number of following bytes after the \"fixed header\" = \"variable header\" = 2 bytes Table 3-4 shows the structure of the \"variable header\" of the \"CONNACK\" packet. Table 3-4 Variable header Bit 7 6 5 4 3 2 1 0 Connect acknowledge flags Byte 1 Reserve Session Present Connect Return Code Byte 2 • 0x00 = The MQTT Broker accepts the connection. The MQTT Broker does not support the level of the MQTT protocol requested by the client. • 0x01 = The MQTT Broker does not support the level of the MQTT protocol requested by the MQTT Client. • 0x02: The MQTT Broker does not allow the client ID. • 0x03: The MQTT service is not available. • 0x04: The data in the username and password are incorrect. • 0x05: The MQTT Client is not authorized to connect. 3 Useful Information LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 44 © Siemens AG 2021 All rights reserved 3.1.6 MQTT Push Mechanism Once an MQTT Client connects to the MQTT Broker, it can send messages to the MQTT Broker. To do this, the client uses the \"PUBLISH\" packet. Because MQTT messages are filtered and managed based on topics, each MQTT message must contain a topic. The topic is part of the \"Variable Header\". The actual message text is contained in the \"payload\". \"PUBLISH\" packet Table 3-5 shows the structure of the \"fixed header\" of the \"PUBLISH\" packet. Table 3-5 Fixed header Bit 7 6 5 4 3 2 1 0 Byte 1 Identifier number for MQTT control packet type = 3 (dec) DUP flag QoS level Retain flag 0 0 1 1 X X X X Byte 2 Remaining length: The number of following bytes after the \"fixed header\" = \"variable header\" + payload Depending on the quality assurance setting (\"QoS\"), the push mechanism ends at this point or other control packets are exchanged: • QoS = 0 (dec): The message will be sent only once. The send job ends here. • QoS = 1 (dec): The message will be sent at least once. The MQTT Broker acknowledges the \"PUBLISH\" packet with a \"PUBACK\" packet. • QoS = 2 (dec): The message will be sent exactly once. The MQTT Broker acknowledges the \"PUBLISH\" packet with a \"PUBREC\" packet. This is followed by another handshake between MQTT Client and MQTT Broker. The client answers the \"PUBREC\" packet with a \"PUBREL\" packet. The MQTT Broker completes the double handshake with a \"PUBCOM\" packet. Note You can find further information on Quality Assurance QoS in section 3.1.3. The \"variable header\" of the \"Publish\" packet contains the following fields: • Name of the topic • Packet ID The \"Payload\" contains the message text. 3 Useful Information LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 45 © Siemens AG 2021 All rights reserved \"PUBACK\" packet (Publish Acknowledgement) The MQTT Broker responds to the \"PUBLISH\" packet with QoS=1 with the \"PUBACK\" packet. Table 3-6 shows the structure of the \"fixed header\" of the \"PUBACK\" packet. Table 3-6 Fixed header Bit 7 6 5 4 3 2 1 0 Byte 1 Identifier number for MQTT control packet type = 4 (dec) Reserve 0 1 0 0 0 0 0 0 Byte 2 Remaining length: The number of following bytes after the \"fixed header\" = \"variable header\" = 2 bytes The \"variable header\" of the \"PUBACK\" packet contains the packet ID. The \"PUBACK\" packet has no \"payload\". \"PUBREC\" packet (Publish Received) The MQTT Broker responds to the \"PUBLISH\" packet with QoS=2 with the \"PUBREC\" packet. Table 3-7 shows the structure of the \"fixed header\" of the \"PUBREC\" packet. Table 3-7 Fixed header Bit 7 6 5 4 3 2 1 0 Byte 1 Identifier number for MQTT control packet type = 5 (dec) Reserve 0 1 0 1 0 0 0 0 Byte 2 Remaining length: The number of following bytes after the \"fixed header\" = \"variable header\" = 2 bytes The \"variable header\" of the \"PUBREC\" packet contains the packet ID. The \"PUBREC\" packet has no \"payload\". 3 Useful Information LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 46 © Siemens AG 2021 All rights reserved \"PUBREL\" packet (Publish Release) The MQTT Client responds to the \"PUBREC\" packet with the \"PUBREL\" packet. Table 3-8 shows the structure of the \"fixed header\" of the \"PUBREL\" packet. Table 3-8 Fixed header Bit 7 6 5 4 3 2 1 0 Byte 1 Identifier number for MQTT control packet type = 6 (dec) Reserve 0 1 1 0 0 0 1 0 Byte 2 Remaining length: The number of following bytes after the \"fixed header\" = \"variable header\" = 2 bytes Note The reserve bits in the \"fixed header\" must be set as follows: • Bit 3 = 0 • Bit 2 = 0 • Bit 1 = 1 • Bit 0 = 0 The \"variable header\" of the \"PUBREL\" packet contains the packet ID. The \"PUBREL\" packet has no \"payload\". \"PUBCOMP\" packet (Publish Complete) The MQTT Broker responds to the \"PUBREL\" packet with the \"PUBCOMP\" packet. Table 3-9 shows the structure of the \"fixed header\" of the \"PUBCOMP\" packet. Table 3-9 Fixed header Bit 7 6 5 4 3 2 1 0 Byte 1 Identifier number for MQTT control packet type = 7 (dec) Reserve 0 1 1 1 0 0 0 0 Byte 2 Remaining length: The number of following bytes after the \"fixed header\" = \"variable header\" = 2 bytes The \"variable header\" of the \"PUBCOMP\" packet contains the packet ID. The \"PUBCOMP\" packet has no \"payload\". 3 Useful Information LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 47 © Siemens AG 2021 All rights reserved 3.1.7 MQTT Sub-Mechanism Once an MQTT Client has connected to the MQTT Broker, it can create or unsubscribe from subscriptions. \"SUBSCRIBE\" packet To create a subscription, the MQTT Client uses the \"SUBSCRIBE\" packet. A list of the topics that the MQTT Client would like to subscribe to is stored in the \"Payload\". Table 3-10 shows the structure of the \"fixed header\" of the \"SUBSCRIBE\" packet. Table 3-10 Fixed header Bit 7 6 5 4 3 2 1 0 Byte 1 Identifier number for MQTT control packet type = 8 (dec) Reserve 1 0 0 0 0 0 1 0 Byte 2 Remaining length: The number of following bytes after the \"fixed header\" = \"variable header\" + \"payload\" Note The reserve bits in the \"fixed header\" must be set as follows: • Bit 3 = 0 • Bit 2 = 0 • Bit 1 = 1 • Bit 0 = 0 The \"variable header\" of the \"SUBSCRIBE\" packet contains the packet ID. Table 3-11 shows the structure of the \"payload\" of the \"SUBSCRIBE\" packet. Table 3-11 Payload Bit 7 6 5 4 3 2 1 0 Topic name Byte 1 MSB length Byte 2 LSB length Byte 3…n Topic name Requested service quality QoS Byte n+1 Reserve QoS level Possible values: • 0 (dec) • 1 (dec) • 2 (dec) 3 Useful Information LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 48 © Siemens AG 2021 All rights reserved \"SUBACK\" packet (Subscribe Acknowledgement) The MQTT Broker responds to the \"SUBSCRIBE\" packet with the \"SUBACK\" packet. Table 3-12 shows the structure of the \"fixed header\" of the \"SUBACK\" packet. Table 3-12 Fixed header Bit 7 6 5 4 3 2 1 0 Byte 1 Identifier number for MQTT control packet type = 9 (dec) Reserve 1 0 0 1 0 0 0 0 Byte 2 Remaining length: The number of following bytes after the \"fixed header\" = \"variable header\" + \"payload\" The \"variable header\" of the \"SUBACK\" packet contains the packet ID. Table 3-13 shows the structure of the \"payload\" of the \"SUBACK\" packet. Table 3-13 Payload Bit 7 6 5 4 3 2 1 0 Return code Byte 1 • 0x00: Successful: Maximum service quality QoS 0 • 0x01: Successful: Maximum service quality QoS 1 • 0x02: Successful: Maximum service quality QoS 2 • 0x80: Error \"UNSUBSCRIBE\" packet To unsubscribe from a subscription, the MQTT Client uses the \"UNSUBSCRIBE\" packet. A list of the topics that the MQTT Client would like to unsubscribe from is stored in the \"Payload\". Table 3-14 shows the structure of the \"fixed header\" of the \"UNSUBSCRIBE\" packet. Table 3-14 Fixed header Bit 7 6 5 4 3 2 1 0 Byte 1 Identifier number for MQTT control packet type = 10 (dec) Reserve 1 0 1 0 0 0 1 0 Byte 2 Remaining length: The number of following bytes after the \"fixed header\" = \"variable header\" + \"payload\" Note The reserve bits in the \"fixed header\" must be set as follows: • Bit 3 = 0 • Bit 2 = 0 • Bit 1 = 1 • Bit 0 = 0 3 Useful Information LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 49 © Siemens AG 2021 All rights reserved The \"variable header\" of the \"UNSUBSCRIBE\" packet contains the packet ID. Table 3-15 shows the structure of the \"payload\" of the \"UNSUBSCRIBE\" packet. Table 3-15 Payload Bit 7 6 5 4 3 2 1 0 Topic name Byte 1 MSB length Byte 2 LSB length Byte 3…n Topic name \"UNSUBACK\" packet The MQTT Broker responds to the \"UNSUBSCRIBE\" packet with the \"UNSUBACK\" packet. Table 3-16 shows the structure of the \"fixed header\" of the \"UNSUBACK\" packet. Table 3-16 Fixed header Bit 7 6 5 4 3 2 1 0 Byte 1 Identifier number for MQTT control packet type = 11 (dec) Reserve 1 0 1 1 0 0 0 0 Byte 2 Remaining length: The number of following bytes after the \"fixed header\" = \"variable header\" = 2 bytes. The \"variable header\" of the \"UNSUBACK\" packet contains the packet ID. The \"UNSUBACK\" packet has no \"payload\". 3 Useful Information LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 50 © Siemens AG 2021 All rights reserved 3.1.8 MQTT Ping Mechanism If the Keep-Alive interval is greater than \"0\", the Keep-Alive function is active. If the Keep-Alive function is active, the MQTT Client must send at least one message to the MQTT Broker within the Keep-Alive interval. If this is not the case, the MQTT Broker must terminate the connection to the MQTT Client. To prevent this type of forced abort, the MQTT Client must ping the MQTT Broker before the Keep-Alive time expires. The control packet \"PINGREQ\" is used for this. \"PINGREQ\" packet Table 3-17 shows the structure of the \"fixed header\" of the \"PINGREQ\" packet Table 3-17 Fixed header Bit 7 6 5 4 3 2 1 0 Byte 1 Identifier number for MQTT control packet type = 12 (dec) Reserve 1 1 0 0 0 0 0 0 Byte 2 Remaining length: The number of following bytes after the \"fixed header\" = 0 bytes. The \"PINGREQ\" packet has no \"variable header\" and no \"payload\". \"PINGRESP\" packet The MQTT Broker responds to the \"PINGREQ\" packet with the \"PINGRESP\" packet and thus signals its availability to the MQTT Client. Note This application example assumes an active Keep-Alive function. The Keep-Alive interval must be greater than two seconds. Table 3-18 shows the structure of the \"fixed header\" of the \"PINGRESP\" packet. Table 3-18 Fixed header Bit 7 6 5 4 3 2 1 0 Byte 1 Identifier number for MQTT control packet type = 13 (dec) Reserve 1 1 0 1 0 0 0 0 Byte 2 Remaining length: The number of following bytes after the \"fixed header\" = 0 bytes. The \"PINGRESP\" packet has no \"variable header\" and no \"payload\". 3 Useful Information LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 51 © Siemens AG 2021 All rights reserved 3.1.9 MQTT Disconnection An MQTT Client can close the connection to an MQTT Broker by sending a \"DISCONNECT\" packet to the MQTT Broker. After the MQTT Client has sent the \"DISCONNECT\" packet and closed the connection, it does not need to send any more MQTT control packets. When the MQTT Broker receives a \"DISCONNECT\" packet, it deletes all \"last will and testament\" information. As the MQTT Client is actively and voluntarily connected, the MQTT Broker does not send its last wishes to the registered subscribers. \"DISCONNECT\" packet Table 3-19 shows the structure of the \"fixed header\" of the \"DISCONNECT\" packet. Table 3-19 Fixed header Bit 7 6 5 4 3 2 1 0 Byte 1 Identifier number for MQTT control packet type = 14 (dec) Reserve 1 1 1 0 0 0 0 0 Byte 2 Remaining length: The number of following bytes after the \"fixed header\" = 0 bytes. The \"DISCONNECT\" packet has no \"variable header\" and no \"payload\". 3 Useful Information LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 52 © Siemens AG 2021 All rights reserved 3.2 How the FB \"LMQTT_Client\" Works 3.2.1 Requirements and Implementation The following requirements must be fulfilled for a communication relation between an MQTT Client and an MQTT Broker: 1. The TCP connection to the MQTT Broker is successfully established (Output \"status\" = 16#7003 \"STATUS_MQTT_CONNECTING\"). 2. The function block \"LMQTT_Client\" has logged into the broker as the MQTT Client via the existing TCP connection and established a connection (Output \"status\" = 16#7004 \"STATUS_MQTT_CONNECTED\"). 3. The trigger to send the message or to receive the MQTT connection (\"Keep- Alive\") is active. Depending on the desired quality assurance, the message is sent to the broker via the existing MQTT connection. Note An MQTT connection setup is only possible if the TCP connection to the MQTT Broker is successfully established and then maintained. An MQTT message or Keep-Alive can only be sent if there is a TCP and MQTT connection to the MQTT Broker. Overview To fulfill the mentioned requirements, several state machines were realized in the program: • State machine \"STATE_MACHINE_FUNCTION_BLOCK_TCP\": Management of the TCP connection • State machine \"MQTT_STATE_MACHINE\": Management of the MQTT connection, the sending and receiving process • State machine \"MQTT_COMMANDS\": MQTT Control Package Management 3 Useful Information LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 53 © Siemens AG 2021 All rights reserved 3.2.2 State Machine \"STATE_MACHINE_FUNCION_BLOCK_TCP\" The state machine \"STATE_MACHINE_FUNCTION_BLOCK_TCP\" is started when a positive edge is detected at input parameter \"enable\". This state machine has the following functions: • It controls the structure of the TCP connection. • It monitors the existing TCP connection for connection errors (e.g., cable breakage). • It controls the breaking of the TCP and MQTT connection. • If an error has occurred or no positive edge was detected at the \"enable\" input parameter, it sets all static tags and the other state machines to a defined state. The state machine \"STATE_MACHINE_FUNCTION_BLOCK_TCP\" contains the following states: • FB_STATE_NO_PROCESSING • FB_STATE_VALIDATE_INPUT • FB_STATE_TCP_CONNECTING • FB_STATE_OPERATING_MONITOR_TCP • FB_STATE_RECONNECTING • FB_STATE_DISABLING 3 Useful Information LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 54 © Siemens AG 2021 All rights reserved The meaning of the states is listed in the following table. Table 3-20 State Description FB_STATE_ NO_PROCCESSING The state machine waits in this state until it detects a positive edge at the input parameter \"enable\". As soon as a positive edge is detected at input parameter \"enable\", the state machine is set to the state \"FB_STATE_VALIDATE_INPUT\" and the output \"valid\" is set to the value \"TRUE\". FB_STATE_ VALIDATE_INPUT In this state, all connection parameters are read in and evaluated. The FB changes to the state \"FB_STATE_TCP_CONNECTING\" without a switching condition. FB_STATE_ TCP_CONNECTING The TCP connection to the MQTT Broker is established in this state. If the TCP connection is successfully established with \"TSEND_C\", the FB changes to the state \"FB_STATE_OPERATING_MONITOR_TCP\" and the value \"16#7003\" is output to \"status\". The TCP connection remains established until it is disconnected with \"TSEND_C\". If an error occurs when establishing the connection, the status messages for the error are output at the \"status\" and \"diagnostics\" outputs, and the FB changes to the state \"FB_STATE_NO_PROCESSING\". FB_STATE_OPERATING_ MONITOR_TCP In this state, the following actions are performed: • Receive and evaluate MQTT control packet • Send MQTT control packets • The state of the TCP connection is monitored. If the TCP connection is interrupted (e.g., due to a broken cable), the FB changes to the state \"FB_STATE_RECONNECTING\". • Manage state machine \"MQTT_STATE_MACHINE\" (see section 3.2.3) FB_STATE_RECONNECTING When the TCP connection is re-established, the FB changes back to the state \"FB_STATE_OPERATING_MONITORING_TCP\". FB_STATE_DISABLING In this state, the MQTT and TCP connection is disonnected. 3 Useful Information LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 55 © Siemens AG 2021 All rights reserved 3.2.3 State Machine \"MQTT_STATE_MACHINE\" The state machine \"MQTT_STATE_MACHINE\" is started automatically when the TCP connection is established and the value \"7003\" is output to \"status\". This state machine has the following functions: • \"Handshake procedure\" for establishing the MQTT connection. • The inputs \"publish\", \"subscribe\", and \"unsubscribe\" are evaluated in order to send the MQTT control palette that matches the job. • Managing the \"MQTT_COMMANDS\" state machine. • Sending PING packet before the Keep-Alive interval expires. The state machine \"MQTT_STATE_MACHINE\" contains the following states • MQTT_CONNECT_STATE_NO_PROCESSING • MQTT_CONNECT_STATE_BUILD_PAKET • MQTT_CONNECT_STATE_SEND_PAKET_WAIT_FOR_CONNACK • MQTT_CONNECT_STATE_CONNECTED The meaning of the states is listed in the following table: Table 3-21 State Description MQTT_CONNECT_ STATE_NO_PROCESSING If the TCP connection is not established or if an error occurs, the state machine is in the \"MQTT_CONNECT_NO_PROCESSING\" state. Only when a TCP connection is established is the switching condition to the \"MQTT_CONNECT_STATE_BUILD_PAKET\" state automatically activated. MQTT_CONNECT_ STATE_BUILD_PAKET The MQTT connection to the MQTT Broker is established in this state. A \"CONNECT\" packet is assembled for this purpose and then sent to the MQTT Broker with the \"TSEND_C\" block. The state machine changes to the state \"MQTT_CONNECT_STATE_SEND_PAKET_WAIT_FOR_ CONNACK\". MQTT_CONNECT_ STATE_SEND_PAKET_ WAIT_FOR_CONNACK The MQTT Client expects a \"CONNACK\" packet from the MQTT Broker to acknowledge the \"CONNECT\" packet. When the MQTT Broker has confirmed receipt of the \"CONNECT\" packet with a \"CONNACK\" packet, the output \"status\" is set to the value \"16#7004\". The status display \"16#7004\" indicates that the MQTT connection is established. MQTT_CONNECT_ STATE_CONNECTED In this state, the following actions are performed: • A check is conducted to see whether there is a send job for one of the following MQTT control packets: – PUBLISH – SUBSCRIBE – UNSUBSCRIBE • Manage state machine \"MQTT_COMMANDS\" (see section 3.2.4) • Monitor Keep-Alive interval. If the Keep-Alive interval is about to end, the MQTT control packet \"PINGREQ\" must be sent and the Keep-Alive interval must be restarted. 3 Useful Information LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 56 © Siemens AG 2021 All rights reserved 3.2.4 State Machine \"MQTT_COMMANDS\" The state machine \"MQTT_COMMANDS\" is only processed if the state machine \"MQTT_STATE_MACHINE\" is in the state \"MQTT_CONNECT_STATE_CONNECTED\". This is because the point the state machine \"MQTT_COMMANDS\" is started from is decided here. If there is a send impulse for a MQTT message, then the send routine becomes active. After each \"publish\", \"subscribe\", or \"unsubscribe\" send job, the output \"done\" of the FB \"LMQTT_Client\" is set to the value \"True\" and the value \"16#0000\" is indicated at the \"status\" output for 1 cycle. Subsequently, the value of the output \"status\" changes to the value \"16#7004\". Only when the input \"publish\", \"subscribe\", or \"unsubscribe\" is reset to the value \"false\", is the output \"done\" of the FB \"LMQTT_Client\" also reset to the value \"false\". If the Keep-Alive time is ending soon, the PING routine starts. The state machine \"MQTT_COMMANDS\" contains the following states: • MQTT_COMMAND_NO_PROCESSING • MQTT_COMMAND_STATE_BUILD_PUBLISH • MQTT_COMMAND_STATE_SEND_PUBLISH • MQTT_COMMAND_STATE_BUILD_SUBSCRIBE • MQTT_COMMAND_STATE_SEND_SUBSCRIBE • MQTT_COMMAND_STATE_BUILD_UNSUBSCRIBE • MQTT_COMMAND_STATE_SEND_UNSUBSCRIBE • MQTT_COMMAND_STATE_SEND_PING • MQTT_COMMAND_STATE_PING_RESP 3 Useful Information LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 57 © Siemens AG 2021 All rights reserved Table 3-22 State Description MQTT_COMMAND_ NO_PROCESSING As long as there is no send trigger and the Keep- Alive interval does not expire, the state is always \"MQTT_COMMAND_NO_PROCESSING\". MQTT_COMMAND_STATE_ BUILD_PUBLISH If a positive edge is detected at the \"publish\" input in the \"MQTT_CONNECT_STATE_CONNECTED\" state, the internal state machine \"MQTT_COMMANDS\" is set to the state \"MQTT_COMMAND_STATE_BUILD_PUBLISH\". If no other send job is running, a \"PUBLISH\" packet or a \"PUBREL\" packet is assembled and then sent to the MQTT Broker with the block \"TSEND_C\". The output \"status\" is set to the value \"16#7006\" to signal that the MQTT push mechanism is running. The state machine changes to the state \"MQTT_COMMAND_STATE_SEND_PUBLISH\". MQTT_COMMAND_STATE_ SEND_PUBLISH Depending on the QoS level, the MQTT Client may expect one of the following MQTT control packets as acknowledgement of the PUBLISH packet. • QoS = 0 (dec): The send job ends here. • QoS = 1 (dec): \"PUBACK\" packet\". When the MQTT Broker has confirmed receipt of the \"PUBLISH\" packet with a \"PUBACK\" packet, the send job is finished. • QoS = 2 (dec): \"PUBREC\" packet. When the MQTT Broker has acknowledged receipt of the \"PUBLISH\" packet with a \"PUBREC\" packet, the MQTT Client sends a \"PUBREL\" packet as confirmation. The MQTT Client expects a \"PUBCOMP\" packet from the MQTT Broker to acknowledge the \"PUBREL\" packet. When the MQTT Broker has confirmed receipt of the \"PUBREL\" packet with a \"PUBCOMP\" packet, the send job is finished. When the send job is completed, the following actions are performed: • The output \"status\" is set to the value \"16#0000\" for 1 cycle before it is set again to the value \"16#7004\". The status display \"16#7004\" indicates that the MQTT connection is established and no job is active. • The output \"done\" is set to the value \"true\". Only when the input \"publish\" is reset to the value \"false\", is the output \"done\" of the FB \"LMQTT_Client\" also reset to the value \"false\". • The state machine changes to the state \"MQTT_COMMAND_STATE_NO_ PROCESSING\". 3 Useful Information LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 58 © Siemens AG 2021 All rights reserved State Description MQTT_COMMAND_STATE_ BUILD_SUBSCRIBE If a positive edge is detected at the \"subscribe\" input in the \"MQTT_CONNECT_STATE_CONNECTED\" state, the internal state machine \"MQTT_COMMANDS\" is set to the state \"MQTT_COMMAND_STATE_BUILD_SUBSCRIBE\". If no other send job is running, a \"SUBSCRIBE\" packet is assembled and then sent to the MQTT Broker with the block \"TSEND_C\". The output \"status\" is set to the value \"16#7008\" to signal that the MQTT sub-mechanism is running. The state machine changes to the state \"MQTT_COMMAND_STATE_SEND_SUBSCRIBE\". MQTT_COMMAND_STATE_ SEND_SUBSCRIBE The MQTT Client expects a \"SUBACK\" packet from the MQTT Broker to acknowledge the \"SUBSCRIBE\" packet. When the MQTT Broker has acknowledged receipt of the \"SUBSCRIBE\" packet with a \"SUBACK\" packet, the following actions are performed: • The output \"status\" is set to the value \"16#0000\" for 1 cycle before it is set again to the value \"16#7004\". The status display \"16#7004\" indicates that the MQTT connection is established and no job is active. • The output \"done\" is set to the value \"true\". Only when the input \"subscribe\" is reset to the value \"false\", is the output \"done\" of the FB \"LMQTT_Client\" also reset to the value \"false\". • The state machine changes to the state \"MQTT_COMMAND_STATE_NO_ PROCESSING\". MQTT_COMMAND_STATE_ BUILD_UNSUBSCRIBE If a positive edge is detected at the \"unsubscribe\" input in the \"MQTT_CONNECT_STATE_CONNECTED\" state, the internal state machine \"MQTT_COMMANDS\" is set to the state \"MQTT_COMMAND_STATE_BUILD_ UNSUBSCRIBE\". If no other send job is running, an \"UNSUBSCRIBE\" packet is assembled and then sent to the MQTT Broker with the block \"TSEND_C\". The output \"status\" is set to the value \"16#7010\" to signal that the MQTT sub-mechanism is running. The state machine changes to the state \"MQTT_COMMAND_STATE_SEND_ UNSUBSCRIBE\". 3 Useful Information LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 59 © Siemens AG 2021 All rights reserved State Description MQTT_COMMAND_STATE_ SEND_UNSUBSCRIBE The MQTT Client expects an \"UNSUBACK\" packet from the MQTT Broker to acknowledge the \"UNSUBSCRIBE\" packet. When the MQTT Broker has acknowledged receipt of the \"UNSUBSCRIBE\" packet with a \"UNSUBACK\" packet, the following actions are performed: • The output \"status\" is set to the value \"16#0000\" for 1 cycle before it is set again to the value \"16#7004\". The status display \"16#7004\" indicates that the MQTT connection is established and no job is active. • The output \"done\" is set to the value \"true\". Only when the input \"unsubscribe\" is reset to the value \"false\", is the output \"done\" of the FB \"LMQTT_Client\" also reset to the value \"false\". • The state machine changes to the state \"MQTT_COMMAND_STATE_NO_ PROCESSING\". MQTT_COMMAND_STATE_ SEND_PING If the Keep-Alive interval has expired in the state \"MQTT_CONNECT_STATE_CONNECTED\", the internal state machine \"MQTT_COMMANDS\" is set to the state \"MQTT_COMMAND_STATE_SEND_PING\" and the Keep-Alive interval is restarted. If no other send job is running, a \"PING\" packet is assembled and then sent to the MQTT Broker with the block \"TSEND_C\". The output \"status\" is set to the value \"16#7005\" to signal that the MQTT ping mechanism is running. The state machine changes to the state \"MQTT_COMMAND_STATE_PING_RESP\". MQTT_COMMAND_STATE_ PING_RESP The MQTT Client expects a \"PINGRESP\" packet\" from the MQTT Broker as an acknowledgement to the \"PING\" packet. When the MQTT Broker has confirmed receipt of the \"PING\" packet with a \"PINGRESP\" packet, the state machine changes to the state \"MQTT_COMMAND_STATE_NO_PROCESSING\" and the \"status\" output is again set to the value \"16#7004\". The status display \"16#7004\" indicates that the MQTT connection is established. 3 Useful Information LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 60 © Siemens AG 2021 All rights reserved 3.2.5 Function Diagram The following figure shows the diagram of the operation with the three state machines. Figure 3-2 enable enable 0 -> 1 enable 1 -> 0 enable=0 FB_STATE_ DISABLING FB_STATE_NO_ PROCESSING FB_STATE_TCP_CONNECTING FB_STATE_OPERATING_ MONITOR_TCP Connection interrupted TSEND_C.DONE TSEND_C. ERROR MQTT_STATE_MACHINE FB_STATE_RECONNECTING MQTT_CONNECT_STATE_ BUILD_CONNECT CONNACK. ERROR MQTT_CONNECT_STATE_CONNECTED MQTT_COMMAND_ STATE_SEND_PING MQTT_COMMAND_STATE_ BUILD_UNSUBSCRIBE MQTT_COMMAND_STATE_ BUILD_SUBSCRIBE Keep alive or publish or subscribe or unsubsribe KeepAlive-Timer publish=1 MQTT_COMMAND_ STATE_BUILD_PUBLISH MQTT_COMMAND_NO_PRCESSING subscribe=1 unsubscribe=1 CONNACK. SUCCESS MQTT_STATE_MACHINE MQTT_CONNECT_STATE_SEND_ PACKET_WAIT_FOR_CONNACK MQTT_CONNECT_STATE_ CONNECTED Connection has been established MQTT_COMMAND_ STATE_PING_RESP MQTT_COMMAND_ STATE_SEND_PUBLISH MQTT_COMMAND_STATE_ SEND_SUBSCRIBE MQTT_COMMAND_STATE_ SEND_UNSUBSCRIBE TSEND_C.DONE Connection has been established 4 Appendix LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 61 © Siemens AG 2021 All rights reserved 4 Appendix 4.1 Service and support Industry Online Support Do you have any questions or need assistance? Siemens Industry Online Support offers round the clock access to our entire service and support know-how and portfolio. The Industry Online Support is the central address for information about our products, solutions and services. Product information, manuals, downloads, FAQs, application examples and videos – all information is accessible with just a few mouse clicks: support.industry.siemens.com Technical Support The Technical Support of Siemens Industry provides you fast and competent support regarding all technical queries with numerous tailor-made offers – ranging from basic support to individual support contracts. Please send queries to Technical Support via Web form: support.industry.siemens.com/cs/my/src SITRAIN – Digital Industry Academy We support you with our globally available training courses for industry with practical experience, innovative learning methods and a concept that’s tailored to the customer’s specific needs. For more information on our offered trainings and courses, as well as their locations and dates, refer to our web page: siemens.com/sitrain Service offer Our range of services includes the following: • Plant data services • Spare parts services • Repair services • On-site and maintenance services • Retrofitting and modernization services • Service programs and contracts You can find detailed information on our range of services in the service catalog web page: support.industry.siemens.com/cs/sc Industry Online Support app You will receive optimum support wherever you are with the \"Siemens Industry Online Support\" app. The app is available for iOS and Android: support.industry.siemens.com/cs/ww/en/sc/2067 4 Appendix LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 62 © Siemens AG 2021 All rights reserved 4.2 Industry Mall The Siemens Industry Mall is the platform on which the entire siemens Industry product portfolio is accessible. From the selection of products to the order and the delivery tracking, the Industry Mall enables the complete purchasing processing – directly and independently of time and location: mall.industry.siemens.com 4 Appendix LMQTT_Client Entry ID: 109748872, V3.0, 03/2021 63 © Siemens AG 2021 All rights reserved 4.3 Links and literature Table 4-1 No. Subject \\1\\ Siemens Industry Online Support https://support.industry.siemens.com \\2\\ Link to the entry page of the application example https://support.industry.siemens.com/cs/ww/en/view/109748872 \\3\\ MQTT specification http://docs.oasis-open.org/mqtt/mqtt/v3.1.1/os/mqtt-v3.1.1-os.html 4.4 Change documentation Table 4-2 Version Date Change V1.0 07/2017 First version V1.1 08/2018 \"LMqttQdn\" library added. V2.0 08/2019 Subscribe mechanism added V2.1 12/2019 Update to TIA Portal V16 V3.0 03/2021 FB \"LMQTT_Client\" V3.0 integrated in libraries for communication for SIMATIC Controllers and documentation for FB \"LMQTT_Client\" V3.0 adapted","libVersion":"0.2.4","langs":""}