====== Communication between 2 or more WebHMIs via internet ======

Sometimes you need to have a connection between far systems, e.g. like in the following picture:

{{ network:two_webhmi_over_l2.png?direct&600 |}}

You might want to automatically control supply pumps depending on the water level in a far water tower or reservoir. 

With the WebHMI and Level2 connectivity options it is done with ease:

==== Option 1. Using MQTT protocol ====

  - Connect both WebHMIs to the Level2 IoT 
  - Subscribe the pump station WebHMI to the topic with level that far WebhMI publish onto the Level2 MQTT broker.

==== Option 2. VPN and Modbus TCP ===== 

  -[[level2:how_to_connect_webhmi_to_level2|Connect both WebHMIs to Level2]] and and remember remote node (reservoir side) IP address in the VPN network  
  -Turn On ([[:modbus_tcp_server|Modbus TCP Server]]) on the water redervoir side 
  -Enable [[:remote_service_access|routing]] for pump side WebHMI to the remote peer node 
  -Create Modbus TCP connection on the pump side WebHMI using IP address from (1)


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__Option 1__ Is preffered due to the nature of the MQTT protcol which saves traffice for communication while Modbus TCP will create constant polling process. 
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