M!DGE3 in detail

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5. M!DGE3 in detail

5.1. Combination of IP and serial communication

M!DGE3 enables combination of IP and serial protocols within a single application.

Five independent terminal servers are available in M!DGE3. Terminal server is a virtual substitute for devices used as serial-to-TCP(UDP) converters. It encapsulates serial protocol to TCP(UDP) and vice versa eliminating the transfer of TCP overhead over the radio channel.

If the data structure of a packet is identical for IP and serial protocols, the terminal server can serve as a converter between TCP(UDP)/IP and serial protocols (RS232, RS485).

You can see an instructional video explaining the Terminal server functionality here: https://www.racom.eu/ripex-terminal

5.1.1. Detailed Description

Generally, a Terminal server (also referred to as Serial server) enables connection of devices with a serial interface to a M!DGE3 over the local area network (LAN). It is a virtual substitute for the devices used as serial-to-TCP(UDP) converters.

Examples of the use:

A SCADA application in the center should be connected to the radio network via serial interface, however, for some reason that serial interface is not used. The operating system (e.g. Windows) can provide a virtual serial interface to such application and converts the serial data to TCP (UDP) datagrams, which are then received by the terminal server in M!DGE3. This type of connection between M!DGE3 SCADA and application is beneficial in the following circumstances:

  • There is no hardware serial interface on the computer

  • Serial cable between M!DGE3 and computer would be too long. E.g. the M!DGE3 is installed very close to the antenna to reduce feed line loss.

  • LAN already exists between the computer and the point of installation

In special cases, the Terminal server can reduce network load from TCP applications. A TCP session can be terminated locally at the Terminal server in M!DGE3. User data are extracted from the TCP messages and processed as if it came from a COM port. When the data reaches the destination M!DGE3, it can be transferred to the RTU either via the serial interface or via TCP (UDP), using the Terminal server again. Please note, that M!DGE3 Terminal server implementation also supports the dynamical IP port change in every incoming application datagram. In such a case the M!DGE3 sends the reply to the port from which the last response has been received. This feature allows to extend the number of simultaneously opened TCP connections between the M!DGE3 and the locally connected application up to 10 on each Terminal server.