In recent years, world of communication is ruled by the Internet Protocol stack and RS232-based interfaces are generally considered obsolete. Typical SCADA device life cycle is nevertheless long enough to guarantee demand for good old serial interfaces for several years from now. Common RS232 to TCP (UDP) converters can help in some cases by creating the required number of transparent peer-to-peer connections from all remote serial ports to the corresponding (physical or virtual) ports in the data center. However such solution requires a special routing arrangement in the center, hence it is not always feasible. A typical SCADA Front End Processor (the central interface of the application to the communication network) uses a proprietary protocol over a single RS232 interface. Each message coming out from the FEP is addressed and should be delivered to the designated remote serial port. Certainly a transparent broadcasting to all remotes could do the job, making the service provider happy (assuming the resulting bills are paid). Obviously the proper solution is to transmit the message to the destination address only.
A SCADA serial protocol typically uses simple 8 or 16 bit addressing. The cellular network address scheme is an IP network, where the range is defined by the service provider (sometimes including individual addresses, even in the case of a private APN). Consequently a mechanism of translation between the SCADA and the IP addresses is required. To make things worse, IP addresses may be assigned to cellular devices dynamically upon each connection.
This chapter describes how to efficiently solve this problem using RACOM made routers.
Two basic situations are described:
The M!DGE/MG102i IP addresses are reachable from each other in both directions. This can either mean that you have the private APN with the own IP subnet for your application. Or it can mean that all routers have static public IP addresses. The example in Chapter 1, SCADA Protocols – private APN shows the routers’ configuration using the private APN with static addresses.
The M!DGE/MG102i IP addresses are NOT reachable in both directions – only the center is reachable from the remote side. The center must have a static public IP address. The remote units (slaves in the Master-Slave configuration) can have private and dynamic IP addresses. Utilization of VPN tunnels is required. See the example Chapter 2, SCADA Protocols – public APN for more details.