SCADA Protocols over Frame Relay -
Supporting Modbus, DNP, and others without configuration?

The DCB Broadcast Polling FRAD is the only FRAD specifically marketed for the SCADA wide area network. It was designed to handle multiple SCADA protocols with no protocol specific configuration.

This FRAD was developed from proven DCB products which have been in use for over a decade in the information technology world of host mainframe computers and remote terminals. Since the hardware was optimized for asynchronous port devices and a synchronous network connection, it was relatively easy to evolve it into an asynchronous FRAD with firmware designed to handle the unique characteristics of SCADA networking.

Our customers asked us for a way to build a bridge between yesterday's installed base of RTUs and tomorrows fancy feature-rich equipment. By making a decree that all new wide are networks will be based upon frame relay or ethernet, they set the course for modernization that will take them into the future. But, they also have installed plant that still has decades of useful life. Economic realities dictate that this installed equipment must be moved onto the new network technology with a minimum of new investment. Since the network of choice for legacy SCADA systems is the multi-drop analog modem line, we designed replacements for that technology. For frame relay networks, we built the Broadcast Polling Frad (BPF) to be a drop-in replacement for multi-drop modems. For Ethernet networks, we introduced the EtherPoll, SCADA serial server as a similar drop-in modem replacement.

Although running on different types of networks, both of these have a few things in common. They both support most any byte oriented SCADA protocol. We do this by having configurable dynamic block sizes, inactivity timers, control lead transitions that suit SCADA equipment, and proprietary mechanisms that maintain datagram integrity. The most common protocols in use today, Modbus ASCII, Modbus RTU, and DNP all fit this model quite well, as do numerous proprietary and home-grown byte-oriented asynchronous protocols.

Special versions of these products also support non-byte oriented protocols such as Conitel and Racal-Redac. The unique method used with these protocols allow transport via byte-oriented networks as well as synchronous networks.

Since our network interface devices take care of the SCADA protocol transparently, running multiple protocol networks over the same network transport is easy. The economic benefit is tremendous. Adding a new protocol or SCADA system on an existing network by using two-port devices is much more cost-effective than adding a totally separate network.

Products to check out:
The EtherPoll, an ethernet SCADA communications server. Datasheet is here. The manual is here.

The Broadcast Polling Frad (BPF) is a frame relay FRAD designed for SCADA. The Data sheet is here. The manual is here.

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