Understanding Servers, Converters and Gateways

Emerson's Craig Abbott

As instrumentation and control system, also known as Operational Technology (OT) incorporate wireless and other classic Informational Technology (IT) components, the worlds of OT and IT continue to merge.

For control and automation specialists, it means things like servers, converters and gateways become part of the learning path.

Emerson’s Craig Abbott had a great LinkedIn post, Servers, Converters and Gateways! Oh My!, which I somehow missed when he published it last summer (or winter from his vantage in Australia). I’ll excerpt a few of his thoughts and invite you to read the full post.

Rosemount 1410 / 1420 WirelessHART Gateway

It is important to understand that the gateways do not simply translate the messages. For the most part, WirelessHART data from the field is stored in the gateway and data requests are performed on the stored data. Read requests are not passed through to the field. In the case of a write, the write is applied to the internal data and then an update is sent to the field as a WirelessHART message. HART/IP is the exception here as HART messages need to be sent to the transmitters. All HART messages are converted into WirelessHART equivalents and passed through to the field with responses converted back to HART/IP and passed back to the requestor.

With the Gateway in place, there is no WirelessHART on your IT network, and no Modbus, Ethernet/IP or OPC on your wireless field network. Data requests seem to be converted from the Ethernet Media to the Wireless Media, but they are not, and at a protocol level, there is a lot more management and protocol translation going on.

A Terminal Server is completely at the other end of the scale. Terminal Servers are pure media converters with little or no message management. A Terminal Server captures data arriving at the serial port, wraps it up into an Ethernet packet and delivers the data to a remote location untouched. That last single word is important – untouched. The Terminal Server does no conversion nor translation, it simply delivers data in its raw form. When two Terminal Servers are linked to each other across a network, in what is termed a “Back to Back” configuration, serial data arriving at one end will pop out of the other, and vice versa. Serial cables have a limit of only a few metres in length and are subject to interference in the form of electrical noise. Carrying the data packets over network cables can remove these limitations.

Terminal Servers for Network Transport

Read Craig’s full post for more on the role of Device Servers, serial protocols and how he and his team solved a challenge connecting Ethernet to a serial protocol. The worlds of OT and IT continue to grow ever closer.

You can connect and interact with other networking experts in the Wireless and SCADA groups in the Emerson Exchange 365 community.

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