What is Ethernet Encapsulation?
Like any great piece of new technology it's important to
understand what it is before one can determine how to use
it, but before we dig
into what Ethernet Encapsulation is let's start with a
possible real world scenario.
You arrive at the plant one day, check the work order and
find that the IT department wants to gather data from each
machine on the
plant floor, and they want it quick. The IT guys think
this will be easy since they dictated that Ethernet cabling
be strung through out the plant. Unfortunately all of your
existing PLCs only have serial connections.
In the not too distant past, you would have had to contemplate running new wiring to each PLC, assuming the distances weren't too far. Another option would have been to use costly radio modems. Still, you knew there had to be a better way using the plants existing Ethernet wiring.
That's where terminal servers from companies like Digi and
Comtrol come to your rescue. A terminal server is essentially
a virtual serial port. More importantly, a virtual serial
port that can sit on your existing Ethernet network.
After learning of terminal server devices, you begin to breath
a little easier. The task of connecting all of your controllers
just took a big step back into the realm of reality. You will
be able to place a terminal server next to each machine gathering
operational data directly from the serial ports of the controller,
and bring that data back to the IT guys via their Ethernet
cabling. Problem solved and you're a hero (until tomorrow).
Now that you have an idea of what type of problems can be solved
by using a terminal server device, we can explain what Ethernet
Encapsulation is and how Kepware has added this technology
to make your job easier. If you are already familiar with
terminal servers, you may also know that many of them supply
accompanying software that allows the terminal server to
appear like a serial port to your operating system. This
software can make using a terminal server very easy and wouldn't
have required Kepware to make any changes to our software,
except for one thing - timing.
Many of the devices in the industrial market have very complicated
protocols. A protocol is a specification that determines
how we talk to the device. In many cases there are also some
very tight timing requirements that must be met in order
to successfully communicate with the device. Taking these
things into consideration, the software that often accompanies
terminal server devices has not been optimized to work with
the requirements of the plant floor environment. This is
usually seen as frequent communications errors, continuous
breaks in the communications, and long delays while the supplied
software reconnects to the terminal server. All of these
problems can make your use of a terminal server less than
ideal.
Ethernet Encapsulation
Ethernet Encapsulation is the enhanced ability of KEPServerEX
serial drivers to communicate directly with terminal servers.
As described in the previous section, we could have used the
software supplied with the terminal server, but this would
not have yielded the most optimal result in terms of performance
or reliability. With this in mind, Kepware has incorporated
the functions needed to directly connect to a serial device
connected to an Ethernet based terminal server.
If you are familiar with our serial drivers, you already know
we let you select a serial port number from 1 to 100 when configuring
a channel. For drivers that support Ethernet Encapsulation
you will now find that you also have the option of selecting "Ethernet
Encapsulation" mode. The following dialog demonstrates
how this selection is presented:
Configuring the channel for Ethernet Encapsulation mode is
only half of the story. As with any Ethernet based connection
you must also specify an IP address, a port number, and the
Ethernet communications format to be used. This is done when
you add a new device to your channel.
When a new device is added to the channel, the Ethernet Encapsulation
settings will allow you to select an Ethernet IP address, an
Ethernet Port number, and the Ethernet protocol to be used.
The device dialog for Ethernet Encapsulation appears as follows:
This dialog appears on the properties of each device you add
to a channel in Ethernet Encapsulated mode. Since this dialog
appears for each device, you can have hundreds of serial devices
connected to your Ethernet network.
Important Note: When you select Ethernet Encapsulation mode
you will notice that the serial port settings such as baud
rate, data bits, and parity become greyed out. This occurs
because these settings will not be used in Ethernet Encapsulation
mode. The terminal server you are using must ,however, have its
serial port properly configured to match the requirements of
the serial device you plan to attach to the terminal server.
Visit our OPC
Server List page to determine if the driver
you need supports this feature. If you have further questions
regarding how Ethernet Encapsulation works or how you can use
it to solve your next tough communications task, please contact
us. If it sounds like Ethernet Encapsulation is your ticket
to beating your next connectivity challenge, download our free
demo version of KEPServerEX and give it a try.
Note: Ethernet Encapsulation mode has been designed and tested
using the Digi IA Series. The
features developed will also work with other terminal server
devices that support operational characteristics similar to
the products listed above. If your terminal server supports
a raw TCP mode it should work with this feature.
Configure Digi One IA or SP for Use
with Your KEPServerEX Project
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