T H E M O D E R N M - B U S T E C H N O L O G Y
PiiGAB Process Information i Göteborg AB
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8.1.2
Non-Redirected Connection vs. Redirected Connections
Most software applications that need to use the Com Port Redirector have been
designed to connect directly to the serial device being managed. This connection is
achieved using a direct cable connection from a com port on the personal
computer (PC) running the software utility to the serial port of the serial device
being managed. With this configuration, the PC and the managed serial device
reside on an isolated serial network. The traffic passed on the physical media
between them is intended for either PC or the serial device. Latency is not an issue
in this scenario.
When the same software applications are used with the Com Port Redirector, the
applications are no longer directly attached to the serial device being managed.
Instead, all traffic between the software application and the serial device is routed
as follows:
1.
From a virtual com port, the data is stripped out of a serial packet and
placed into an IP packet.
2.
The serial packet is sent from the virtual com port to a network interface
on the PC.
3.
Data is transmitted over the network, through switches or routers, to the
network interface on a device server.
4.
From the network interface on the device server, the data converts from
an IP packet back to a serial packet.
5.
Once in a serial packet, data is transmitted down the physical media to the
serial device.
This process introduces latency. The amount of latency associated with this type of
connection is determined by the amount of network latency. The more traffic on
the network, the greater the latency between the PC running the software
application and the M-Bus gateway.
To address latency, Com Port Redirector provides a
No Net Close
option in the
Port Settings dialog box. This option keeps the TCP/IP connection open when the
com port is closed, reducing latency.
