|
In industrial
communication applications, this functionality is often referred to by
brand name products such as Pyramid Integrator or BridgeMUX.
In fact, the proper technical term for this type of equipment is
router where messages from one network are passed-through to another
network. This functionality is
sometimes confused with that of a protocol converter, which only
incidentally bridges different networks, and is primarily concerned with
parsing messages from incompatible network protocols and relaying it in
the native protocol of the requesting device or system.
Routers completely ignore protocol and instead relay the entire
message (unparsed) from one network to another..
When all devices
along a communication path are protocol compatible, a router functionality
is preferred for its simplicity and flexibility.
Unlike protocol
conversion, individual data points do not require mapping between source
and destination. Instead, each
network node has its address recorded within the configuration file so
that requests are identified and redirected to the appropriate network and
responded to by the remote device.
This not only
makes configuration very simple, since only the station and not the
individual data points are mapped, but provides complete flexibility in
addressing the unprotected memory of a remote device.
 Open
Access vs Firewall
One of the
implications for use of routers over protocol converters is that a master
on one network can have unrestricted access to the unprotected memory of
all mapped devices on another network.
Changes in which data is being requested only need to be made at
the master.
This is sometimes
undesirable, especially in custody-transfer applications.
Using the protocol converter mode of the Liaison communication
processors only allows requests where the data is “mapped”, creating
an effective firewall since any unmapped request is simply ignored.
Applications
Router mode is a
usable option where all connected networks share the same application
layer such as Modbus Plus, Modbus RTU and Modicon TCP/IP.
Even though all of these networks use different media (custom
RS-485, serial and Ethernet), they all share the same addressing structure
and function codes. This
allows a Modbus message to be passed from Ethernet to serial and back
again. As of this writing, the
Modicon driver set has been enabled for use with Liaison communication
processor router mode functionality. Prospectively,
router mode will be enabled for Allen-Bradley protocols (CSP Ethernet,
DF-1, Data Highway Plus), the GE family of protocols and others.
Features
-
Multi-channel
capabilities: Liaison communication processors feature multi-channel
communication capabilities. Users can implement multiple ports
of a single media type (i.e. multiple serial ports--Modbus RTU, Modbus
ASCII), bridge to Ethernet or Modbus Plus, or create a single virtual
network using all three media types.
-
Redundancy:
Liaison communication processors have remarkable flexibility for
implementing redundant networks, even in router applications.
Dual Ethernet, Redundant Modbus Plus buses and serial Modbus
channels require no special options or settings.
-
Flexible
Hardware Configurations: Serial ports
(either RS-232 or RS-485) can be implemented in almost any number, from
one to 4, 8, 16, up to 128 ports.
Available with RS-232/422 and 485 serial ports featuring surge
suppression and optional optical isolation. Contact
Liaison or your local authorized representative for a recommended hardware
configuration.
-
Extensive
Remote Monitoring, Configuration and Diagnostic Capabilities:
Using either the standard built-in
Ethernet port or a serial port, all configuration, monitoring and
diagnostic data is available through telnet or your web browser.
Add stations and get diagnostic information over a modem, network or
by direct connection to a serial or Ethernet port.
...or
call (888) 641-6108
|
|
PDF version for download