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RuggedRouter® User Guide
Serial Protocols Applications
Character Encapsulation
Character encapsulation is used any time a stream of characters must be reliably
transported across a network.
The character streams can be created by any serial device. The baud rates supported at
either server need not be the same. If configured, the router will obey XON/XOFF
flow control from the end devices.
One of the routers is configured to listen to TCP connection requests on a specific
TCP port number. The other server is configured to connect to its peer on the listening
port number. The RuggedRouter will attempt to connect periodically if the first
attempt fails and after a connection is broken.
The RuggedRouter can be used to connect to any device supporting TCP (e.g. a host
computer’s TCP stack or a serial application on a host using port redirection
software).
RTU Polling
The following applies to a variety of RTU protocols besides ModBus RTU, including
ModBus ASCII and DNP.
The remote router communicates with host equipment through:
• native TCP connections,
• another RuggedRouter's via a serial port or
• a port redirection package which Supports TCP.
If a RuggedRouter is used at the host end, it will wait for a request from the host,
encapsulate it in a TCP message and send it to the remote side. There, the remote
RuggedRouter will forward the original request to the RTU. When the RTU replies
the RuggedRouter will forward the encapsulated reply back to the host end.
ModBus does not employ flow-control so XON/XOFF should not be configured.
The RuggedRouter maintains configurable timers to help decide replies and requests
are complete and to handle special messages such as broadcasts.
The RuggedRouter will also handle the process of line-turnaround when used with
RS485.
Broadcast RTU Polling
Broadcast polling allows a single host connected RuggedRouter to “fan-out” a polling
stream to a number of remote RTUs.
The host equipment connects via a serial port to a RuggedRouter. Up to 32 remote
RuggedRouters may connect to the host server via the network.
Initially, the remote servers will place connections to the host server. The host server
in turn is configured to accept the required number of incoming connections.
The host will sequentially poll each RTU. Each poll received by the host server is
forwarded (i.e. broadcast) to all of the remote servers. All RTUs will receive the
request and the appropriate RTU will issue a reply. The reply is returned to the host
server, where it is forwarded to the host.
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