Motorola 68P02958C00-B - Manual (Page 115)

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Network Configuration
The Network Configuration program is used for defining the communication nodes
(interconnection points between two or more links) in the network. The program defines the
network’s structure; there is no need to define all RTUs, only the nodes in the network. The
communication protocol uses these definitions for automatic routing of the packets through the
network.
In simple networks, such as one IP Gateway connected to one communication link, it is not
necessary to use this program (see Communication Network in the MOSCAD Programming
ToolBox System Overview manual).
The RTU and IP Gateway ports defined as Computer port, which serve as connection to the
ToolBox or centrals, are not considered as links in the network but as local ports.
A network configuration is stored in a file. The network configuration can be loaded into the
RTU or IP Gateway together with the application. During application loading, the user is
asked to provide the name of the network configuration file.
The same network configuration file is used for all the sites in the system and also may be
used in other networks that have the same structure. The network configuration must be
loaded to all sites in the system to enable each site to route the packets through the network.
When additional sites are to be added to the network, it is not necessary to change the network
configuration definitions since Network Configuration defines only the nodes in the network.
All you have to do is to define the main communication port of each site, via Site
Configuration, and to connect it to one of the network links, using the logical (symbolic) name
of the link.
Routing of Data Frames
The network configuration serves as an internal data bank which describes a path to each link
in the network. When data frames are to be relayed to another site, the node checks if it has a
direct link to the destination. If so, the data is transmitted. If there is no direct link, or if that
link is in “fail” state, the unit will use the network map to try to identify another path.
A device called “NSTOCK” (a Software Diagnostics Level 2 device) provides the full list of
data links (as defined in Network Configuration), and adds the status during runtime. The
transmitting node will try each path (sequentially, starting with the first entry) until it is
successful. If some of the links are in “fail” state, the node will try the first link that is in
working order. If all possible links are in “fail” state, it will try the first path. If the
transmission fails, the frame is discarded.
When a data link fails to acknowledge transmission, it is marked as “fail” in the network data
bank. The failed link can be restored to “OK” status if another transmission happens to
succeed. Another mechanism exists, whereby the network performs periodic checks on failed
links and restores them to “OK” status is an acknowledgement is received. When this