Motorola MOSCAD 68P02958C00-B User Manual page 28

receipt of data transmissions initiated by the field RTUs (so called burst/RTU event data,
contention data or Change-Of-State [COS] messages).
A specialized routine, API CONNECT, allows the SCADA Interface to establish the most
fitting mode of communication with the IP Gateway, based on the existing SCADA
communication mode.
Channels and Channel types
The SCADA Interface must establish at least one connection toward the IP Gateway server.
These connections are called channels and are used to transfer messages from the SCADA
center toward both the Gateway and the RTUs in the field. The client application can open
different types of channels to best serve its SCADA Interface process.
The two basic channel types are:
Regular
Spontaneous
A Regular channel enables asynchronous sending/receiving of data and requests. It uses
amailbox mechanism for mapping the request messages to their replies.
A Spontaneous channel allows receiving burst data (Spontaneous COS messages) and RTU
events - i.e. transmissions initiated by the field RTUs. This feature almost eliminates the need
for the SCADA application to poll data since every change in one of the telemetry field
variables can immediately be transmitted to the SCADA application.
MOSCAD System - RTU definitions
To make the MOSCAD field system definition transparent to the SCADA client application
and to correctly parse the data received from the MOSCAD system, the API builds an internal
data structure defining the types and numbers of the field RTUs. To do so, it uses two external
system definition files (in ASCII format).
This automatic system definition done by the API routines hides the field system structure
from the SCADA application and eliminates the need for any application modifications when
working with different MOSCAD systems. Moreover, new RTUs can be added to the system
at run time using the appropriate API routine.
Primary/Secondary Gateway Modes
The IP Gateway supports a redundant configuration. There are two modes of operation:
Primary and Secondary. The initial mode of operation is defined by the startup process of the
IP Gateway. At any other time, the SCADA can change the mode of operation flexibly by
calling the appropriate API set mode routine. The API also supplies a routine for checking the
current mode of operation. This functionality of the IP Gateway provides redundant gateway
operation, which minimizes the risk of communication failure.
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System Overview