System Data Interface (Sdi) Protocol - GE Mark VIe System Manual

4.5 System Data Interface (SDI) Protocol

The SDI protocol is a configuration protocol layered upon TCP/IP. SDI is used primarily between the ToolboxST application
and the other control system devices on the UDH (controllers, HMIs, and Historians). SDI commands support configuration
downloads, file transfers, debugging, live data access, and a variety of other activities. The SDI connection between the
ToolboxST application and the controllers is secured when the SecurityST server is deployed. SDI is also used by the
WorkstationST application to monitor controller status, upload trip logs, transport alarms from the devices to the
WorkstationST Alarm Server, and to transmit alarm commands to the controllers.
Note The Mark VIe control systems can support up to a maximum of 10 supervisory PCs with individual alarm server
connections to a unit controller (not including OSM and Historian).
The total number of SDI connections to any particular controller must be limited to prevent overburdening controller
resources, so attention must be paid to the overall system architecture during the application engineering design phase. For
example, supporting a large number of WorkstationST Alarm Viewers is best accomplished by deploying a centralized alarm
server with a single SDI connection to the controller rather than having each HMI run its own alarm server and therefore a
separate SDI connection from the controller to each HMI. In addition, sites with multiple HMIs should limit requests for
controller trip logs to be made from only a few HMIs as to not overburden the Mark VIe controller.
Because EGD does not create a connection per HMI, EGD is typically used for live data transfer and to fan data out from
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controllers to a large number of HMIs. SDI is used for live data in cases such as ExperTune support, where a large number
of variables must be made available but only a few variables will be accessed at any one time.
An SDI server runs on the Mark VIe controller to provides a communication mechanism between the controller and the HMI.
The server on the controller waits for the ToolboxST and WorkstationST applications to establish connections. It allows the
HMI to retrieve data from the controller and for the ToolboxST and WorkstationST applications to run commands in the
controller.
SDI is a communication scheme that is built on top of TCP/IP, which provides a reliable delivery mechanism between two
communicating parties. Data that is sent from one to the other is guaranteed to be delivered, and delivered in the correct order.
When a segment of data is sent by TCP/IP, the sender will wait for an acknowledgement of the segment. If the
acknowledgment is not received, the data will be resent. Also, if data is not delivered in the correct order, TCP/IP will
reorganize it in the correct order. TCP/IP will also discard any duplicate packets.
Communication Protocols GEH-6721_Vol_I_BP System Guide 111
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