# Data Communications

Communications between TIBCO Substation ES and the CICS region require a Substation communication area (COMMAREA) with a maximum size of 32,000 bytes or characters. This limit is imposed by CICS for COMMAREAs.

Substation ES also supports CICS Container communications. The CICS Container is technically limited to 2 GB, but a more practical number is 2 - 3 MB. Substation ES does not support more than 4 MB for any online transaction.

When Substation ES CICS Interface issues a DPL call to a user application, it passes the formatted data buffer into the COMMAREA. From there, the data buffer is transferred to the application.

When CICS Interface communicates with TIBCO Substation ES CICS resident servers, it prefixes the COMMAREA with header and control information. If the COMMAREA must be passed to a client transaction or program, the header is stripped and the COMMAREA is transferred by way of CICS LINK, XCTL or START Transaction.

Because of the direct correlation between the TDQ record and COMMAREA, the length of a bigger TDQ record cannot exceed the supported maximum length unless HVTs are used.

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