# Communication Fields

Communication fields are named fields within a user message that assist in bidirectional Substation ES communication. These fields enhance the ability of an application to effectively forward additional information and receive notifications when conversing with Substation ES.

## Categories

Substation ES communication fields are divided into the following categories:

- Substation ES system fields, which are defined in a user message and are used by applications and Substation ES during communication. System fields can be bidirectional. System fields are not stored within the Substation ES communication buffer passed to a BES application. Therefore, Substation ES processes these fields differently than normal message fields.
- Substation ES user fields, which are part of the Application Notification and are Substation ES output-only fields. These fields enable applications to identify information regarding the application’s communication with Substation ES.

All communication field names consist of a variable prefix and a suffix constant. The prefix length is a maximum of 51 characters.

## Prefix

All Substation ES communication fields use a default prefix of tibss-. When explicitly referenced, the prefix together with the name must be specified either in Substation configuration UI or by applications communicating with Substation, such as TIBCO ActiveMatrix BusinessWorks processes or network programs.

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