Functional Groups, often referred to as the “inner envelope,” are made up of one or more Transaction Sets. One Functional Group Envelope must include transaction of all of the same type, which can be batched together into one transmission. The Functional Group is defined by the header and trailer segments.
The Functional Group Header (designated GS) segment appears at the beginning, and the Functional Group Trailer (designated GE) segment appears at the end. Many Transaction Sets of the same type can be included in the Functional Group.
Within the Functional Group, each Transaction Set is assigned a functional identifier code, which is the first data element of the header segment. The Transaction Sets that constitute a specific Functional Group are identified by this functional ID code.