The Group object (a collection of objects on the same device) and the GlobalGroup object (a collection across multiple devices) allow several objects to be operated on in a single BACnet transaction, optimising polling and batch commands.

A Group object holds a list of object references on the local Device, whereas a GlobalGroup references objects across several Devices on a single BACnet internetwork. In both cases Present_Value is an array of the current values, so a single ReadProperty targeting the Group returns all members at once. This collapses, for example, 50 separate ReadProperty transactions into one and is configured during commissioning: define the members once and benefit from simplified access thereafter.

Watch the APDU size when populating a GlobalGroup: too many members can push the response past Max_APDU_Length_Accepted and force segmentation, which negates the bandwidth saving you were aiming for.