The Closed User Group (CUG) or the closed user group (GBG) describes the feature of a dial-up or radio network that only allows bilateral communication relationships between certain pairs of connections. This feature provides the ability to communicate only within a predetermined group of subscribers.
In addition, the traffic relationships between the subscribers in the group and their permissions to each other can be specified. The closed user group makes it possible to set up closed company networks with the highest security requirements. Participants who do not belong to the closed user group cannot connect to participants of the group. The groups usually have limited communication possibilities, which mostly takes place within the group. In addition, the traffic relationships between the participants of the group and their authorizations among themselves can be defined. In terms of application, it is a defined user group of a data network or service that is characterized by the same information needs or functionalities.
In addition to the application-related meaning, the term closed user group also has a technical meaning. In the technical interpretation, it is a group of specific ports, each of which can connect to another port within the same group. The ports of a closed user group are not accessible from any port outside the group.