Communication system for the communication in a communication network, wherein the communication network has a first sub-network and a second sub-network, with: a first identifying entity, which is assigned to the first sub-network and designed to receive an identity of a communication terminal, and to identify the communication terminal for communicating via the first sub-network on the basis of the identity; a second identifying entity, which is assigned to the second sub-network and designed to receive the identity of the communication terminal, and to identify the communication terminal for communicating over the second sub-network on the basis of the identity; and a management entity, which is designed to authenticate the communication terminal for communication over the respective sub-network (307, 311), wherein the management entity is designed to authenticate the communication terminal on the basis of an assignment of sub-networks (307, 311, 315) to identities of communication terminals, and wherein the management entity is designed to authenticate the communication terminal for communication over the first sub-network if the first sub-network is assigned to the identity of the communication terminal, or to authenticate the communication terminal for communication over the second sub-network if the second sub-network is assigned to the identity of the communication terminal, characterized in that when contact is made with the first identifying entity by the communication terminal, the management entity is designed to transmit a sub-network code of the second identifying entity to the communication terminal over the first identifying entity if the communication terminal is authenticated for communication over the second sub-network, or when contact is made with the second identifying entity by the communication terminal, the management entity is designed to transmit a sub-network code of the first identifying entity to the communication terminal over the second identifying entity if the communication terminal is authenticated for communication over the first sub-network. a first identifying entity, which is assigned to the first sub-network and designed to receive an identity of a communication terminal, and to identify the communication terminal for communicating via the first sub-network on the basis of the identity; a second identifying entity, which is assigned to the second sub-network and designed to receive the identity of the communication terminal, and to identify the communication terminal for communicating over the second sub-network on the basis of the identity; and a management entity, which is designed to authenticate the communication terminal for communication over the respective sub-network (307, 311), wherein the management entity is designed to authenticate the communication terminal on the basis of an assignment of sub-networks (307, 311, 315) to identities of communication terminals, and wherein the management entity is designed to authenticate the communication terminal for communication over the first sub-network if the first sub-network is assigned to the identity of the communication terminal, or to authenticate the communication terminal for communication over the second sub-network if the second sub-network is assigned to the identity of the communication terminal, characterized in that when contact is made with the first identifying entity by the communication terminal, the management entity is designed to transmit a sub-network code of the second identifying entity to the communication terminal over the first identifying entity if the communication terminal is authenticated for communication over the second sub-network, or when contact is made with the second identifying entity by the communication terminal, the management entity is designed to transmit a sub-network code of the first identifying entity to the communication terminal over the second identifying entity if the communication terminal is authenticated for communication over the first sub-network.