Method for setting up a cross-network communication connection between a first communication device (5.11) in a first communication network (2.1) and a communication application in a second communication device (5.22) in a second communication network (2.2) via a first switching unit (3.1) connected to the first communication network (2.1) and a second switching unit (3.2) connected to the second communication network (2.2), a system address number (Sx*) which is network-internal with respect to the second communication network (3.2) being assigned to the second communication device (5.22) and an application address number (Ax*) which is network-internal with respect to the second communication network (3.2) being assigned to the communication application provided in the second communication device (5.22), - in which a unique symbolic switching address number (Vx) is assigned to the second switching unit (3.2), a symbolic system address number (Sx) which is unique with respect to the first communication network (3.1) is assigned to the second communication device (5.22), and a symbolic application address number (Ax) which is unique with respect to the first communication network (3.1) is assigned to the communication application provided in the second communication device (5.22), - in which a symbolic address indicator comprising at least the symbolic switching address number (Vx), the symbolic system address number (Sx) and the symbolic application address number (Ax) is formed, - in which, starting from the first communication device (5.11), a communication connection to the second switching unit (3.2) is set up via the first switching unit (3.1) using the symbolic switching address number (Vx) and is used to at least partially transmit the symbolic address indicator to the second switching unit (3.2), - in which at least the symbolic system address number (Sx) and application address number (Ax) contained in the transmitted symbolic address indicator are determined and are compared with data records stored in the second switching unit (3.2), and the unique network-internal system address number (Sx*) and application address number (Ax*) are determined from the data records stored in the second switching unit (3.2) using the symbolic address numbers (Sx, Ax) contained in the address indicator, and - in which the communication connection to the communication application is continued via the second communication device (5.22) using the network-internal address numbers (Sx*, Ax*), - in which the symbolic address indicator of the cross-network communication connection is respectively generated in the first communication network (3.1) before the connection is set up in the first communication device (5.11), is transmitted to the first switching unit (3.1) and is stored in the first switching unit (3.1), - in which a connection request containing at least one identifier (IPx) which identifies the first communication device (5.11) is transmitted from the first communication device (5.11) to the first switching unit (3.1), and the associated symbolic address indicator is determined in the first switching unit (3.1) using the identifier (IPx) transmitted with the connection request. - in which a unique symbolic switching address number (Vx) is assigned to the second switching unit (3.2), a symbolic system address number (Sx) which is unique with respect to the first communication network (3.1) is assigned to the second communication device (5.22), and a symbolic application address number (Ax) which is unique with respect to the first communication network (3.1) is assigned to the communication application provided in the second communication device (5.22), - in which a symbolic address indicator comprising at least the symbolic switching address number (Vx), the symbolic system address number (Sx) and the symbolic application address number (Ax) is formed, - in which, starting from the first communication device (5.11), a communication connection to the second switching unit (3.2) is set up via the first switching unit (3.1) using the symbolic switching address number (Vx) and is used to at least partially transmit the symbolic address indicator to the second switching unit (3.2), - in which at least the symbolic system address number (Sx) and application address number (Ax) contained in the transmitted symbolic address indicator are determined and are compared with data records stored in the second switching unit (3.2), and the unique network-internal system address number (Sx*) and application address number (Ax*) are determined from the data records stored in the second switching unit (3.2) using the symbolic address numbers (Sx, Ax) contained in the address indicator, and - in which the communication connection to the communication application is continued via the second communication device (5.22) using the network-internal address numbers (Sx*, Ax*), - in which the symbolic address indicator of the cross-network communication connection is respectively generated in the first communication network (3.1) before the connection is set up in the first communication device (5.11), is transmitted to the first switching unit (3.1) and is stored in the first switching unit (3.1), - in which a connection request containing at least one identifier (IPx) which identifies the first communication device (5.11) is transmitted from the first communication device (5.11) to the first switching unit (3.1), and the associated symbolic address indicator is determined in the first switching unit (3.1) using the identifier (IPx) transmitted with the connection request.