A network gateway device for real time communication connections based on a packet-oriented transport protocol between a first communication network with a first connection control protocol set on the transport protocol and with a second communication network with a second connection control protocol set on the transport protocol, with a) a first and a second data interface based on a transport protocol for coupling the first and the second communication network logically directly on the plane of the transport protocol, b) a first signaling interface based on the first connection control protocol and coupled to the first data interface and with a second signaling interface based on the second connection control protocol and coupled to the second data interface, c) a conversion device (SIWU) coupled to the first and the second signaling interface for converting between the first and the second connection control protocol, and d) a proxy device (PROXY) for representing a service feature supported in the first communication network and not represented in the second communication network to the first communication network and to the logical termination of a service feature signal if the service feature concerned is not supported in the second communication network, e) wherein the first connection control protocol is realized by a protocol according to the ITU-T recommendation H. 323 and the second connection control protocol is realized by an SIP protocol (Session Initiation Protocol) of the IETF forum, or wherein the first connection control protocol is realized by the SIP protocol of the IETF forum and the second connection control protocol is realized by the protocol according to the ITU recommendation H.323, characterized by a service quality control for converting service quality classes of the connection control protocols to transport protocol-specific service quality classes. a) a first and a second data interface based on a transport protocol for coupling the first and the second communication network logically directly on the plane of the transport protocol, b) a first signaling interface based on the first connection control protocol and coupled to the first data interface and with a second signaling interface based on the second connection control protocol and coupled to the second data interface, c) a conversion device (SIWU) coupled to the first and the second signaling interface for converting between the first and the second connection control protocol, and d) a proxy device (PROXY) for representing a service feature supported in the first communication network and not represented in the second communication network to the first communication network and to the logical termination of a service feature signal if the service feature concerned is not supported in the second communication network, e) wherein the first connection control protocol is realized by a protocol according to the ITU-T recommendation H. 323 and the second connection control protocol is realized by an SIP protocol (Session Initiation Protocol) of the IETF forum, or wherein the first connection control protocol is realized by the SIP protocol of the IETF forum and the second connection control protocol is realized by the protocol according to the ITU recommendation H.323, characterized by a service quality control for converting service quality classes of the connection control protocols to transport protocol-specific service quality classes.