An IP gateway, attached to a source network and a destination network, handles an application session between a source client device and a destination client device. Application-level control messages in the existing application session may be time stamped by the IP gateway. Individual network round-trip delays (RTDs) associated with the attached networks may be calculated or determined utilizing the resulting time stamps. The IP gateway may time stamp one or more of the application-level control messages in the existing application session whenever transmission and/or reception of the application-level control messages occurs at the IP gateway. The resulting gateway related time stamps such as the gateway-to-source receive time stamp and the gateway-to-destination transmit time stamp may be stored. An individual RTD associated with the destination network may be calculated or determined utilizing the stored gateway related time stamps and processing delay measurement extracted from one of the application-level control messages from the destination client device.