In mobile environments, packet transmission services suffer from packet losses due to e.g. inadequate received signal quality, or forced by protocols in the signaling domain of the infrastructure of a mobile communications network. To reduce the occurrence of packet losses and, hence, to improve the quality of packet transmission services, such as e.g. the Short Message Service (SMS) deployed in GSM (Global System for Mobile Communications) based mobile communications networks, a quantitative analysis of the Quality of Service (QoS) in the signaling domain is mandatory. For this reason, appropriate QoS parameters are needed. In this communication, the authors propose such QoS parameters and apply them to the SMS in GSM networks. Furthermore, a system framework for QoS monitoring, alerting and reconfiguring an SMS Center is presented. It operates near real-time and, therefore, helps to maintain a high QoS level. Selected monitoring results gathered during real world network operation are presented.