This paper describes an approach to detect Quality of Service degradation due to packet congestion within wireless networks. The proposed approach can assist management systems to detect a degradation based on easy determinable packet metrics. Metrics like interface queue length, round trip times and retry ratio are evaluated regarding thresholds and detection performance. With a combination of metrics, a robust detection can be achieved for TCP and UDP streams using a IEEE 802.11 a/b/g ad-hoc network. As soon as a detection event occurs, a channel transition is engaged as an exemplary counter-measure. This successfully solves transmission problems due to congestion.