Degradation of network performance during video transmission may lead to disturbing visual artifacts. Some packets might be lost, corrupted or delayed, making it impossible to properly decode the video data on time at the receiver. The quality of the error-concealment technique, as well as the spatial and temporal position of the artifacts have a large impact on the perceived quality after decoding. In this paper, we use the spatial scalability feature of Scalable Video Coding (SVC) for error-concealment. This enables the transmission of a lower resolution video with a higher robustness, for example using unequal error protection. Under the assumption that only the higher resolution video would be affected, we evaluated the visual impact of packet losses in a large scale subjective video quality experiment using the Absolute Category Rating method. The number of impairments, the duration, and the interval between impairments as well the quality of the encoded lower resolution video are varied in a systematic evaluation. This allows for analyzing the influence of each factor both independently and jointly.