In this paper, we propose and analyze a new system architecture for video multicast over Internet, namely, the sender-adaptive and receiver-driven layered multicast (SARLM). In SARLM, the sender of a video source splits the video data coded by a scalable codec and a channel codec into multiple data streams, each of which corresponds to a separate multicast group. The sender can adjust the way in which the video sequence is split dynamically based on the receivers' network parameters collected through feedback. Meanwhile, a receiver can estimate available bandwidth based on a modified packet-pair technique and choose to reassemble and playback the video sequence for a given quality level by dynamically subscribing a given part or all of the data streams according to its network conditions. To optimize the sender's adaptation strategy, we introduce a quality-space (Q-Space) model to describe and analyze the mathematical relationship between the sending rate of different. SARLM layers and the video quality received by a given receiver identified by its network characteristics including available bandwidth and packet loss ratio. Our simulation results demonstrate that, under the same network topology and condition, the SARLM architecture can achieve higher network throughput and better video qualities on the receiver side than the existing approaches.