QoS-aware multicasting is becoming more and more desirable with the expanding usage of group-based applications, especially those involving multimedia objects. Until now, most of the proposed QoS-aware multicasting routing protocols adopt per-flow based resource reservation. Although these schemes can be adopted in integrated services (IntServ) Internet, they are not suitable for more scalable Differentiated Services (DiffServ) Internet. A new QoS-aware multicast routing protocol called QMD is proposed for DiffServ environments in this paper. Based on the design philosophy of DiffServ, the complex multicasting control plane functionalities are removed from the core routers. In addition, for each multicast group, only a limited set of on-tree routers (termed as key nodes) maintain multicast routing states and forward multicast data traffic. The key nodes of a multicast group uniquely identify a QoS-satisfied multicast tree connecting the group members. Although the other on-tree routers between any two key nodes do not maintain any multicast routing states and QoS reservation information, the group members' QoS requirements can still be satisfied. Through simulation experiments based on both random and real intra-domain topologies, we have also demonstrated that QMD can provide higher QoS-satisfaction rate while maintaining the simplicity of core routers.
