All the new emerging QoS service architectures are motivated by the desire to improve the overall performance of IP networks. Integrated services (Intserv), differentiated services (Diffserv), MultiProtocol Label Switching (MPLS) and constraint-based routing are all technologies starting to coexist together in today's Internet to provide means for the delivery of end-to-end QoS to applications over heterogeneous networks. We propose DRUM (Diffserv and RSVP/intserv Use of MPLS), an architecture that delivers end-to-end service guarantees for both Diffserv and Intserv networks, where part of the underlying technology used for IP transport is MPLS using Diffserv-like mechanisms for QoS provision. We also show how traffic engineering can ameliorate service differentiation, and illustrate how interoperability can be achieved between DRUM and neighboring Diffserv and Intserv networks.