This work proposes a high-level architecture towards a middleware reference model for overlay networks. Such middleware enables support to large-scale advanced network services for multimedia receivers scattered around a wide-area public network, such as the Internet. The idea is to provide services that cannot practically be directly embedded in network layer, such as multicast, security, and QoS, for instance. However, in this paper we focus only on multicast service, considering both intradomain and interdomain scenarios -- the latter being practically impossible to deploy on public networks due to administrative issues. As proof of concept, we have deployed a multimedia system taking advantage of application-level multicast from middleware support. By experimental measurements, we confirm interdomain multicast functionality over four autonomous system without any native support from underlying networks.