Abstract. MPNT (Multicast Proxies NeTwork) is an overlay architecture that was first conceived to provide multicast access to unicast-only users, like TutTelNet distant students. MPNT has been then improved by implementing multimedia access (mainly RTP, RTCP and SIP). MPNT original topology is spanning tree based. It is the most efficient topology in terms of switching delay (no routing) but the global delay variance can be important. To remedy this, we implemented an alternate hypercubebased topology. Indeed, hypercubes have several interesting properties - mainly compactness - that ensure a better scalability. Nevertheless, this logical hypercube optimization is valid provided that interconnecting links are comparable. To adapt the architecture to the network heterogeneity, we implemented thus a hybrid topology exploiting both spanning tree and hypercube advantages.