For some use cases I'd think an IGMP-like protocol would be best. Specifically for pub/sub, where a URI might denote/resolve to one or more group membership management services, where publishers, routers, and subscribers join as such and where the topology is worked out dynamically (this is easy enough for publishers and subscribers, but a bit harder for routers as real topology information would be nice to have but possibly difficult to extract from the network). Nico --