Overlay networks for peer-to-peer networks

Every distributed system must be based on some kind of logical interconnection structure, also called an overlay network, that allows its sites to exchange information. Once distributed systems become large enough, one has to deal with sites continuously entering and leaving the system, simply because sites may fail and have to be replaced by new sites or because additional resources have to be added to preserve the functionality of the system. Hence, in general, a distributed system supporting any service has to have an overlay network supporting joining, leaving, and routing between the sites, and without a scalable implementation of such a network, the field of scalable distributed systems does not really exist.