Lookup services organize the services they contain into groups. A group is simply a set of registered services identified by a string. This kind of redundancy can help make the Jini technology system more fault tolerant. The runtime infrastructure enables services to register with lookup services through a process called discovery and join . Discovery is the process by which a Jini technology-enabled device locates lookup services on the network and obtains references to them.
Join is the process by which a device registers the services it offers with lookup services.
Lookup services monitor the well-known port for presence announcement packets. When a lookup service receives a presence announcement, it inspects the list of group names contained in the packet. Once a device has discovered a lookup service, it can register its own services on that lookup service via the join process. The join process begins when a service connects to a lookup service via the object it received from that lookup service during the discovery process. Through the stub, the service sends information about itself to the lookup service.