It seems logical they should use a lookup service to access the lookup services. The answer lies in the discovery protocol, arguably one of the most important Jini protocols. Through discovery, devices and components can find the lookup services available on the network. Once a device or a component has discovered lookup services, it can register its own services or join services. To join a lookup service, the device or application sends information about itself and the services it supports.
Discovery is a boostrap protocol, a protocol that helps get started.
There are many different network organizations. Multicast Request Multicast allows devices and components to advertise their presence on a local area network. On startup, devices and components send several multicast UDP packets to a well-known port. By definition, multicast packets are received by every station on the local-area network therefore if there is a lookup service somewhere on the network, it will hear about the device. See Figure 1 for an illustration of a multicast request.