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JXTA in a Nutshell by Li Gong, Bernard Traversat, Scott Oaks

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Discovery

So far, our shell does not know a lot of peers. In the JXTA world, this is not a good thing, as a peerless JXTA application is not very useful. The first thing it must do, therefore, is find other peers with whom it can exchange information. The process of finding other peers is called discovery.

The process of discovery applies to any JXTA resource: peers discover other peers, and they also discover peergroups, pipes, advertisements, and other resources. There are two ways in which peers discover resources: peers discover resources dynamically, and they use special, statically configured peers to tell them about JXTA resources. Discovery occurs within the context of a peergroup: a peer attempts to discover resources within a specific peergroup.

Dynamic Discovery

Peers use the JXTA Peer Discovery Protocol (PDP) to discover JXTA resources dynamically. The PDP defines the lowest-level technique that is available for peers to discover resources. On an IP network, it consists of two parts: a multicast message that is sent on the local network and the use of rendezvous peers to discover peers beyond the scope of the local network. Other network bindings will behave differently, but the essential operation of the PDP is that the requesting peer sends a message, and resources that hear the request will respond directly to the peer. Therefore, a peer using PDP will discover all JXTA resources that are on the local network or are known by the peer’s rendezvous peers. ...

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