I'm just getting into JXTA for J2ME from a programming perspective and thought it was worth internalising and writing down the key JXTA concepts:
Peers - the networkable devices.
Virtual Networks - the network, which doesn't have to be "physical," that the peers form through JXTA. One important point about the virtual network is that peers are given logical addressed, not physical. addresses. I take this to mean that a peer can move from device to device. Through this, peers could something along the lines of the anthropomorphic idea of viruses and worms: a piece of software/application that moves from machine to machine.
Advertisements - XML descriptors of the peers and what services they provide. I assume that these "adverts," as one of the BBN people said, can also serve as generic envelopes for any type of meta-data. Every ad is assigned a lifetime, and there's some grounds keeping handling for dead ads.
Decentralized Resource Discovery - there are several types of peers (see below); those that help route traffic are called Rendezvous peers. These "RDV"'s facilitates looking up other peers; that is, they act as "ad servers," do caching, and even provide indexes. RDV's help keep track of "where" edge peers are, and what they provide. Even better, if the RDV doesn't know what you want, it helps you find other RDV's.
Ad Hoc Peer Groups - peers can be grouped together to create logical sets. Peer groups are used to established different policies (about routing, searching, access, etc.). If I recall and understood right, the policies are represented by ads.
Pipes - "very similar - in concept - to UNIX pipes." A JXTA pipe is just a generic conduit for peers to exchange data. If I understood right, a pipe will follow a peer through it's logical address. That is, if peer A is talking to a peer through a pipe, and peer A switches to a different machine, the pipe will follow the peer to it's new physical location.
Tyes of Peers:
Edge Peer - the classic client that produces and consumes data.
Relay Peer - virtual routers; "landmarks," that is, other peers use Relay Peers as known points in the network, e.g., "If you want to talk to me, talke to the landmark Relay Peer X."
Rendevous Peers - ad servers, caching, and indexing. This is different than Relay Peers in that actual network topology and information is stored in these peers...I think.
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You got it down ;-) I really like Your take on explaining logical
addresses, (that formulates something that would be possible with JXTA (in
theoretical)) ie. a peer moves from one device to another. altho that
explanation should come after the explanation that a peer can move from a
physical address to another without disruption of service, because of its
logical address (that is composed of a peerID in conjunction with a
pipeID). JXTA is IP agnostic and can therefore be seen to move in the
physical network while still being addressable in the virtual network.
