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JXTA (Juxtapose) is Open Source peer-to-peer platform created by Sun Microsystems in 2001. This platform is defined as a set of XML based protocols that allows any device connected to a network to exchange messages and collaborate in spite of the network topology. JXTA is the most mature p2p framework currently available and was design to allow a wide range of devices - PCs, mainframes, cell phones, PDAs - to communicate in a descentralized manner. Open source refers to projects that are open to the public and which draw on other projects that are freely available to the general public. ...
A peer-to-peer (or P2P) computer network is a network that relies on the computing power and bandwidth of the participants in the network rather than concentrating it in a relatively few servers. ...
Sun Microsystems, Inc. ...
The Extensible Markup Language (XML) is a W3C-recommended general-purpose markup language for creating special-purpose markup languages, capable of describing many different kinds of data. ...
As JXTA is based on a set of open protocols, it can be virtually ported to any modern computer language and these implementations are called (bindings). The Java programming language binding, JXTA2SE, is the most mature implementation, but there is a C programming language version, jxta-c, that is being actively developed as well. Java is an object-oriented programming language developed by James Gosling and colleagues at Sun Microsystems in the early 1990s. ...
The C Programming Language, Brian Kernighan and Dennis Ritchie, the original edition that served for many years as an informal specification of the language The C programming language is a standardized imperative computer programming language developed in the early 1970s by Dennis Ritchie for use on the Unix operating system. ...
JXTA peers create a virtual overlay network that allows a peer to interact with other peers directly even when some of the peers and resources are behind firewalls and NATs or use different network transports.
Protocols in JXTA
- Peer Resolver Protocol
- Peer Information Protocol
- Rendezvous Protocol
- Peer Membership Protocol
- Pipe Binding Protocol
- Endpoint Routing Protocol
Categories of Peers JXTA defines two main categories of peers: edge peers and super-peers. The super-peers can be further divided into rendezvous and relay peers. Each peer has a well defined role in the JXTA peer-to-peer model.
The edge peers are usually defined as peers that have transient, low bandwith network connectivity. They usually rely on the border of the Internet, hidden behind corporate firewalls or accessing the network through non dedicated connections.
A Rendezvous is a special purpose peer that is in charge of coordinating the peers in the JXTA network and provide the necessary scope to message propagation. If the peers are located in different subnets then the network should have at least one Rendezvous peer.
A Relay peer allows the peers that are behind firewalls or NAT systems to take part in the JXTA network. This is performed by using a protocol that can traverse the firewall as HTTP, for example. HTTP (for HyperText Transfer Protocol) is the primary method used to convey information on the World Wide Web. ...
It is worth noting that any peer in a JXTA network can be a rendezvous or relay as soon as they have the necessary credentials or network/storage/memory/CPU requirements.
Peer Groups The peer group provides a scope for message propagation and a logical clustering of peers. In JXTA, every peer is a member of a default group, NetPeerGroup, but a given peer can be member of many sub-groups at the same time.
Each group should have at least one rendezvous peer and it is not possible to send messages between two groups.
Rendezvous Network The Rendezvous peers have an optimized routing mecanism that allows an efficient propagation of messages pushed by edge peers connected to them. This is achieved through the use of a loosely consistent network.
Each Rendezvous peer maintains a Rendezvous Peer View (RPV), a list of known rendezvous peers ordered by the Peer ID. There is not any mecanism to enforce the correctness of the RPV, so a given RPV can have a temporary or permanent inconsistent view of the other rendezvous peers. As soon as there is a low churn rate, that is, a stable network where peers don't join or leave too frequently, then the RPV list of the various peers will converge as each rendezvous peer exchange a random subset of its RPV with other rendezvous peers from time to time.
When an edge peer publish an Advertisement, the index of this advertisement is pushed to the rendezvous through a mecanism called Shared Resource Distributed Index (SRDI). After that, the rendezvous applies a Distributed Hash Tables (DHT) function so that it can forward the index to another peer in the RPV list. As a caution, it will send this index to the neighbours of the chosen rendezvous peer in the RPV list.
The lookup process requires the same DHT function to discover the rendezvous peer that is in charge of that index. Once the rendezvous peer is reached it will forward the query to the edge peer that published the advertisement and this peer will get in touch with the peer that issue the query.
If the DHT function cannot find a peer that is in charge of the advertisement then the query will forwarded up and down the RPV list until a match is found, the query is aborted, or it reaches the limits of the RPV list. This process is called random walk.
Applications - MyJXTA - a general purpose p2p application that provides chat rooms, file exchanging, video and audio conferences.
See also A peer-to-peer (or P2P) computer network is a network that relies on the computing power and bandwidth of the participants in the network rather than concentrating it in a relatively few servers. ...
JINIâ„¢ (pronounced like genie, a pseudo-acronym: Jini Is Not Initials) is a network architecture for the construction of distributed systems where scale, rate of change and complexity of interactions within and between networks are extremely important and cannot be satisfactorily addressed by existing technologies. ...
JavaSpaces is a service specification. ...
External links - Official web site
- JXTA in a Nutshell
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