JXTA
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JXTA (Juxtapose) was an
open-source Open source is source code that is made freely available for possible modification and redistribution. Products include permission to use and view the source code, design documents, or content of the product. The open source model is a decentrali ...
peer-to-peer Peer-to-peer (P2P) computing or networking is a distributed application architecture that partitions tasks or workloads between peers. Peers are equally privileged, equipotent participants in the network, forming a peer-to-peer network of Node ...
protocol specification begun by
Sun Microsystems Sun Microsystems, Inc., often known as Sun for short, was an American technology company that existed from 1982 to 2010 which developed and sold computers, computer components, software, and information technology services. Sun contributed sig ...
in 2001. The JXTA
protocols Protocol may refer to: Sociology and politics * Protocol (politics), a formal agreement between nation states * Protocol (diplomacy), the etiquette of diplomacy and affairs of state * Etiquette, a code of personal behavior Science and technology ...
were defined as a set of
XML Extensible Markup Language (XML) is a markup language and file format for storing, transmitting, and reconstructing data. It defines a set of rules for encoding electronic document, documents in a format that is both human-readable and Machine-r ...
messages which allow any device connected to a network to exchange messages and collaborate independently of the underlying
network topology Network topology is the arrangement of the elements (Data link, links, Node (networking), nodes, etc.) of a communication network. Network topology can be used to define or describe the arrangement of various types of telecommunication networks, ...
. As JXTA was based upon a set of open XML protocols, it could be implemented in any modern computer language. Implementations were developed for Java SE, C/ C++, C# and
Java ME Java Platform, Micro Edition or Java ME is a computing platform for development and deployment of porting, portable code for embedded system, embedded and mobile devices (micro-controllers, sensors, gateways, mobile phones, personal digita ...
. The C# Version used the C++/ C native bindings and was not a complete re-implementation in its own right. JXTA peers create a virtual
overlay network An overlay network is a logical computer network that is protocol layering, layered on top of a physical network. The concept of overlay networking is distinct from the traditional model of OSI model, OSI layered networks, and almost always assum ...
which allows a peer to interact with other peers even when some of the peers and resources are behind
firewall Firewall may refer to: * Firewall (computing), a technological barrier designed to prevent unauthorized or unwanted communications between computer networks or hosts * Firewall (construction), a barrier inside a building, designed to limit the spre ...
s and NATs or use different network transports. In addition, each resource is identified by a unique ID, a 160 bit
SHA-1 In cryptography, SHA-1 (Secure Hash Algorithm 1) is a hash function which takes an input and produces a 160-bit (20-byte) hash value known as a message digest – typically rendered as 40 hexadecimal digits. It was designed by the United States ...
URN An urn is a vase, often with a cover, with a typically narrowed neck above a rounded body and a footed pedestal. Describing a vessel as an "urn", as opposed to a vase or other terms, generally reflects its use rather than any particular shape ...
in the Java binding, so that a peer can change its localization address while keeping a constant identification number.


Status

"In November 2010, Oracle officially announced its withdrawal from the JXTA projects". As of August 2011, the JXTA project has not yet been continued or otherwise announced to retain operations, neither a decision was made on the assembly of its Board nor an answer by Oracle regarding a pending request to move the source-code to Apache license version 2.


Protocols in JXTA

* Peer Resolver Protocol * Peer Information Protocol * Rendezvous Protocol * Peer Membership Protocol * Pipe Binding Protocol * Endpoint
Routing Routing is the process of selecting a path for traffic in a Network theory, network or between or across multiple networks. Broadly, routing is performed in many types of networks, including circuit-switched networks, such as the public switched ...
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 which have transient, low
bandwidth Bandwidth commonly refers to: * Bandwidth (signal processing) or ''analog bandwidth'', ''frequency bandwidth'', or ''radio bandwidth'', a measure of the width of a frequency range * Bandwidth (computing), the rate of data transfer, bit rate or thr ...
network connectivity. They usually reside on the border of the Internet, hidden behind corporate firewalls or accessing the network through non-dedicated connections. *A Rendezvous peer is a special purpose peer which is in charge of coordinating the peers in the JXTA network and provides 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 which are behind firewalls or NAT systems to take part in the JXTA network. This is performed by using a protocol which can traverse the firewall, like
HTTP HTTP (Hypertext Transfer Protocol) is an application layer protocol in the Internet protocol suite model for distributed, collaborative, hypermedia information systems. HTTP is the foundation of data communication for the World Wide Web, wher ...
, for example. 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.


Advertisements

An Advertisement is an XML document which describes any resource in a P2P network (peers, groups, pipes, services, etc.). The communication in JXTA can be thought as the exchange of one or more advertisements through the network.


Pipes

Pipes are a virtual
communication channel A communication channel refers either to a physical transmission medium such as a wire, or to a logical connection over a multiplexed medium such as a radio channel in telecommunications and computer networking. A channel is used for infor ...
used by JXTA to exchange messages and data. Pipes are asynchronous, unreliable, and unidirectional. There are basically three types of pipes: *
Unicast Unicast is data transmission from a single sender (red) to a single receiver (green). Other devices on the network (yellow) do not participate in the communication. In computer networking, unicast is a one-to-one transmission from one point in ...
* Uni-cast Secure * Propagate


Peer groups

A 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. A peer may play different roles in different groups; it may act as an edge peer in one group, but a rendezvous in another. 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 mechanism which 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 mechanism to enforce the consistency of all RPVs across the JXTA network, 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 Churn rate (also known as attrition rate, turnover, customer turnover, or customer defection) is a measure of the proportion of individuals or items moving out of a group over a specific period. It is one of two primary factors that determine the ...
, that is, a stable network where peers don't join or leave too frequently, the RPV list of each peer 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 publishes an Advertisement, the index of this advertisement is pushed to the rendezvous through a system called Shared Resource Distributed Index (SRDI). After that, the rendezvous applies a
Distributed Hash Table A distributed hash table (DHT) is a Distributed computing, distributed system that provides a lookup service similar to a hash table. Key–value pairs are stored in a DHT, and any participating node (networking), node can efficiently retrieve the ...
(DHT) function so that it can forward the index to another peer in the RPV list. For replication purposes, it will send this index to the neighbours of the chosen rendezvous peer in the RPV list. The lookup process requires the use of the same DHT function to discover the rendezvous peer which is in charge of storing that index. Once the rendezvous peer is reached it will forward the query to the edge peer which published the advertisement and this peer will get in touch with the peer which issues the query. If the DHT function cannot find a peer which is in charge of the advertisement then the query will be 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.


See also

*
Peer-to-peer Peer-to-peer (P2P) computing or networking is a distributed application architecture that partitions tasks or workloads between peers. Peers are equally privileged, equipotent participants in the network, forming a peer-to-peer network of Node ...
* Rendezvous protocol *
Chimera Chimera, Chimaera, or Chimaira (Greek for " she-goat") originally referred to: * Chimera (mythology), a fire-breathing monster of ancient Lycia said to combine parts from multiple animals * Mount Chimaera, a fire-spewing region of Lycia or Cilicia ...
.


References


External links


Official web site

Java implementation of JXTA

french site

Overview of JXTA


{{Authority control Distributed data storage Cross-platform free software Free network-related software Java platform Network protocols Sun Microsystems software