JXTA
Encyclopedia
JXTA is an open source
peer-to-peer
protocol specification begun by Sun Microsystems
in 2001. The JXTA protocols are defined as a set of XML
messages which allow any device connected to a network to exchange messages and collaborate independently of the underlying network topology
.
As JXTA is based upon a set of open XML protocols, it can be implemented in any modern computer language. Implementations are currently available for Java SE, C
/C++
, C# and Java ME. The C# Version uses the C++
/C
native bindings and is not a complete re-implementation in its own right.
JXTA peers create a virtual overlay network
which allows a peer to interact with other peers even when some of the peers and resources are behind firewall
s and NAT
s or use different network transports. In addition, each resource is identified by a unique ID, a 160 bit SHA-1 URN
in the Java binding, so that a peer can change its localization address while keeping a constant identification number.
JXTA strongly resembles Tapestry
.
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.
Each group should have at least one rendezvous peer and it is not possible to send messages between two groups.
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
, 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
(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.
Open source
The term open source describes practices in production and development that promote access to the end product's source materials. Some consider open source a philosophy, others consider it a pragmatic methodology...
peer-to-peer
Peer-to-peer
Peer-to-peer computing or networking is a distributed application architecture that partitions tasks or workloads among peers. Peers are equally privileged, equipotent participants in the application...
protocol specification begun by Sun Microsystems
Sun Microsystems
Sun Microsystems, Inc. was a company that sold :computers, computer components, :computer software, and :information technology services. Sun was founded on February 24, 1982...
in 2001. The JXTA protocols are defined as a set of XML
XML
Extensible Markup Language is a set of rules for encoding documents in machine-readable form. It is defined in the XML 1.0 Specification produced by the W3C, and several other related specifications, all gratis open standards....
messages which allow any device connected to a network to exchange messages and collaborate independently of the underlying network topology
Network topology
Network topology is the layout pattern of interconnections of the various elements of a computer or biological network....
.
As JXTA is based upon a set of open XML protocols, it can be implemented in any modern computer language. Implementations are currently available for Java SE, C
C (programming language)
C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....
/C++
C++
C++ is a statically typed, free-form, multi-paradigm, compiled, general-purpose programming language. It is regarded as an intermediate-level language, as it comprises a combination of both high-level and low-level language features. It was developed by Bjarne Stroustrup starting in 1979 at Bell...
, C# and Java ME. The C# Version uses the C++
C++
C++ is a statically typed, free-form, multi-paradigm, compiled, general-purpose programming language. It is regarded as an intermediate-level language, as it comprises a combination of both high-level and low-level language features. It was developed by Bjarne Stroustrup starting in 1979 at Bell...
/C
C (programming language)
C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....
native bindings and is not a complete re-implementation in its own right.
JXTA peers create a virtual overlay network
Overlay network
An overlay network is a computer network which is built on the top of another network. Nodes in the overlay can be thought of as being connected by virtual or logical links, each of which corresponds to a path, perhaps through many physical links, in the underlying network...
which allows a peer to interact with other peers even when some of the peers and resources are behind firewall
Firewall (computing)
A firewall is a device or set of devices designed to permit or deny network transmissions based upon a set of rules and is frequently used to protect networks from unauthorized access while permitting legitimate communications to pass....
s and NAT
Network address translation
In computer networking, network address translation is the process of modifying IP address information in IP packet headers while in transit across a traffic routing device....
s or use different network transports. In addition, each resource is identified by a unique ID, a 160 bit SHA-1 URN
Uniform Resource Name
A uniform resource name is a uniform resource identifier that uses the urn scheme and does not imply availability of the identified resource. Both URNs and URLs are URIs, and a particular URI may be a name and a locator at the same time.The functional requirements for uniform resource names are...
in the Java binding, so that a peer can change its localization address while keeping a constant identification number.
JXTA strongly resembles Tapestry
Tapestry (DHT)
Tapestry is a distributed hash table which provides a decentralized object location, routing, and multicasting infrastructure for distributed applications...
.
Protocols in JXTA
- Peer Resolver Protocol
- Peer Information Protocol
- Rendezvous Protocol
- Peer Membership Protocol
- Pipe Binding Protocol
- Endpoint RoutingRoutingRouting is the process of selecting paths in a network along which to send network traffic. Routing is performed for many kinds of networks, including the telephone network , electronic data networks , and transportation networks...
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 bandwidthBandwidth (computing)In computer networking and computer science, bandwidth, network bandwidth, data bandwidth, or digital bandwidth is a measure of available or consumed data communication resources expressed in bits/second or multiples of it .Note that in textbooks on wireless communications, modem data transmission,...
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, 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 used by JXTA to exchange messages and data. Pipes are asynchronous, unreliable, and unidirectional. There are basically three types of pipes:- UnicastUnicastright|200pxIn computer networking, unicast transmission is the sending of messages to a single network destination identified by a unique address.-Addressing methodologies:...
- Unicast 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
Churn rate , in its broadest sense, is a measure of the number of individuals or items moving into or out of a collective over a specific period of time...
, 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
Distributed hash table
A distributed hash table is a class of a decentralized distributed system that provides a lookup service similar to a hash table; pairs are stored in a DHT, and any participating node can efficiently retrieve the value associated with a given key...
(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.
Applications
- BoxCloud - a proprietary peer-to-peer Universal Content Sharing System
- OneDrum - a collaborative platform for MS Office
- b2een - a free peer-to-peer client used to exchange EDI messages by companies like Chevron, Areva or GE Oil&Gas
- Collanos WorkplaceCollanosCollanos Workplace is a proprietary teamwork software that ceased development in 2010.Installed on each team member’s computer, it builds a team environment and transparent knowledge store that allows to define and organize the content of project teams...
- a proprietary peer-to-peer team collaboration based on JXTA - Sixearch - a collaborative peer network application based on JXTA
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 .External links
- Official web site
- Java implementation of JXTA
- french site
- Italian JXTA Developer Community
- freenode:jxta JXTA Developer IRC Channel
- Overview of JXTA