The JXTA Protocols

1
The JXTA Protocols

• Di Valerio Carboni e Jonathan Sartori
• Corso di Sistemi Di Elaborazione a.a. 2003/2004
• Prof. G. Conte

2
What is JXTA ?
Di Valerio Carboni e Jonathan Sartori

• JXTA is a set of open, generalized peer-to-peer
  (P2P) protocols that allow any connected device
  on the network to communicate and collaborate as
  peers.
• The JXTA protocols are independent of any
  programming language,and multiple implementations
  (called bindings in Project JXTA) exist for
  different environments.
• Now we will focus on the Java implementation of
  JXTA

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A JXTA Overview
Di Valerio Carboni e Jonathan Sartori
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JXTA Protocols
Di Valerio Carboni e Jonathan Sartori

• Core Specification Protocols (lower level)
• Endpoint Routing Protocol (ERP)
• Peer Resolver Protocol (PRP)
• Standard Service Protocols (higher level)
• Peer Discovery Protocol (PDP)
• Peer Information Protocol (PIP)
• Pipe Binding Protocol (PBP)
• RendezVous Protocol (RVP)

• They allow to
• Discover resources through the whole JXTA
  network
• Get information about peers in the network
• Directly connect peers in order to exchange data

5
Peer Discovery Protocol (PDP)
Di Valerio Carboni e Jonathan Sartori

• The Peer Discovery Protocol (PDP) is a protocol
  designed to allow the discovery of advertisements
  published by peers within a peer group.
• Advertisements are used to describe and make
  available a wide variety of resources, including
  other peers, peer groups, pipes to exchange data,
  and ordinary content. All resources must have an
  advertisement associated with them.
• In the Java reference implementation, the
  DiscoveryService class allows peers associated
  with a particular group to publish and discover
  advertisements.
• The NetPeerGroup,the default group that all peers
  belong to, provides a discovery service to all
  peers without individual peers having to write
  their own service.

6
PDP Overview
Di Valerio Carboni e Jonathan Sartori
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PDP Java Bindings
Di Valerio Carboni e Jonathan Sartori
interface
implements
1

extends

• PDP also has a DiscoveryListener Interface, who
  calls the
• discoveryEvent method, called to handle an event
  from the Discovery Service.

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PDP principal methods
Di Valerio Carboni e Jonathan Sartori
From the DiscoveryServiceImpl class public
Enumeration   getLocalAdvertisements(String
attribute, String value) public int
getRemoteAdvertisements(String peerid,
String attribute,String value,                    
                    int threshold,
DiscoveryListener listener) public void
publish(Advertisement adv)    public void
publish(Advertisement adv,long tdv,
long tdvForOthers)   public void remotePublish(Ad
vertisement adv)

• Its an high-level protocol
• Its built on top of the Peer Resolver Protocol
  and Enpoint Routing Protocol
• May serve as a basis for more intelligent and
  high-level discovery services

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Peer Resolver Protocol (PRP)
Di Valerio Carboni e Jonathan Sartori

• Has the purpose of laying out a framework for
  generic query and response
• communication between peers
• Does not define any type of peer searching or
  discover service, but expects that
• such a service would be built using the framework
• Its a Core Specification Protocol (lower-level),
  so all the Standard Service
• Protocols are the beneficiaries of this service
• For example, the discovery service relies on the
  resolver service to handle the
• exchange of the query and response messages
  necessary for publishing and
• Discovery

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PRP Overview
Di Valerio Carboni e Jonathan Sartori
11
PRP Java Bindings
Di Valerio Carboni e Jonathan Sartori
The PRP has defined 3 interfaces

• The ResolverService does not process the queries,
  nor does it not compose reponses.
• Handling of queries, and composition of responses
  are left up to the registered handlers.
• Services that wish to handle queries, and
  generate reponses must implement QueryHandler

12
Endpoint Routing Protocol (ERP)
Di Valerio Carboni e Jonathan Sartori

• The Endpoint Routing Protocol (ERP) is a
  protocol designed to allow a peer to discover a
  possible route to send messages to another peer.
• A route is a sequence of hops (i.e. edge peers
  or rendez-vous).
• Why does JXTA need ERP?JXTA provides a dynamic
  network, where peers may enter or leave it
  spontaneously. So, peers need a routing mechanism
  that works even in situations in which the route
  between them is constantly changing.
• ERP is a core protocol, used by all others
  higher level. User can ignore how does it work,
  cause its functions are masked in a small set of
  methods.

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ERP Overview
Di Valerio Carboni e Jonathan Sartori
Peer 2
1. Peer 1 wants to send a message to Peer 4, but
is unable to connect to it directly. Peer 1 sends
a Route Query Message to its known simple peers
and rendezvous peers to try to determine a route
to Peer 4.
2. Rendezvous Peer 1, knowing a route to Peer 4,
sends a Route Response Message to Peer 1.
Peer 1
Rendezvous Peer 1
3. Peer 1 receives the Route Response Message and
adds an Endpoint Router Message to the message it
wants to send to Peer 4. It sends this message to
the first Endpoint Address provided in the
returned route information.
5. Peer 4 receives the Endpoint Router Message
and determines that it is the final destination
for the message. The original message is
extracted and sent to the appropriate service.
Peer 3
Peer 4
4. Peer 3 receives the Endpoint Router Message,
determines the next peer in the route (reading
the message header) and sends the message on to
the next Endpoint Address in the route.
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ERP Java Bindings
Di Valerio Carboni e Jonathan Sartori

extends

• ERP has a main class who provides all possible
  needed operations. This class
• uses many other subclasses to perform lower
  level operations.
• Under all, there is the transport layer (such as
  HTTP or TCP), which services
• are used by ERP to physically send messages from
  a peer to another.

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ERP principal methods
Di Valerio Carboni e Jonathan Sartori
public boolean  ping(EndpointAddress
addr) public Messenger  getMessenger(EndpointAddr
ess addr, Object hint) Users need only to know a
few methods, in fact all operations are
masked if (myEndpointService.ping(endpointAddress
)) Message message myEndpointService.newMessa
ge() message.setString("Message text", Hello
world!") EndpointMessenger messenger
myEndpointService.getMessenger(endpointAddress)
messenger.sendMessage(message)
When the getMessenger method is called,
EndpointRouter transparently determines route
information, either from cached information or
from sending Route Query Messages. Then the
method returns the appropriate messenger. The
implemented transport protocol used (such as
HTTP, TCP, etc.) provides the sendMessage method
who takes care about the physical transport.
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Rendez-Vous Protocol (RVP)
Di Valerio Carboni e Jonathan Sartori

• The Rendez-Vous Protocol (RVP) allows an edge
  peer to propagate messages across the JXTA
  network, beyond local subnetwork.
• RVP provides a virtual broadcast function
  independently of the underlying network
  capabilities.
• Before peers can use a rendezvous peer to
  propagate messages, they must connect to it and
  obtain a lease.
• RVP allows rendez-vous to choose their own
  policy about connection lease (implementing the
  RendezVousManager interface).
• RVP allows edge peers to customize their action
  when a connection is established or cut off
  (implementing RendezVousMonitor interface).

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RVP Overview
Di Valerio Carboni e Jonathan Sartori
2. Upon receiving the Lease Request Message, the
rendezvous peer decides whether to grant a
connection lease. If it does, it generates a
connection lease and sends a Lease Granted
Message to the requesting peer.
1. Peer 1 wants to use Rendezvous Peer 1 to
propagate a message within a peer group on its
behalf. It must first obtain a connection lease
with the rendezvous peer by sending a Lease
Request Message.
5. Peers receive the propagated message and route
the received message to the service specified by
the message's RendezVousPropagateMessage element.
7. Even peers not acting as rendezvous peers will
propagate messages. In this case, the propagation
will be limited to the local LAN segment.
4. When the rendezvous peer receives a message to
propagate, it checks that the source has already
been granted a lease. If it has, the rendezvous
peer propagates the message to each of the other
peers that currently hold a connection lease with
the rendezvous peer.
3. Peer 1 receives the Lease Granted Message. It
can now send messages to the rendezvous peer for
propagation to other peers.
6. A rendezvous peer might be a client of other
rendezvous peers. In this scenario, Rendezvous
Peer 1 is connected to Rendezvous Peer 2 and uses
Rendezvous Peer 2 to propagate the message to
peers that are also connected to Rendezvous Peer
2.
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RVP Java Bindings
Di Valerio Carboni e Jonathan Sartori
interface
implements

• Other interfaces net.jxta.rendezvous.RendezVous
  Monitor (implemented by the
• class net.jxta.impl.rendezvous.RdvMonitor, and
• net.jxta.rendezvous.RendezVousManager
  (implemented by the class
• net.jxta.impl.rendezvous.RdvManager)
• RVP has a RendezvousListener Interface too, who
  handles the events
• (such as connections, disconnections) fired by
  the RendezVous Service.

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RVP principal methods
Di Valerio Carboni e Jonathan Sartori
public void   connectToRendezVous(
PeerAdvertisement adv )public void
  disconnectFromRendezVous( PeerID peerID
) public void propagateToNeighbors(
Message msg, String serviceName, String
serviceParam, int TTL, String prunePeer ) public
void propagateInGroup( Message msg,
String serviceName, String serviceParam,
int TTL, String prunePeer ) public void
propagate( Message msg, String serviceName,
String serviceParam, int TTL ) public void
propagate( Enumeration destPeerIDs,
Message msg, String serviceName, String
serviceParam, int TTL ) public
boolean addPropagateListener(String
ServiceNameParams, EndpointListener
listener) public boolean removePropagateListener(S
tring name, EndpointListener listener)

• Latest version of RVP introduced the concept of
  Rendez-Vous Peer View (RPV).
• R.V. publish local advertisements on one (or
  more) R.V. peer, choosing them from their own
  Peer View, applying a hash function.
• R.V. who need an advertisement, use the same
  hash function on their RPV and obtains a R.V. If
  the RPV converges, the R.V. obtained will be the
  right one. Otherwise a Limited Range Walk will
  be performed.

20
Peer Information Protocol (PIP)
Di Valerio Carboni e Jonathan Sartori

• The Peer Information Protocol (PIP) is a
  protocol that allows a peer to monitor a remote
  peer and obtain information on its current
  status.
• Reasons for monitoring
• make services more efficients
• in commercial applications, determine the usage
  of a service and bill the service consumers for
  their use.
• Actually, the status informations provided are
  limited to the uptime of the peer and the amount
  of traffic processed in both incoming and
  outgoing directions.
• Peer Information Protocol is an optional JXTA
  protocol. This means that a target peer could not
  have implemented PIP service. In this case, all
  queries addressed to him would not have a
  response message.

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PIP Overview
Di Valerio Carboni e Jonathan Sartori
1. Peer 1 sends a Peer Info Query Message to a
specific peer, Simple Peer 2.
2. The Peer Info service on a simple peer
receiving the query searches and checks to see if
the querys targetPid matches the local peer ID.
If there is a match, the simple peer responds to
the source peer with a Peer Info Response
Message. Otherwise, the Peer Info service
propagate the query.
3. When the answer is notified, Peer 1 adds it to
his local cache.
22
PIP Java Bindings
Di Valerio Carboni e Jonathan Sartori
interface
implements
1

extends

• PIP has a PeerInfoListener Interface too, who
  allow the user to perform
• customized action each time a PeerInfoEvent is
  fired (by the PeerInfo Service)
• to signal a new query is incoming.

23
PIP principal methods
Di Valerio Carboni e Jonathan Sartori
public void   getRemotePeerInfo(ID peerID,
PeerInfoListener listener) public int
getRemotePeerInfo(ID peerID) public
PeerInfoResponseMessage getPeerInfoService()  pub
lic Enumeration getLocalPeerInfo(ID
peerID) public void flushAdverrtisement(ID
peerID) public void addPeerInfoListener(PeerInf
oListener listener) public boolean removePeerInfo
Listener(PeerInfoListener listener)

• Its the higher level and most work in progress
  protocol
• Its built on top of the PRP and RVP, which
  services are used to send messages
• PIPs functionality can be improved by the user
  (using the listener to handle request element in
  Query Messages)

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Pipe Binding Protocol (PBP)
Di Valerio Carboni e Jonathan Sartori

• It is based on assumption that a peer will
  create an input pipe and want to have remote
  peers connected to the pipe for information
  transfer
• The PBP defines a pipe, and specifies how the
  pipe can be used for communication between peers
  within a group.
• The pipe is an abstract communication channel
  built on an Internet transport protocol (such as
  HTTP or TCP/IP).
• It defines two ends of the pipe an input, or
  receiving, end and the output, or sending, end.
• It defines 3 type of pipe Unicast,
  UnicastSecure Propagate type

25
PBP Overview
Di Valerio Carboni e Jonathan Sartori
26
PBP Java Bindings
Di Valerio Carboni e Jonathan Sartori

• The PBP is an high-level protocol, built on top
  of the Endpoint Routing Protocol
• It implements interfaces from the Peer Resolver
  Protocol
• Its one of the most used protocols of the JXTA
  specification

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The future of JXTA
Di Valerio Carboni e Jonathan Sartori

• Implementation of new higher-level classes
• Substitution, correction and integration of old
  methods
• JXTA and Grid

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JXTA and Grid
Di Valerio Carboni e Jonathan Sartori
29
Example creation of an input pipe

• public class CreatePipe
• public static void main(String args)
•     try
•         PeerGroup netPG PeerGroupFactory.newNetP
  eerGroup()
•         catch (PeerGroupException e) /
  Unable to initialize the Peer Group /
•  
•     PipeService myPipeS netPG.getPipeService()
•     DiscoveryService myDiscoveryS
  netPG.getDiscoveryService()
•  
•     PipeAdvertisement pipeAdv (PipeAdvertisement)
  
•                                AdvertisementFactor
  y.newAdvertisement(PipeAdvertisement.getAdvertisem
  entType())
•     pipeAdv.setName("JXTAJWGProjectPropagatePipe
  ")
•     pipeAdv.setType(PipeService.PropagateType)
•     pipeAdv.setPipeID((ID) net.jxta.id.IDFactory.n
  ewPipeID(netPG.getPeerGroupID()))
•  
•     PipeMsgListener pipeListener new
  PipeMsgListener()
•         public void pipeMsgEvent(PipeMsgEvent e) 
  
•             try
•                 Message msg e.getMessage()

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Example search of an input pipe and connection
of an output pipe

• public class FindPipe
• public static void main (String args)    
• try
•         PeerGroup netPG PeerGroupFactory.newNetP
  eerGroup()
•         catch (PeerGroupException e) /
  Unable to initialize the Peer Group /
•  
•     PipeService myPipeS netPG.getPipeService()
•     DiscoveryService myDiscoveryS
  netPG.getDiscoveryService()
•  
•     DiscoveryListener myDiscoveryLis new
  DiscoveryListener
•         public void discoveryEvent(DiscoveryEvent
  e)
•             DiscoveryResponseMsg myMessage
  e.getResponse()
•             Enumeration enum myMessage.getRespon
  ses()
•             try
•                 PipeAdvertisement pipeAdv
  (PipeAdvertisement)enum.nextElement()
•                 OutputPipe myOutputPipe
  myPipeS.createOutputPipe(pipeAdv,0)
•                 catch(Exception ee)  /
  errore /
•  
•     myDiscoveryS.getRemoteAdvertisement(null,
  "Name", "JXTAJWGProjectPropagatePipe",1,
  myDiscoveryListener)