Download The Peer Resolver Protocol

Department of Communications, Optics & Materials
Technical University of Denmark
JXTA protocols
Colin Chaballier
[email protected]
34352-Advanced Protocols
18/04/2006
JXTA
Peer-to-Peer Networking ?
a well-known subject (File Exchange, Instant Messaging ….)
Peer-to-peer networks are dedicated to their application
… a lack of inter-operability
… a lack of independence with platforms
- Transport Networks
- Operating System & programming language
A real need for an independent, adhoc, pervasive p2p network
>> JXTA !
JXTA
Agenda
1. Context & Overview
- What Jxta is
- Jxta’s philosophy
- An overlay network
2. Protocols
- Protocol stack overview
- Protocols description
- Peer Discovery Protocol
- Peer Resolver Protocol
- Rendez Vous Protocol
- Endpoint Routing Protocol
- Pipe Binding Protocol
- Peer Information Protocol
- Jxta 2 improvements
3. Discussion
- Jxta’s issues
- Implementations, applications and future
JXTA
1. Context & Overview
- What Jxta is
- JXTA’s philosophy
- An overlay network
2. Protocols
3. Discussion
What Jxta is
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A set of specifications by Sun Microsystems
Version 1 in June 2001
Version 2 in June 2003
Still improving …
Objective: to define protocols for generic peer-to-peer networking
Implementations proposed by Sun Microsystems on the Java platforms
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JXTA’s philosophy (1/2)
Jxta enables to build p2p applications on a common platform (JXTA)
with the following characteristics:
> scalability
> Robustness & fault-resistance
> Dynamic behavior & spontaneity
> self-organization
>> Creation of a new set of applications
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JXTA’s philosophy (2/2)
Organization of these applications:
> Services offered within peergroups
> Each peer is able to “provide” or “consume” a service
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An overlay network (1/2)
Illustration copied from the paper “Project JXTA: A Loosely-Consistent DHT Rendezvous Walker”,
B.Traversat and al., Sun Microsystems.
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An overlay network (2/2)
The basics elements of a JXTA network:
> Peer
The basic element, could be a PC, a cluster, a sensor …
> Peergroup
A group of peers with a common interest. Peers must be part of
the same peergroup to communicate.
> Service
Peers can proposes services within their peergroups.
> Endpoint
Abstraction of peers’ network interfaces. An endpoint can
matches with more than one peer (broadcast).
> Pipe
High level mean of transport between endpoints.
> Advertisement
Way to provide descriptions of every resources in the network.
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JXTA
1. Context & Overview
2. Protocols
- Protocol stack overview
- Protocols description
- Peer Discovery Protocol
- Peer Resolver Protocol
- Rendez Vous Protocol
- Endpoint Routing Protocol
- Pipe Binding Protocol
- Peer Information Protocol
- Jxta 2 enhancements
3. Discussion
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The Jxta protocol stack (1/2)
6 defined protocols for adhoc and p2p networking to :
• Route
• Discover
• Organize
• Monitor
• and communicate
… between peers
Without any assumptions on the underlying transport network
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The Jxta protocol stack (2/2)
1
2
5
6
3
4
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The Peer Discovery Protocol (1/2)
Description
Publish and discover ressources using advertisements
• Every network resources represented by an advertisement
(peer, peergroup, pipe, module …)
• A very simple and generic mechanism
• 2 messages types :
Discovery Query Message
lookup for a keyword for example
Discovery Response Message reply matching advertisements
• No guarantee of response to a query
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The Peer Discovery Protocol (2/2)
Messages
<?xml version=“1.0” encoding=“UTF-8”?>
<jxta:DiscoveryQuery>
<Type> . . . </Type>
The Discovery Query
Message structure :
<Threshold> . . . </Threshold>
<PeerAdv> . . .</PeerAdv>
<Attr> Name </Attr>
<Value> *sidus* </Value>
</jxta:DiscoveryQuery>
<jxta:DiscoveryResponse>
<Type> . . . </Type>
<Count> . . . </Count>
The Discovery Response
Message structure :
<PeerAdv> . . .</PeerAdv>
<Attr> Name. </Attr>
<Value> *sidus*</Value>
<Response Expiration= ‘’expiration time’’>
<!-- pipe adv., containing the string “sidus” in its name>
</Response>
</jxta:DiscoveryResponse>
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The Peer Discovery Protocol - Summary
• How to publish and discover network resources with advertisements
> Next step: Peer Resolver Protocol
1
2
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The Peer Resolver Protocol (1/2)
Description
• Spread generic queries to one or more peer inside a peergroup
• And matches responses to them
• 2 messages types :
Resolver Query Message
Resolver Response Message
• A unique ID for each query
• Best effort behaviour … any guarantee to get a response to a query
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The Peer Resolver Protocol (2/2)
Messages
<?xml version=“1.0” encoding=“UTF-8”?>
<jxta:ResolverQuery>
<Credential> . . . </ Credential>
<SrcPeerID> . . . </ SrcPeerID>
The Resolver Query
Message structure :
<HandlerName> . . .</HandlerName>
<QueryID> . . . </ QueryID >
<Query>
<!-- ex: Discovery Query Message -->
</Query>
</jxta:ResolverQuery>
<?xml version=“1.0” encoding=“UTF-8”?>
<jxta:ResolverResponse>
<Credential> . . . </ Credential>
The Resolver Response
Message structure :
<HandlerName> . . .</HandlerName>
<QueryID> . . . </ QueryID >
<Response>
<!-- ex: Discovery Response Message -->
</Response>
</jxta:ResolverResponse>
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The Peer Resolver Protocol - Summary
• How to send query-based messages through the network
> Next step: Rendez Vous Protocol
1
2
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The RendezVous Protocol (1/3)
Description
• Propagation of messages within a peergroup
• And control of propagation (TTL, loopback detection)
• Notion of rendezvous peers
Explicit connection between a simple peer and a rendezvous peer
• 3 types of messages :
LeaseRequest
LeaseGranted
LeaseCancelRequest
LeaseCancelled
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The RendezVous Protocol (2/3)
XML element
The rendezvous Propagate Message element:
<jxta:RendezVousPropagateMessage>
<MessageId> … </MessageId>
<DestSName> . . . </DestSName>
<DestSParam> . . . </DestSParam>
<TTL> … </TTL>
<Path> . . . </Path>
</jxta:RendezVousPropagateMessage>
MessageId : time in ms since propagation start
DestSName & DestSParam : name & parameters of the destination service
TTL : current TTL of the propagated message
Path: peer Ids of peer already visited
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The RendezVous Protocol (3/3)
Propagation Control
Loops:
With the path element, messages already processed on a peer are
discarded.
Expiration:
With the TTL element, messages are propagated until the TTL reach zero.
Duplication:
With the unique identifier, duplicated messages can be detected on peers.
> modification with version 2
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Partial summary: how to discover resources ?
Using the Peer Discovery Protocol, Peer Resolver Protocol, and Rendez Vous Protocol
1. Prepare the Discovery query
<jxta:ResolverResponse>
<jxta:ResolverQuery>
<jxta:DiscoveryResponse>
<jxta:DiscoveryQuery>
<Credential>
. . . </ Credential>
. . . </ Credential>
<Type>
<Type>. .. .. </Type>
.<Credential>
</Type>
2. Pack it with a Resolver Query
3. Send query
<HandlerName>
. .</HandlerName>
. . . </ SrcPeerID>
<Count>
. . . <SrcPeerID>
</Count>
<Threshold>
. . .. </Threshold>
<QueryID>
</ QueryID > . . .</HandlerName>
<PeerAdv>
....</PeerAdv>
<PeerAdv>..<HandlerName>
.. .</PeerAdv>
4. Propagate query with RVP
5. Peers look for the asked resource
6. Positive replies are sent back
7. Unpack the Resolver Response
8. Get Discovery Response
<Response>
<QueryID>
<Attr>
</Attr>
<Attr>Name.
Name
</Attr> . . . </ QueryID >
<!-- Discovery
Response Message -->
<Query>
<Value>
*sidus*</Value>
<Value>
*sidus*
</Value>
</Response>
<!-- Discovery
Query
Message -->
<Response
Expiration=
‘’expiration
time’’>
</jxta:DiscoveryQuery>
</jxta:ResolverResponse>
</Query>
<!-- pipe adv.,
containing the string “sidus” in its name>
</jxta:ResolverQuery>
</Response>
</jxta:DiscoveryResponse>
No
Peer 2
Yes
Peer 3
Peer 1
No
RendezVous Peer
No
Peer 4
Animation inspired from the book “JXTA” page 127, Brendon Wilson, New Riders Edition.
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> Next step: Endpoint Routing Protocol
1
2
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4
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The EndPoint Routing Protocol (1/4)
Description
Any assumption on the underlying transport network (even TCP/IP) …
… need to define a own routing protocol.
> A routing protocol
> A transport protocol
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The EndPoint Routing Protocol (2/4)
A Routing Protocol
• Route Query/Response Messages to find routes
• Best path decision: dependent of the application, not specified in JXTA.
• Allow NAT traversal (use of HTTP for transport)
<jxta:EndpointRouter>
The Route Query Message:
<Type> RouteQuery </Type>
<DestPeer> . . . </ DestPeer>
</jxta:EndpointRouter>
<jxta:EndpointRouter>
<Type> RouteResponse </Type>
<DestPeerIdTag> . . . </ DestPeerIdTag>
The Route Response Message:
<RoutingPeerIdTag> . . . </RoutingPeerIdTag>
<RoutingPeerAdvTag> . . . </RoutingPeerAdvTag>
<NbOfHops> … </NbOfHops>
<GatewayForward> @gw1 </GatewayForward>
<GatewayForward> @gw2 </GatewayForward>
…
</jxta:EndpointRouter>
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The EndPoint Routing Protocol (3/4)
A Transport Protocol
• Add routers path (as an XML element) to the sent message
The Endpoint Router Message element:
<jxta:JxtaEndpointRouter>
<jxta:Src> … </jxta:Src>
<jxta:Dest> … </jxta:Dest>
<jxta:Last> … </jxta:Last>
<jxta:NBOH>… </jxta:NBOH>
<jxta:GatewayForward> @gwForward1 </jxta:GatewayForward >
<jxta:GatewayForward> @gwForward2 </jxta:GatewayForward >
…
<jxta:GatewayReverse> @gwReverse1 </jxta:GatewayReverse >
<jxta:GatewayReverse> @gwReverse2 </jxta:GatewayReverse >
…
</jxta:EndpointRouter>
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The Endpoint Routing Protocol (4/4)
Message exchanges
No
Peer 2
Route Query Message
No
Route Response Message
Message to sent
Peer 3
+ Endpoint Router Message
Yes
Peer Router
Peer 1
Peer 4
private network
Peer Router
http transport
Within the same PeerGroup
Animation inspired from the book “JXTA” page 278, Brendon Wilson, New Riders Edition.
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The EndPoint Routing Protocol - Summary
• How to reach a peer in the network
> Next step: Pipe Binding Protocol
1
5
2
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4
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The Pipe Binding Protocol (1/2)
Description
• Used to bind network Endpoint and pipes input/output
• Pipes: abstraction to allow easy communication between endpoints
3 types of pipes: unicast, broadcast, and secure
Only mandatory support of unicast & asynchronous pipe type
Peer 2
broadcast pipe
Peer 1
Unicast pipe
Peer 3
Peer 4
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The Pipe Binding Protocol (2/2)
<jxta:PipeResolver>
• Pipe Binding Query:
<MsgType>Query</MsgType>
To discover listening peer
endpoints to a particular pipe
advertisement
<PipeId> … </PipeId>
<Type> … </Type>
<Cached> … </Cached>
<Peer> … </Peer>
</jxta:PipeResolver>
<jxta:PipeResolver>
• Pipe Binding Response:
Optional response to a Pipe
Binding Query
<MsgType>Answer</MsgType>
<PipeId> … </PipeId>
<Type> … </Type>
<Cached> … </Cached>
<Peer> … </Peer>
<Found> … </Found>
<PeerAdv> … </PeerAdv>
</jxta:PipeResolver>
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The Pipe Binding Protocol - Summary
• How to realize a high-level abstraction communication between endpoints
> Next step: Pipe Binding Protocol
1
5
2
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3
4
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The Peer Information Protocol
• A generic protocol to obtain peer status and monitoring information
> help load balancing in the network
• A simple Query/Answer mechanism
Peer Info Query and Peer Info Response Messages
• PeerInfoResponse Message fields:
•
•
•
•
•
•
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Peer uptime
Information timestamp
Response string (unspecified format)
Timestamp of last incoming and outgoing messages
Details on inbound and outbound traffic seen
Number of processed bytes
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Protocols description - Summary (1/2)
• How to Publish and discover network resources with advertisements
• How to send query-based messages through the network
• How to propagate messages within a peergroup
• How to reach a peer wherever in the network
• How to realize a high-level abstraction communication between endpoints
• How to monitor peers status
1
2
5
6
3
4
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Protocols description - Summary (2/2)
The “service” view
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Jxta 2 improvements
Version 1 since June 2001
Version 2 since February 2003 (now v2.3.5)
Improvement of overall performance and scalability with:
• New mechanisms for advertisement discovery (Rendezvous Super-peers)
• New mechanisms for NAT traversal (Relay Super-peers)
• Specification of a binary message format
•…
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Jxta 2 improvements
Advertisement discovery with Rendezvous Super-peers
• Loosely-consistent Distributed Hash Table
• Rendezvous Peer View
Illustration copied from the paper “Project JXTA 2.0 Super-Peer Virtual Network“,
B.Traversat and al., Sun Microsystems, 2003.
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JXTA
1. Context & Overview
2. Protocols
3. Discussion
- Jxta’s issues
- Implementations, applications and future
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Jxta’s issues
+ Abstraction: generic, multi-platform, multi-language …
+ Use of XML:
- easy understand & debug for developers
- flexibility
- No definition for services invocation
- Not optimized for application oriented: cost of the XML overhead
- Not optimized if usage of a reliable transport network (TCP/IP)
Trade-off: Performance vs. Flexibility
-> Not suitable for a short-term particular p2p application
-> But provide the flexibility for a long-term solution requiring scalability
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Implementations, applications and future
And now, what to do with JXTA protocols ?
1/ Developing a new application based on JXTA
> Choose an existing implementation of the JXTA specifications:
J2SE, J2ME, C, Perl, PocketPC … or do your proper implementation
> And fit the implementation to your application
Which components are useless ? What services to deploy ?
Topology of rendez-vous peers … etc.
2/ Contribute to the Project JXTA
> an open-source intiative still needing contributions …
3/ Or simply use a current application based on JXTA
• from the Jxta community: myJXTA, Gnougat, …
• more and more adopted by companies (Boeing, Verizon …)
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Summary
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• Specifications for a generic p2p network
 A global adhoc overlay network
 Peer group organization
 Any assumption on underlying transport network
 6 key protocols
 XML based
 Performance/flexibility trade-off
 Still in improvement - open source community
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References
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> Official web site for project JXTA: www.jxta.org
> Books:
• "JXTA in a nutshell", S. Oaks, B.Traversat and L.Gong, O'reilly.
• "JXTA", Brendon J. Wilson, New Riders Edition.
Freely available online at http://www.brendonwilson.com/projects/jxta-book/
> Articles and reports:
• "JXTA Technology Brings the Internet Back to Its Origin”.
Available at http://java.sun.com/developer/technicalArticles/JXTA/
• "Project JXTA Virtual Network",
B. Traversat et al., Sun Microsystems, 2002.
• "Project JXTA 2.0 Super-Peer Virtual Network",
B. Traversat et al., Sun Microsystems, 2003.
• "Project JXTA: A Loosely-Consistent DHT Rendezvous Walker ",
B. Traversat et al., Sun Microsystems.
• "The JXTA performance model and evaluation",
Emir Halepovic and Ralph Deters, Department of Computer Science, University
of Saskatchewan, Canada, published in the Elsevier database "Future
Generation Computer Systems", 2004.
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Thank you for your attention …
Questions ?
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