Jxta Tutorial Part1a

8/3/2019 Jxta Tutorial Part1a

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Project JXTA Guide to a peer-to-peer

frameworkEkaterina ChtcherbinaSiemens AG, Corporate TechnologyMunich

Thomas WielandSiemens AG, MunichUniversity of Applied Sciences, Coburg


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2 Siemens CT, Chtcherbina/Wieland, 2002

High-level agenda

!

Introduction! Peer-to-Peer Computing

!

The Project JXTA! JXTA Concepts

! JXTA Protocols

! "Hello JXTA-World"


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Introduction: Benefits of

Peer-to-Peer Computing


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5 Myths about P2P

!

It is always fully decentralized! P2P is about People-to-People

communication

! It is only about file sharing

! P2P is not secure

! P2P is not scalable



Distributed Search



Multi-user applications and

games


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Auctions


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Collaboration


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Resource sharing


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Distributed storage and file

sharing


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Blackboards


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Examples of P2P

Applications! Building facilities (sensor equipment)

! Collaboration work support (developmenttools, data sharing)

!

Medicine (effective collaboration, filesharing, distributed data processing)

! Building site automatization

! Business & entertainment communicationsupport

! Cars (driver support, location based

services, car tracking)


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Peer-to-Peer Computing


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What is Peer-to-Peer

Networking?! Traditional P2P network definition (comp. sc.

encyclopedia):A type of network in which each workstation hasequivalent capabilities and responsibilities. This differsfrom client/server architectures, in which some computersare dedicated to serving others.

! Our P2P network definition:An adaptive, self-configuringnetwork which does not rely oncentral servers. The peers in aP2P network are devices that canact as both servers and clients(servents).


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Disadvantages of

Client/Server Systems! Central servers (or server clusters)

are potential bottlenecks and singlepoints of failure of distributed

systems" P2P allows for efficient use of

resources and robustness


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Peer-to-peer and Ad Hoc

Networks! Ad hoc networks require self-

configuration! Dynamic environment, unstable connectivity,

infrastructureless

! Issues: addressing, service discovery &advertisement, dynamic service composition,connection mgt., routing

" P2P enables self-configuration ofdynamic distributed systems


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Messages in C/S and P2P

Server

ServerCache

Traditional trafficcongestion zone

Client

Client

Client

Client

Client

ClientClient

Client

Peer

Peer

Peer

Peer

Peer

Peer Peer

Peer


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Centralized Distributed

Computing! Distributed networking technologies

such as DCOM, CORBA and WebServices currently rely on a priori

known directory servers (registry,naming server, UDDI, etc.)

DatabaseServer

ServiceClient

1.

3.

2.


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Centralized Distributed

Computing (2)! Distributed auto-configuration

technologies such as Jini also rely ondirectory servers

" P2P plug and play technologiessuch as UPnP are more suitable forinfrastructureless environments

Peer

Peer

Peer

Peer

Peer


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Special Features! Decentralized

! Scalability/Redundancy/Fault tolerance

! P2P networks scale well with increasing

numbers of users! Multiple distributed copies of of frequently

accessed resources

! Nondeterministic! Peers can appear and vanish spontaneously

! Behaviour is less predictable


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Requirements for P2P

Systems! Metadata/Interoperability

! When are they essentially independent ?

! Encapsulation? Privacy? Trust?

! Discovery! Who is out there ?

! How do I reach them ?

!

Messaging! QoS Security Trust/Reputation

! Peer-to-peer interaction issues


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Security in P2P Networks


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Security Issues! Authentication

! The process of determining whether or notsome entity is in fact who that entity declaresitself to be.

! Authorization! Process of giving an authenticated entity

permissions to do some action or access some

resource! Encryption and confidentiality

! Integrity


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Challenges in P2P Systems! Memberships and groups are dynamic

! People do not trust each other! Each peer is untrusted! Peers don't have trust relationships

! Unpredictable network latencies! Firewalls and other barriers! No central services (especially no directory)! Individuals can cause local damage that spreads

! Every peer may run run different software! Code may be mobile! Complex systems: hard to understand


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Solutions! Mostly based on "web of trust"

! A trusts B, B trusts C, so A can also trust C! Users exchange their public keys and encrypt messages

with their private keys! Enrich by reputations

Assign reputations to entities Allow others to retrieve reputations Use reputation to build trust relationships Example: eBay

!

Alternative: centrally issued group membershipcertificates (PKI)! Introduces dependencies from a server-like

infrastructure component

F th P ibl S it


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Further Possible Security

Tools! Encryption

! Authentication

! Firewalls

! May be installed on each peer! Drawbacks: Block all traffic on port, not

application; generally static rulesets

! Sandboxes! Essential for mobile code systems!

! E.g. in Java/JVM, .NET/CLR


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Search in P2P Networks

Di t ib t d S h


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Distributed Search:

Network Topology Based

Centralized(e.g. Napster)

Decentralized(e.g. Gnutella)

!Relies on the organization of the peers within thenetwork to route requests

!Optimization focuses on the reduction of the

diameter (no. of hops, round trip time) of thegraph representing the distributed network

Di t ib ted Se h Content


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Distributed Search: Content

Mapping Based! Content addressable networks:

distributed hash table. Content (orpointer to content) is stored in assignedpeers

" not a practical approach for contentdescribed by multiple attributes

! Publish/subscribe networks: peers agreeon a certain query and advertisementtemplate. Content based routing.


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Hybrid approach:

locally centralized +globally decentralized +publish/subscribe

(e.g. JXTA Search)

Hybrid Search

$ No perfect solution, choice

depends on the application

SuperPeer

Support for Message


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Support for Message

Exchange! Routing in multi-hop ad hoc networks

! Caching mechanism (relaying) for overcoming! Disruptive connectivity

! Firewalls

RelayPeer

MobilePeer

PeerA

PeerB

Firewall

Peer

C

RelayPeer

Polling


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Peer-to-Peer Systems! P2P platforms

! Sun Microsystems:JXTA

! Distributed computing

! SETI@home! Entropia

! File sharing

! Freenet! Gnutella

! KaZaA

! Messaging

frameworks! Open Source: Jabber

! Collaboration

! Engenia Software, Inc

! Others

! Magi: Endevors


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Project JXTA


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What is JXTA?conceptual framework for Peer-to-Peer applications

! serves as a specification, an effort to create acommon platform for building distributed servicesand applications

! neither a standalone Peer-to-Peer application nora concrete framework implementation!

! But: Sun has provided a reference implementation(in Java) which incorporates the specifiedcomponents

! Napster, Gnutella, Freenet & Co. provide userswith limited ability to share resources and are

unable to share data with other, similarapplications


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The Project JXTA! Started as a research project at Sun

Microsystems by Chief Scientist Bill Joy! First official release of a Java reference

implementation in April 2001

! Since then put under an open-source license

The name JXTA is derived from the wordjuxtapose,meaning to place two entities side-by-side or in close

proximity. By choosing this name, the developmentteam at Sun recognized that P2P solutions wouldalways exist alongside the current client/serversolutions, rather than replacing them completely.

Brendon Wilson


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Key Assumptions! Platform Independence (any language, any OS, any

hardware)! But: JXTA dependence! Allow for absolute heterogeneity of peers! Highly unreliable & changing network

environment! Asynchronous,Unreliable,Uni-directional

transport! Idempotent protocol exchanges No protocol

state! Applications to build their own security &

encryption models


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Technology! JXTA technology is based on XML, Java

technology, and key concepts of UNIXoperating system! Transmitted information is packaged as

messages! Messages define an XML envelop to transferany kind of data

! The use of Java language is not required! JXTA protocols can be implemented in C,

C++, Perl, or any other programminglanguage


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JXTA Concepts


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JXTA ArchitectureApplication Level

JXTA Services

JXTA Platform

pipes peers peer groups

Components

resolver pipe discovery membership

peer groups

Core Services

propagation service

router and relay services

transports


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Key Aspects! XML documents (advertisements)

used to describe network resources

! Abstraction of pipes to peers, and

peers to endpoints! without reliance upon a central

naming/addressing authority! A uniform peer addressing scheme

(peer IDs)


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Peers and Peer Groups

Peer

Peer Group

Net Peer Group


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Pipes

Peer A

Peer B

Point-to-point pipe

Peer A

Peer B

Peer C

Peer D

Peer E

Propagate pipe


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Advertisements! Representation of JXTA resources

! Like peers, peer groups, pipes etc.

! Metadata structures

! Used to decribe and publish peerresources, e.g.! Peer advertisement: Comprises name, ID,

endpoints, etc.

! Peer group advertisement: name, ID,decription, specification

! Pipe advertisement: ID, pipe type


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Kinds of peers! Minimal peer

! Simple peer

! Rendevour peer

! Relay peer


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Security in JXTA! Usual issues

! Confidentiality, integrity, availability - authentication, accesscontrol, encryption, secure communication, etc.

! Developing more concrete and precise securityarchitecture is an ongoing project

! JXTA does not mandate certain security polices, encryptionalgorithms or particular implementations!

! JXTA 1.0 provides Security Primitives:

! crypto library (MD5, RC4, RSA, etc.)

! Pluggable Authentication Module (PAM)

! password-based login

! transport security mechanism modeled after SSL/TLS


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Security Model! Role based trust model with four basic requirements

! Confidentiality! Authorization! Data Integrity! Refutability

! XML messages allow meta data such as credentials,

digests,certificates! Credential a token when presented in a message

uniquely identifies the sender, helps verify the sendersright to send a message to the endpoint

!

Credential default mechanism, Applications to implementmechanisms for better security! Need to establish trust among peers


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Summary


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Lessons from P2P! P2P is not a new concept, but it offers new possibilities

!

P2P applications! Sharing of files and other resources

! Distributed computation

! Instant messaging

! Self-configuring compound services! P2P applications need a standard open platform

! P2P networking does not suit to all application scenarios

! No QoS guarantee (variable connectivity)

! Hybrid solutions

JXTA summary (for the


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y (

moment ...)! JXTA An open-source framework and launching pad for

p2p systems! Aims to be Interoperable, platform independent and

ubiquitous! Peers are required to implement a low over-head stack of

six JXTA protocols that standardize

! Peer discovery! Self organization into peer groups! Peer-to-peer Communication! Peer monitoring

!

Challenges! Naming & Binding services! Security & Trust models! Solutions to overcome limitations on NAT gateways &

firewalls


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Thanks! Stay tuned for more details to come

! Any Questions?

Documents

Jxta Tutorial Part1a