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A Hybrid Topology Architecture for P2P Systems. Ling Liu [email protected] Aameek Singh [email protected] College of Computing Georgia Institute of Technology. Road Ahead …. Introduction Structured and Unstructured Overlays Routing and Lookups, Anonymity, Data Placement

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A hybrid topology architecture for p2p systems l.jpg

A Hybrid Topology Architecture for P2P Systems

Ling Liu

[email protected]

Aameek Singh

[email protected]

College of Computing

Georgia Institute of Technology

ICCCN 2004

Road ahead l.jpg
Road Ahead …

  • Introduction

    • Structured and Unstructured Overlays

    • Routing and Lookups, Anonymity, Data Placement

  • Hybrid Topology Design

  • Performance Analysis

  • Conclusions and Future Work

  • Questions?

ICCCN 2004

Introduction l.jpg

  • Advent of Peer-to-Peer (P2P) Systems

    • [email protected] → Napster → Gnutella → Chord/Pastry

  • Overlay Networks

    • Data sharing

    • Data dissemination e.g. Application-level Multicast

    • Security

    • Voice over IP (VoIP)

  • Distinguishing Features

    • Overlay Topologies

    • Routing and Lookup

    • Level of Anonymity

ICCCN 2004

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Overlay Topologies

ICCCN 2004

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Our System

  • Decentralized Mutually Anonymous System

  • Maintains all “nice” DHT properties

    • Scalable & guaranteed lookup

  • Add-on unstructured topologies (Clouds)

    • Protect service requester and service provider

    • Use the underlying DHT routing in-between

  • To follow:

    • Identification of Topology Design Features

    • Design and Performance Analysis

ICCCN 2004

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What gives us anonymity?

  • Iterative Chord

    • Peers only give next-hop address

    • Querying peer revealed!

    • Also, Replying peer revealed to querying peer!

  • Recursive Chord

    • Follows Message Forwarding

    • Looks like Gnutella

    • Anonymous?


ICCCN 2004

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Clouds over DHT

DHT- Query Items mapped to Peers- Combine information from routing tables to identify the service provider

Our System- Query Items map to Clouds- Local Knowledge in clouds provides anonymity

ICCCN 2004

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  • Each cloud has a unique string name

  • Rendezvous Node

    • Entry Points

    • Node responsible for cloudname

    • There always exists one RN

      • Dynamics Handling

  • Issues

    • Reliability

    • Initial anonymity

ICCCN 2004

Routing l.jpg

  • Multi-phase mix

  • Gnutella like Routing in Clouds

    • Message Forwarding and Broadcasts

    • Provides Privacy

  • DHT routing between various clouds

    • For Guaranteed & Scalable Lookup

  • Appropriate linking of clouds to services

  • Limit size of clouds to prevent exponential costs

ICCCN 2004

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Mapping Services to Clouds

  • Semantic

    • Clouds where services offered are semantically linked

    • E.g. music sharing system – clouds containing files of one artist

  • Discovery of Service

    • Availability of a discovery of service mechanism

    • E.g. centralized directory

  • Dynamic

    • Infeasible to have a discovery mechanism

    • High performance applications with peers contributing resources

    • E.g. decentralized web crawling

ICCCN 2004

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R-Rings - Motivation

  • Membership based mapping?

  • Peers are too dynamic!

  • Mapping based on clouds?

  • Cloudname is static

ICCCN 2004

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  • Take a RN from each cloud and create new DHT ring

  • Always one representative per cloud at the same position

  • How to make its position static?

    • Each RN occupies position hquery(cloudname)

ICCCN 2004

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Routing Protocol

  • Three phases

    • Query forwarding in QueryCloud

    • Ring Phase: DHT lookup (Main/R-Ring)

    • Reply cloud broadcast

  • Crossover peers

    • Cross over from the first phase to the ring-phase

    • Should be unique

    • Equal distribution of load

  • Random walks

Querying Peer Anonymity

Scalable Routing

Replying Peer Anonymity

ICCCN 2004

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Routing Protocol

Query with TTL 4

Get First-Hop Address

DHT Phase (Query R-Ring)

Initiate Reply

Broadcast Query in ReplyCloud

ICCCN 2004

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Limiting Size of Clouds

  • Prevent exponential costs

  • System Parameters

    • R-diameter: Maximum distance from a RN (length dim)

    • Degree (m): Maximum number of neighbors (breadth)

  • Enforcing system parameters

    • In every ping cycle, peers exchange their distance vectors

    • Recursively evaluation of distance

    • Converges to the actual values

    • Temporary aberrations tolerated

ICCCN 2004

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  • Add-on unstructured topologies – Clouds

  • Map services to clouds

  • Routing

    • Random walk in query cloud

    • Crossover onto the ring

    • Broadcast in response cloud

  • Limit size of clouds

ICCCN 2004

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Performance: Scalability

- System is as scalable as popular DHT based systems in terms of both number of hops and aggregate messages transmitted - The messaging costs are higher because of broadcast in the response cloud

ICCCN 2004

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Effect of System Parameters



ICCCN 2004

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Security Analysis

  • Passive-logging Model

    • No online malicious behavior like protocol manipulation

    • Only offline sharing of logs

    • Goal: Identify origin/destination of messages

  • Prevention

    • Only one good edge required

  • Attack

    • Malicious Nodes need to surround the good node

  • Need more – the knowledge of it !

ICCCN 2004

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  • How to get the knowledge?

    • Saturate all m slots

    • Distance vectors information

    • Ping/Pong information

  • Best Attack Scenario

  • 1 bad node per good node

  • Requires extensive online manipulation – Not permissible

ICCCN 2004

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Cloud-creation Attack

  • Malicious nodes start a cloud and join en-masse

  • Effects vary with m

  • Greater m causes more compromises

  • Efficiency of attack decreases as more good nodes enter the cloud

    • Remember - 1 Good Edge

ICCCN 2004

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Block Attack

  • Malicious nodes join in groups, interspersing between good node arrivals

  • Find out intervals from historical analysis

  • Good nodes welcomed by one group of bad nodes and surrounded by another group

ICCCN 2004

Defenses l.jpg

  • Group strategy

    • Tough to achieve because bad nodes are indistinguishable

  • Get A Buddy Along

    • Join with a trusted friend and keep one edge with him/her

    • Trust

      • Only not to share logs

      • No privacy information revealed

  • Connect to RNs

  • Connect to peers from distinct domains only

ICCCN 2004

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  • Hybrid Topology – best from the unstructured & structured topologies

  • Scalable Routing, Mutual Anonymity, Guaranteed Lookups

  • Data Placement Benefits

  • Security Analysis – Anonymity compromising attacks

  • Securing the whole system – DHT vulnerabilities …

ICCCN 2004

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ICCCN 2004