Computer Networking Lecture Notes

2014 November 17 • Peer-to-Peer Networks

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Outline

• Systems and applications.
• Peer-to-peer networking and architecture.
• Peer-to-peer routing.
• Data management.
• Load balancing and replication.
• Peer-to-Peer security.
• Trust and reputation.
• Peer-to-peer programming.

Peer-to-Peer Systems

• What are peer-to-peer networks?
• Networking and computing.
• Why bother? Benefits and applications.
• Challenges and design issues.
• Peer-to-peer vs grid computing.

Peer-to-Peer Architecture

• Taxonomy: where is control?
  • Also: how different are the parts?
• Central architecture.
  • Control is here; distinguishable parts.
• Decentralized architecture.
  • Control is everywhere, parts uniform.
• Hybrid architecture.
  • Managed dynamics.

Peer-to-Peer Routing

• Evaluation metrics: Efficiency, utility, coverage, scalability.
• Unstructured peer-to-peer network routing.
  • Routing with minimal knowledge.
• Structured peer-to-peer network routing.
  • Imposing structure to gain knowledge.
• Hybrid peer-to-peer network routing.
  • Structured systems in uncertain environments.

Systems and Applications

• What do peer-to-peer networks do?
• File sharing: Napster, Gnutella.
• Backup services: pStore, Pastiche.
• Data management: XML content routing.
• Peer-to-peer-based caching: Squirrel.
• Communication and collaboration: Jabber, Skype.
• Mobile applications.

Peer-to-peer vs Grid

• One point of view: there’s no difference.
• Data management vs manipulation.
  • Data management: databases, indexing.
  • Data manipulation: calculation, visualization.
• Peer-to-peer emphasizes data management.
• Grid emphasizes data manipulation.
• Both apply the same tools to different ends.

Data Management

• What peer-to-peer can do for data management.
  • What data management can do for peer-to-peer.
  • Improved navigation and query techniques.
• Data sharing: syntax vs semantics.
• Indexing.
• Information retrieval.
• Structured data management (databases).

Load Balancing and Replication

• Load balancing — uniform system use.
  • The system has no hot (over-used) or cold (under-used) spots.
  • A complex economic model.
• Replication — copying data.
  • A load balancing technique.
  • The central technique in reliability.

Load Balancing

• A resource management (allocation) problem.
  • Space, time, bandwidth, …
• Static or dynamic load balancing.
  • Usually not a choice, but a mixture.
• The three steps are measure, allocate, evaluation.
  • A cyclic sequence: evaluation → measurements.

Replication

• Copying resources for various objectives.
• Full or partial resource replication.
• Replication distribution based on measurements or pre-emptively.
  • And don’t forget undoing replication; caching.
• Changing replicas bring up consistency problems.
  • Immutable resources is a good dodge here.

Peer-to-Peer Security

• Directly attack peer-to-peer mechanics.
  • Stop or significantly impair network operation.
• Indirectly subvert peer-to-peer properties.
  • Attack content or indexing (rick-rolling).
  • Violate confidentiality or anonymity guarantees.
• Shades over into legal and political areas.

Peer-to-Peer Attacks

• Stop or significantly impair network operation.
  • Attacks to disable or hijack routing.
  • Storage and retrieval attacks.
  • Denial of service attacks.
• Recognizing and defending against attacks.

Peer-to-Peer Properties

• Indirectly subvert peer-to-peer properties.
• Data integrity and verification.
• Computational integrity: SETI@home.
• Free riding and fairness: bittorent.
• Privacy and anonymity: Freenet.
  • Overt and covert attacks.

Trust and Reputation

• Concepts.
• Trust models.
• Credential-based trust.
• Individual reputation and trust.
• Social relationships and trust.
• Trust management.

What is Trust?

• Trust defined psychologically, sociologically, statistically, …
• Trust in actions and recommendations.
• Measures of trust on various scales.
• Trust properties to work around or maintain.
  • Autonomy (context dependence).
  • Asymmetry
  • Quasi-transitivity
  • Multivalent

Trust Models

• A trust model realizes a particular trust strategy.
• A trust model can be based on reputation or credentials.
• Trust reputation is based on direct experience.
  • A trusts (doesn’t trust) B.
• Trust credentials is based on indirect reputation.
  • Vera “trusts” B; A “trusts” Vera.

Peer-to-Peer Programming

• How do you make a peer-to-peer network?
• Low-level peer-to-peer programming.
  • Assemble a network from first principles.
• High-level peer-to-peer programming.
  • Assemble a network from libraries or systems.
• Testing and deployment environments.
  • A tendency to combine testing and deployment.

Summary

• Peer-to-peer networks are distributed decentralized data managers.
• Distribution should bring advantages to reliability and performance.
• Usual networking issues and problems are amplified in peer-to-peer networks.
  • As well as other peer-to-peer specific issues and problems.
• Peer-to-peer networks are a protocol stack on top of the application layer.

References

• Introduction (Chapter 1) in Peer-to-Peer Computing by Quang Hieu Vu, Mihai Lupu, Beng Chin Ooi from Springer, 2010.
• Systems and Applications (Chapter 9), Ibid.

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This page last modified on 2014 November 17.