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[Theory] P2P Network Topology and Content Routing

2019-03-21

## P2P Networks:

P2P Networks:

  • P2P networks overview
  • Centralized P2P networks
  • Purely decentralized networks
  • Hybrid P2P networks
  • Structured P2P networks

P2P Networks Overview

  • A logical overlay network built on top of the application layer
  • The overlay network consists of nodes/Peers/Nodes connected via P2P protocols to form the P2P network
  • Nodes: provide resources
  • Content routing: the function by which nodes locate resources — content routing / content search / routing queries
  • Content delivery ⚠️ (key point): fetching resources from multiple nodes in parallel
  • Other issues: firewall traversal (NAT)

Centralized Topology

  • Centralized P2P networks
  • The MP3-sharing software Napster

Advantages:

  • The biggest advantage is simple maintenance and efficient resource discovery.
  • Since resource discovery relies on a centralized directory system, the discovery algorithm is flexible and efficient, and complex queries are possible.

Disadvantages:

  • The biggest problem: like the traditional client/server structure, it is prone to a single point of failure
  • Problems such as “hot spot” access patterns and copyright disputes.

How it works:

  • A central index server stores the file index and location information for all files uploaded by users
  • Searches run on the server, which returns the users who hold the file
  • The requester connects directly to the file owner to transfer the file

Functions:

  • It was the first to separate file query from file transfer
  • It effectively saves central server bandwidth and reduces the system’s file transfer latency

Problems with the model:

  • If the central index server goes down, the entire network can collapse, so reliability and security are relatively low.
  • As the network grows, the cost of maintaining and updating the central index server rises sharply, making it expensive.
  • The central index server often triggers copyright disputes, and service providers can easily be held legally liable.

Applicability:

For small networks, the centralized topology has certain advantages in management and control; the model is not suitable for large-scale network applications.

Decentralized Unstructured Topology

  • Purely decentralized networks
  • The Gnutella network

Decentralized Structured Topology (also known as DHT networks)

  • Structured P2P networks

Partially Decentralized Topology

  • Hybrid P2P networks

References: