P2P - Peer-to-peer

3 minute read

Peer-to-Peer (P2P) Networking Peer-to-peer (P2P) networking is a decentralized network architecture where each participant (peer) can act as both a client and a server. Here are the key points:

Key Characteristics

Decentralization: There is no central server. Each peer is equally privileged and can initiate or complete any task.

Scalability: P2P networks can easily scale as more peers join the network.

Fault Tolerance: Since there is no single point of failure, the network is more resilient. If one peer fails, others can continue to operate.

How P2P Works

Discovery: Peers find each other through various methods, such as a central directory or using distributed hash tables (DHTs).

Handshake: Peers establish a connection by exchanging information about the protocols and data formats they support.

Data Exchange: Peers can directly share files or data with each other.

Protocols

BitTorrent: Used for efficient file sharing. Files are broken into small pieces, and peers download pieces from each other.

Gnutella: A decentralized file-sharing protocol where peers query each other to find files.

Kademlia (DHT): A protocol for storing and retrieving key-value pairs in a decentralized manner.

Bitcoin/Ethereum (Blockchain): Cryptocurrencies use P2P networks to maintain a distributed ledger of transactions.

Use Cases

File Sharing: Sharing large files (e.g., movies, software). Examples: BitTorrent.

Content Distribution: Distributing content efficiently by leveraging multiple peers. Examples: Some streaming services.

Cryptocurrencies: Bitcoin and Ethereum use P2P networks for secure and decentralized transaction processing.

VoIP: Voice and video calls over P2P networks. Examples: Skype.

Decentralized Applications (dApps): Applications that run on blockchain networks, providing greater security and resilience.

Imagine a 5 GB file to be distributed to 1K nodes. with 40Gbps (5GBps - GigaBytes per second) network (throughput for a good data center)

  • it will take a second to transfer the file from one one node to the other. Thus 1000 seconds for the transfer.

With peer-to-peer networks,

  • divide the 5GB files into a 1000 pieces of 1MB Each and let the peers transfer simultaneously

20K 100MB-1G blobs in under 30 sec

Tracker:

A tracker is a centralized server that acts as a directory for peers participating in a P2P network, typically associated with BitTorrent and similar file-sharing protocols.

Functionality:

  • Peer Registration: Peers connect to the tracker to register themselves and announce the files they have available for sharing.
  • Peer Discovery: Other peers looking for specific files query the tracker to get a list of peers currently sharing those files.
  • Coordination: The tracker helps coordinate connections between peers, facilitating the establishment of direct peer-to-peer connections for file sharing.

Trackers are centralized points of control in the network, meaning that their availability and performance can impact the overall usability of the P2P system.

Distributed Hash Table (DHT):

A DHT (Distributed Hash Table) is a decentralized method for storing and retrieving key-value pairs across a distributed network of nodes (peers).

Functionality:

  • Decentralization: Each peer in the network maintains a portion of the DHT, contributing to the storage and retrieval of data.
  • Key-Value Storage: Data (e.g., information about files, peer locations) is stored in the DHT using a distributed hash function, which determines where in the network each piece of data is stored.
  • Lookup: Peers can query the DHT to find the location of specific data ( e.g., which peers have a particular file).

DHTs are resilient to node failures and can scale effectively with the size of the network. They do not rely on a single point of failure or control.

BitTorrent also supports DHTs (using a protocol known as Mainline DHT) as an alternative to trackers for peer discovery and swarm management, enhancing robustness and decentralization.

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