Peer-to-peer

Computers can work in teams.

In a team, every computer is a helper. One computer can ask for a file. Another computer can give that file.

This is different from a big boss computer. In a team, there is no boss. The computers share their own space. They share their power to think. This helps them work fast. It lets many people connect at once. It is a way for computers to be friends.

Computers can work together in a special way. This is called a peer-to-peer network. In this network, every computer is a peer.

A peer is a computer that acts as both a giver and a taker. One computer might ask for a file. Another computer then gives that file. This is different from a client-server model. In that model, one big boss computer provides everything to others.

There are two main ways these networks work. Some are called unstructured networks. In these, computers connect to each other in a random way. They are easy to build. They work well even if many computers join or leave at once. However, finding a rare file can be hard. You have to ask many peers to find it.

Other networks are called structured networks. These use a tool called a distributed hash table. This is a special way to organize data. It helps computers find even very rare files quickly.

Some networks are hybrids. They use a central server to help peers find each other. This can make searching much faster.

Computers can work together in many different ways. One way is called a peer-to-peer network, or P2P.

In this system, people share their own resources. These resources might be processing power, storage, or network capacity. Every participant acts as both a provider and a requester. This is very different from the client-server model. In that model, a central server provides everything to the clients.

In P2P, there is no single boss computer in charge. This makes the network more distributed across many different users.

There are two main ways these networks organize themselves. The first way is called an unstructured network. In these networks, peers connect to each other in a random way. They are easy to build and very strong. They work well even when many people join or leave.

However, finding a rare file can be a hard job. A peer must send a search query to many others. This creates a lot of extra traffic on the network. The second way is called a structured network. These use a tool called a distributed hash table, or DHT.

This helps peers find even very rare files quickly.

The idea of computers sharing has been around for a long time. The early Internet used a system called ARPANET. In ARPANET, every node could request and serve content. Later, a system called Usenet was made in 1979. It was a messaging system that used a decentralized model. In May 1999, Shawn Fanning introduced Napster. Napster was a music-sharing application. It helped make P2P networks famous to many people. It allowed users to form a virtual network without any central authority.

Different networks use different rules to find data. Unstructured networks like Gnutella or Kazaa use random connections. They are great for popular files that many people have. Structured networks like the Kad network use the DHT to assign files to specific peers. This is more efficient for searching. Some systems are hybrids. A hybrid model combines both ways of working. For example, Spotify used a hybrid model until 2014.

A central server might help peers find each other first. This makes the whole system perform much better.

Peer-to-peer technology is part of our everyday lives. You might use BitTorrent to share files over the Internet. You might even use Bluetooth or Miracast to show things on a screen.

These systems rely on the same P2P ideas. However, these networks also face some security challenges. Because every peer acts like a server, they can be targets for attacks. Some people might try to send false information to the network. This is called a routing attack. Even with these risks, P2P helps us connect and collaborate globally.

Peer-to-peer (P2P) computing is a distributed architecture for networking and computing.

In this system, participants share their own resources directly with others. These resources can include processing power, storage space, or network capacity. Every participant in a P2P network acts as both a resource provider and a resource requester. This is the opposite of the traditional client-server model. In a client-server model, central servers act as the providers while clients act as the requesters. P2P allows for a decentralized way to manage data and tasks across many different machines.

To understand how P2P works, we must look at the overlay network. P2P networks usually implement a virtual overlay network on top of the physical network topology.

While data travels over the underlying TCP/IP network, the peers communicate through logical links in the overlay. This makes the P2P system independent from the physical way the computers are connected. These overlays are used for indexing and peer discovery. This allows the network to organize itself without a central administrative authority.

There are two main types of P2P networks: unstructured and structured. Unstructured networks do not impose a specific design on the overlay network. Instead, nodes form connections to each other randomly.

These networks are easy to build and very robust. They handle "churn," which is when many peers join or leave the network frequently. However, searching in an unstructured network can be difficult. A peer must flood the network with search queries to find data. This creates high signaling traffic and uses a lot of CPU and memory. It also means finding rare data is unlikely.

Structured networks solve the search problem by using a specific topology. These networks often implement a distributed hash table (DHT).

A DHT uses consistent hashing to assign ownership of files to specific peers. This allows any node to find a resource efficiently by using key-value pairs.

Even if a file is extremely rare, the DHT helps locate it quickly. However, structured networks are less robust during high rates of churn. Maintaining the specific lists of neighbors required for routing can be difficult when nodes constantly change.

Some systems use a hybrid model to get the best of both worlds. A hybrid model combines P2P and client-server elements. For example, a central server might help peers find each other. This provides the centralized functionality needed for efficient searching. At the same time, it benefits from the decentralized power of many nodes. Spotify was an example of a hybrid model until 2014. These models often offer better performance than pure unstructured or structured networks.

The history of P2P goes back to the earliest days of networking. The first Request for Comments, RFC 1, mentioned principles that align with these ideas. The ARPANET was a successful precursor where every node could request and serve content. In 1979, Usenet was established as a decentralized messaging system. However, the concept became famous in May 1999 with Shawn Fanning's Napster.

Napster allowed users to form virtual networks independent of administrative authorities. This popularized the idea of users collaborating to create virtual supercomputers and filesystems.

P2P technology is used in many modern protocols and devices. BitTorrent is a well-known protocol used for file sharing over the Internet.

You might also use P2P in personal networks, such as Bluetooth radio or Miracast. These technologies allow devices to display and share data directly. Because every peer also acts as a server, these systems face unique security challenges. Malicious users can perform routing attacks, such as incorrect lookup routing. This happens when a node sends false results or incorrect routing updates to others.