Bitcoin uses a P2P (peer-to-peer) network architecture based on the Internet, which means that every computer in the same network is peer-to-peer, and each node provides network services together without any "special" nodes. Each network node is connected to each other in a "flat" topology. There is no server, centralized service, or hierarchy in a P2P network: each node provides services to the outside world while using the services provided by other nodes in the network; P2P networks are therefore reliable, decentralized, and open. The early Internet is a typical use case of the P2P network architecture: the nodes in the IP network are completely equal. Today's Internet architecture has a hierarchical structure, but the IP protocol retains a flat topology. Outside of Bitcoin, the largest and most successful application of P2P technology is in the area of file sharing: Napster is a pioneer in this area, and BitTorrent is the latest evolution of its architecture.
The P2P network architecture used by Bitcoin is more than simply a choice of topology. Bitcoin was designed as a peer-to-peer digital cash system, and its network architecture is both a reflection of and a cornerstone of that core characteristic. Decentralized control is a core design principle, and it can only be achieved by maintaining a flat, decentralized P2P consensus network.
The "Bitcoin Network" is a collection of nodes that operate according to the Bitcoin P2P protocol. In addition to the Bitcoin P2P protocol, the Bitcoin network also contains other protocols. For example, the Stratum protocol is used for mining, and for lightweight or mobile bitcoin wallets. Gateway routing servers provide these protocols, use the Bitcoin P2P protocol to access the Bitcoin network, and expand the network to various nodes running other protocols. For example, the Stratum server connects all Stratum mining nodes to the main Bitcoin network via the Stratum protocol, and bridges the Stratum protocol to the Bitcoin P2P protocol. We use the term "extended bitcoin network" to refer to the overall network structure that contains the Bitcoin P2P protocol, the mining pool mining protocol, the Stratum protocol, and other protocols related to connecting Bitcoin system components.