L
n. — network architecture; base-layer protocol
A Layer 1 (L1) network is the foundational base-layer blockchain protocol upon which all higher-order applications, scaling solutions, and secondary networks are built. L1 networks are responsible for the core functions of the blockchain: transaction settlement, consensus, data availability, and security. The L1 is the ultimate source of truth for the network's state. Prominent examples include Bitcoin, Ethereum, Solana, Avalanche, and Cardano. Each L1 makes distinct trade-offs across the blockchain trilemma — the competing demands of decentralization, security, and scalability.
TECHNICAL NOTE: L1 throughput is constrained by block size, block time, and consensus mechanism. Bitcoin processes approximately 7 transactions per second (TPS); Ethereum approximately 15–30 TPS on-chain. These limitations are the primary driver of Layer 2 scaling development. Modifications to L1 parameters require network-wide consensus and are typically implemented via hard or soft forks.
n. — scaling solution; off-chain computation
A Layer 2 (L2) is a secondary protocol or network built on top of a Layer 1 blockchain that processes transactions off the main chain while inheriting the security guarantees of the underlying L1 for final settlement. L2 solutions are designed to increase transaction throughput, reduce fees, and improve user experience without altering the base-layer protocol. The L2 periodically posts compressed transaction data or cryptographic proofs back to the L1, anchoring its state to the base chain's security. Major L2 categories include rollups (Optimistic and ZK), state channels, sidechains, and plasma chains.
TECHNICAL NOTE: The distinction between a true L2 and a sidechain is security inheritance: a genuine L2 derives its security from the L1 (users can exit to L1 without L2 operator cooperation), whereas a sidechain maintains its own independent validator set and security model. Ethereum's L2 ecosystem (Arbitrum, Optimism, Base, zkSync, Starknet) collectively processes multiples of Ethereum's own L1 throughput.
N
n. — network participant; distributed systems
In the context of blockchain networks, a node is any computing device that participates in the peer-to-peer network by maintaining a copy of the blockchain ledger, validating transactions and blocks, and relaying data to other network participants. Nodes are the fundamental units of a decentralized network's infrastructure; the aggregate of all nodes constitutes the network itself. Node types vary significantly in their resource requirements, responsibilities, and the degree to which they contribute to network security and decentralization.
INFRASTRUCTURE NOTE: The geographic and jurisdictional distribution of nodes is a key metric of network resilience. A network with nodes concentrated in a single country or cloud provider is vulnerable to regulatory shutdown or infrastructure failure. Bitcoin's publicly reachable node count is estimated at 15,000–20,000 globally; Ethereum's consensus-layer node count at approximately 6,000–10,000.
n. — network participant; consensus enforcement
A full node is a network participant that downloads, independently validates, and stores the complete history of a blockchain — every block and every transaction from the genesis block to the present. Full nodes enforce all consensus rules of the protocol without relying on any third party for validation. They are the backbone of a blockchain's decentralization and security: by independently verifying every transaction and block, full nodes ensure that no miner, validator, or other party can violate the protocol rules without detection and rejection by the network.
TECHNICAL NOTE: Running a Bitcoin full node requires approximately 600+ GB of storage (as of 2025) and grows continuously. Ethereum full nodes require 1–2 TB for execution-layer data. Full nodes do not necessarily participate in block production — they serve primarily as independent verifiers and data sources. All validators are full nodes, but not all full nodes are validators.
n. — lightweight client; simplified payment verification
A light node — also called a lightweight client or SPV (Simplified Payment Verification) client — is a blockchain participant that downloads only block headers rather than full block data, relying on the proof-of-work or proof-of-stake embedded in headers to verify the chain's validity. Light nodes do not independently validate all transactions; instead, they query full nodes for Merkle proofs to confirm that a given transaction is included in a block. Light nodes are designed for resource-constrained environments such as mobile wallets and embedded devices.
TECHNICAL NOTE: SPV was described in Section 8 of the Bitcoin whitepaper by Satoshi Nakamoto. The security trade-off is significant: light nodes trust that the longest chain is valid without verifying all transactions, making them susceptible to certain attacks (e.g., eclipse attacks, invalid block acceptance) that full nodes would reject. Light clients in Ethereum are being enhanced via the Ethereum Light Client Protocol and the Helios client.
n. — consensus participant; block producer
A validator node is a network participant in a Proof of Stake (PoS) or delegated consensus system that is responsible for proposing and attesting to new blocks, participating in the consensus process, and earning staking rewards in exchange for honest participation. Validators are required to lock up (stake) a specified amount of the network's native token as economic collateral — a deposit that can be partially or fully destroyed (slashed) if the validator acts dishonestly or fails to perform its duties. In Ethereum's PoS system, each validator requires a minimum stake of 32 ETH.
TECHNICAL NOTE: Ethereum's Beacon Chain launched in December 2020 with validator nodes forming the consensus layer. As of 2025, over 1 million validator instances are active on Ethereum. Validator duties include: block proposal (selected pseudo-randomly), attestation (voting on the canonical chain head), and sync committee participation. Slashing conditions include double voting (equivocation) and surround voting.
P
n. — network topology; distributed architecture
A peer-to-peer (P2P) network is a distributed computing architecture in which each participant (peer) communicates directly with other peers without routing through a central server or authority. In blockchain networks, the P2P layer is responsible for propagating transactions and blocks across the network, discovering new peers, and maintaining network connectivity. Each node maintains a list of known peers and relays data it receives to its connected neighbors, enabling information to propagate across the entire network without any single point of control or failure.
INFRASTRUCTURE NOTE: Bitcoin uses the Bitcoin P2P Protocol over TCP port 8333. Ethereum uses the devp2p protocol suite, including the RLPx transport protocol and the Ethereum Wire Protocol (ETH). P2P network topology directly affects transaction propagation latency, which in turn affects mining and validation strategy and the risk of network partitions. The gossip protocol is the primary mechanism for data propagation in most blockchain P2P networks.
n. — transaction queue; pending state; memory pool
The mempool (memory pool) is the holding area maintained by each full node where valid but unconfirmed transactions await inclusion in a block. When a user broadcasts a transaction to the network, it propagates via the P2P gossip protocol to nodes across the network, where it is validated against consensus rules and added to each node's local mempool. Miners and validators select transactions from the mempool — typically prioritizing those offering the highest fee per unit of block space — to include in the next block they produce.
TECHNICAL NOTE: Each node maintains its own independent mempool; there is no single global mempool. Mempools are bounded in size (Bitcoin's default is 300 MB); transactions that fail to be included within a timeout period (typically 14 days for Bitcoin) are evicted. During periods of high network congestion, mempools can contain hundreds of thousands of pending transactions, driving up fee markets. Mempool analysis is a key tool in blockchain forensics and MEV (Maximal Extractable Value) research.
B — C
n. — interoperability protocol; asset transfer mechanism
A cross-chain bridge is a protocol that enables the transfer of assets, data, or messages between two or more independent blockchain networks that do not natively share consensus or state. Bridges solve the fundamental interoperability problem of isolated blockchain ecosystems by creating a mechanism for representing assets from one chain on another. The most common bridge architecture involves locking assets on the source chain in a smart contract and minting a synthetic representation (wrapped token) on the destination chain, with the reverse process (burn-and-release) enabling redemption.
SECURITY NOTE: Cross-chain bridges represent one of the highest-risk attack surfaces in the blockchain ecosystem. The Ronin Bridge hack (March 2022, ~$625M), the Wormhole exploit (February 2022, ~$320M), and the Nomad Bridge attack (August 2022, ~$190M) collectively represent billions in losses. Bridge security depends on the trust model: trusted (custodial), trustless (on-chain verification), or hybrid. The Ronin Bridge was compromised via private key theft of validator nodes — a custodial trust model failure.
R
n. — Layer 2 scaling solution; off-chain execution
A rollup is a Layer 2 scaling solution that executes transactions off the main chain, batches them together, and posts compressed transaction data or cryptographic proofs to the Layer 1 for settlement and data availability. By moving computation off-chain while anchoring data and proofs on-chain, rollups can achieve transaction throughputs orders of magnitude higher than the base layer while inheriting its security. There are two primary rollup architectures: Optimistic Rollups (which assume transactions are valid and use fraud proofs to challenge invalid state transitions) and ZK-Rollups (which use zero-knowledge proofs to cryptographically verify the correctness of every batch).
TECHNICAL NOTE: Optimistic Rollups (Arbitrum, Optimism, Base) impose a withdrawal delay of typically 7 days to allow fraud proof challenges. ZK-Rollups (zkSync Era, Starknet, Polygon zkEVM) provide near-instant finality but require computationally intensive proof generation. EIP-4844 (Proto-Danksharding), activated on Ethereum in March 2024, introduced "blobs" — a new data availability mechanism that reduced rollup data posting costs by 10–100×.
S
n. — Layer 2 scaling; off-chain bilateral settlement
A state channel is a Layer 2 scaling mechanism that allows two or more parties to conduct an unlimited number of transactions off-chain by locking funds in a multi-signature smart contract on the base layer, exchanging signed state updates directly between participants, and settling the final state on-chain when the channel is closed. State channels are ideal for high-frequency, low-value interactions between known parties — such as micropayments or gaming moves — as they offer near-zero fees and near-instant finality for off-chain interactions. The Bitcoin Lightning Network is the most prominent implementation of payment channels, a subset of state channels.
TECHNICAL NOTE: State channels require both parties to be online to exchange state updates, and funds are locked for the channel's duration. Routing payments through a network of channels (as in Lightning) introduces additional complexity: liquidity management, routing fees, and the risk of channel force-closure. The Lightning Network held approximately 5,000 BTC in channel capacity as of early 2025. Ethereum's Raiden Network is the analogous implementation for ERC-20 tokens.
n. — horizontal scaling; database partitioning; L1 scaling
Sharding is a horizontal database partitioning technique adapted for blockchain networks to increase throughput at the base layer. In a sharded blockchain, the network is divided into multiple parallel sub-chains called shards, each processing a subset of the network's transactions and maintaining its own portion of the global state. Nodes are assigned to specific shards rather than processing all transactions, reducing the computational and storage burden on individual participants. Cross-shard communication — enabling transactions that span multiple shards — is the primary technical challenge of sharding implementations.
TECHNICAL NOTE: Ethereum's original roadmap included execution sharding (64 shards), but this was deprioritized in favor of a rollup-centric scaling strategy following the success of L2 solutions. The current Ethereum roadmap focuses on data sharding (Danksharding) — increasing data availability bandwidth for rollups rather than sharding execution. Near Protocol and Zilliqa are among the L1 networks that have implemented execution sharding in production.
A
n. — historical state storage; forensic infrastructure
An archive node is a full node that stores not only the complete blockchain history (all blocks and transactions) but also the complete historical state of the network at every block height — including all intermediate account balances, contract storage values, and state transitions that have since been pruned from standard full nodes. Archive nodes are essential for blockchain analytics, forensic investigation, and any application that requires querying historical on-chain state at arbitrary block heights. Standard full nodes prune historical state data to reduce storage requirements, retaining only the current state.
INFRASTRUCTURE NOTE: Ethereum archive nodes require approximately 12–20 TB of storage as of 2025 and continue to grow. Running a personal archive node is resource-intensive; most developers and analysts rely on commercial archive node providers (Alchemy, Infura, QuickNode, Ankr). Archive nodes are indispensable for blockchain forensics: reconstructing wallet balances at specific historical timestamps, tracing fund flows through smart contracts, and analyzing pre-exploit state are all archive-node-dependent operations.
n. — API endpoint; developer infrastructure; node interface
An RPC node is a blockchain node that exposes a Remote Procedure Call (RPC) interface — typically via HTTP or WebSocket — allowing external applications, wallets, and developers to query blockchain state and submit transactions without running their own node. RPC endpoints provide programmatic access to node functions: reading account balances, querying transaction history, calling smart contract functions, and broadcasting signed transactions. Ethereum's JSON-RPC API is the de facto standard interface, implemented by all major Ethereum clients (Geth, Nethermind, Besu, Erigon).
INFRASTRUCTURE NOTE: Centralized RPC providers (Infura, Alchemy, QuickNode) serve the vast majority of Web3 application traffic, creating a significant centralization risk. In November 2020, Infura experienced an outage that disrupted MetaMask and numerous DeFi applications globally — demonstrating the systemic risk of RPC provider concentration. Decentralized RPC networks (Pocket Network, Lava Network) aim to distribute this infrastructure layer. The eth_call, eth_getBalance, and eth_sendRawTransaction methods are among the most frequently used RPC endpoints.
{
"layer_0": {
"name": "Physical / P2P Network",
"protocols": ["TCP/IP", "devp2p", "libp2p"],
"function": "Peer discovery, data propagation"
},
"layer_1": {
"name": "Base Chain (Settlement Layer)",
"examples": ["Bitcoin", "Ethereum", "Solana"],
"tps_range": "7 – 65,000 TPS",
"node_types": ["Full", "Archive", "Validator", "Light", "RPC"]
},
"layer_2": {
"name": "Scaling / Execution Layer",
"types": {
"optimistic_rollup": "Fraud proofs · 7-day exit window",
"zk_rollup": "Validity proofs · instant finality",
"state_channel": "Off-chain bilateral · Lightning",
"plasma": "Child chains · mass exit risk"
},
"settlement": "Anchored to L1 via calldata / blobs (EIP-4844)"
},
"mem
