Learning Objectives:
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Define Distributed Ledger Technology and its core principles
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Differentiate between blockchain and other DLT structures
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Understand the key properties of distributed ledgers
1.2.1: What is Distributed Ledger Technology (DLT)?
Definition:
Distributed Ledger Technology (DLT) is a digital system for recording transactions in which the transaction records and their chronological order are stored in multiple locations simultaneously, with no central data store or central authority.
Key Distinction:
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Distributed: Data is shared across multiple nodes
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Decentralized: No single point of control or failure
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Immutable: Once recorded, data cannot be altered
DLT vs. Traditional Database:
| Feature | Traditional Database | Distributed Ledger |
|---|---|---|
| Control | Central authority | Network consensus |
| Data Storage | Single location | Multiple copies |
| Data Modification | Can be altered | Immutable append-only |
| Trust Model | Trust in authority | Trust in mathematics |
| Single Point of Failure | Yes | No |
| Data Security | Permission-based | Cryptographic |
1.2.2: Types of DLT Architectures
1. Blockchain
A blockchain is a specific type of DLT where transactions are grouped into blocks, and each block is cryptographically linked to the previous block.
Blockchain Structure: ┌─────────────────────────────────────────────────────────────────────┐ │ Block N-1 Block N Block N+1 │ │ ┌─────────────┐ ┌─────────────┐ ┌─────────────┐ │ │ │ Block Hash │──────▶│ Block Hash │──────▶│ Block Hash │ │ │ │ Prev Hash │ │ Prev Hash │ │ Prev Hash │ │ │ │ Transactions│ │ Transactions│ │ Transactions│ │ │ │ Timestamp │ │ Timestamp │ │ Timestamp │ │ │ │ Merkle Root │ │ Merkle Root │ │ Merkle Root │ │ │ └─────────────┘ └─────────────┘ └─────────────┘ │ └─────────────────────────────────────────────────────────────────────┘ Properties: - Linear chain of blocks - Append-only structure - Immutable (once added, cannot be changed) - All nodes maintain full copy
2. Directed Acyclic Graph (DAG)
A DAG-based DLT allows multiple transactions to reference multiple previous transactions, creating a graph structure.
DAG Structure: ┌─────────────────────────────────────────────────────────────────────┐ │ │ │ ┌──────────┐ │ │ │ Tx 1 │ │ │ └────┬─────┘ │ │ │ │ │ ┌────▼─────┐ ┌──────────┐ │ │ │ Tx 2 │──│ Tx 3 │ │ │ └────┬─────┘ └────┬─────┘ │ │ │ │ │ │ ┌────▼─────┐ ┌────▼─────┐ ┌──────────┐ │ │ │ Tx 4 │──│ Tx 5 │──│ Tx 6 │ │ │ └──────────┘ └──────────┘ └──────────┘ │ │ │ │ Properties: │ │ - Multiple parents allowed │ │ - No blocks (transaction-level consensus) │ │ - High throughput │ │ - Asynchronous confirmation │ └─────────────────────────────────────────────────────────────────────┘
Examples of DAG-based DLTs:
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IOTA (Tangle)
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Nano (Block Lattice)
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Hedera Hashgraph (Hashgraph)
3. Hybrid DLT
Combines elements of blockchain and DAG.
Examples:
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DAG + Blockchain consensus
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Parent-child relationships with block finality
1.2.3: Properties of Distributed Ledgers
Core Properties:
| Property | Description | Importance |
|---|---|---|
| Immutability | Data cannot be altered after confirmation | Trust, auditability |
| Decentralization | No central point of control | Resilience, censorship resistance |
| Transparency | All transactions are visible | Trust, verification |
| Finality | Once confirmed, transaction is permanent | Settlement certainty |
| Availability | Data is always accessible | Resilience, uptime |
| Integrity | Data cannot be tampered with | Trust, security |
| Consistency | All nodes agree on the state | Consensus, reliability |
1.2.4: Consensus in Distributed Ledgers
Definition:
Consensus is the mechanism by which nodes in a distributed network agree on the state of the ledger.
Why Consensus is Needed:
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Nodes have different views (due to network latency)
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Some nodes may be faulty or malicious
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Need to prevent double-spending
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Need to order transactions
Types of Consensus Mechanisms:
| Mechanism | Description | Examples |
|---|---|---|
| PoW | Solve computational puzzles | Bitcoin, Ethereum (pre-Merge) |
| PoS | Stake tokens as collateral | Ethereum, Cardano |
| DPoS | Delegate voting power | EOS, Tron |
| PBFT | Practical Byzantine Fault Tolerance | Hyperledger Fabric |
| PoA | Authority nodes validate | POA Network |
| DAG | Transaction-level consensus | IOTA, Nano |
1. DLT vs Blockchain: Clarifying the Terminology
All blockchains are DLT, but NOT all DLTs are blockchains.
┌─────────────────────────────────────────────────────────────────────┐ │ │ │ Distributed Ledger Technology │ │ │ │ ┌─────────────────────────────────────────────────────────┐ │ │ │ │ │ │ │ Blockchain │ │ │ │ │ │ │ │ ┌──────────────────────────────────────────────────┐ │ │ │ │ │ Other DLTs │ │ │ │ │ │ (DAG, Hashgraph, etc.) │ │ │ │ │ └──────────────────────────────────────────────────┘ │ │ │ │ │ │ │ └─────────────────────────────────────────────────────────┘ │ │ │ │ Examples of DLTs that are NOT blockchains: │ │ • IOTA (Tangle - DAG) │ │ • Hedera Hashgraph (Hashgraph consensus) │ │ • Corda (Not all nodes store all data) │ │ │ └─────────────────────────────────────────────────────────────────────┘
2. Types of Nodes in a Distributed Ledger
| Node Type | Functions | Storage | Examples |
|---|---|---|---|
| Full Node | Validates all transactions, stores full blockchain | Full history | Bitcoin Core, Geth |
| Light Node | Verifies via Merkle proofs | Partial | Mobile wallets |
| Mining Node | Creates new blocks, validates transactions | Full history | Miners |
| Validator Node | Validates transactions, creates blocks in PoS | Full history | Validators |
| Archive Node | Stores full history, provides historical queries | Full + Archive | Block explorers |
3. CAP Theorem and DLT
CAP Theorem (Brewer’s Theorem):
A distributed system can only satisfy two of three properties:
| Property | Description | DLT Trade-off |
|---|---|---|
| Consistency | All nodes see same data | In PoW, finality takes time |
| Availability | System always responds | Decentralized networks are available |
| Partition Tolerance | System works despite network partitions | DLTs are partition tolerant |
DLT Trade-off:
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Most DLTs prioritize Partition Tolerance and Availability
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Consistency is eventual (not immediate)
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This is why Bitcoin takes ~1 hour for finality
4. Types of DLT Networks
Public (Permissionless) Networks:
| Feature | Description |
|---|---|
| Access | Anyone can join and participate |
| Read | Anyone can read transactions |
| Write | Anyone can write transactions |
| Consensus | Open to all participants |
| Examples | Bitcoin, Ethereum, Solana |
Private (Permissioned) Networks:
| Feature | Description |
|---|---|
| Access | Restricted to authorized participants |
| Read | Restricted to authorized participants |
| Write | Restricted to authorized participants |
| Consensus | Pre-selected validators |
| Examples | Hyperledger Fabric, Corda |
Consortium Networks:
| Feature | Description |
|---|---|
| Access | Controlled by a group of organizations |
| Read | Controlled by consortium rules |
| Write | Controlled by consortium rules |
| Consensus | Pre-selected by consortium members |
| Examples | R3 Corda, Energy Web Foundation |
5. DLT vs Blockchain: Technical Comparison
| Aspect | Blockchain | DLT (General) |
|---|---|---|
| Structure | Linear chain of blocks | Multiple structures |
| Consensus | Usually PoW or PoS | Various mechanisms |
| Data Model | Block-based | Transaction or record-based |
| Immutability | Strong | Strong |
| Scalability | Limited (PoW) | Various (some higher) |
| Energy Usage | High (PoW) | Varies |
| Use Cases | Cryptocurrencies, DeFi, NFTs | Supply chain, identity, IoT |