1. Introduction
The Internet of Things (IoT) consists of lightweight, low-cost hardware devices designed to interact with physical and digital environments. Originally used in industrial automation during the 1990s, IoT devices now enable smart homes, autonomous vehicles, medical applications, and crypto wallets. However, securing the vast data generated by IoT devices remains a critical challenge. Traditional centralized solutions are being replaced by decentralized blockchain technology, which offers immutability, security, and low storage costs without relying on third-party trust.
Blockchain provides decentralization, security, and access control across sectors like banking, supply chain, NFTs, and decentralized finance (DeFi). Technically, blockchains are Byzantine fault-tolerant distributed ledgers (DLTs) that achieve state-machine replication via consensus protocols. While Bitcoin and Ethereum dominate the blockchain space, their block-based structures face scalability issues, high fees, and centralization risks due to mining.
Alternative DLTs like Directed Acyclic Graph (DAG)-based systems (e.g., IOTA) address these limitations by enabling feeless transactions and eliminating miners. IOTA’s Tangle ledger is particularly suited for IoT ecosystems due to its lightweight design and scalability. However, IoT devices increasingly operate in isolated networks, necessitating offline blockchain functionality—a key focus of this paper.
Key Contributions:
- Problem formulation: Hidden IoT devices and blockchain integration challenges.
- IOTA analysis: Existing offline Tangle provisions and limitations.
- Experimental validation: Code-level evaluation of IOTA’s offline capabilities.
2. Problem Statement
2.1 Hidden IoT Devices and Blockchain
IoT devices often lack timely hardware/software upgrades, exposing them to cyberattacks (e.g., Mirai botnet DDoS). To mitigate risks, organizations isolate IoT devices from public networks. However, this isolation complicates blockchain integration since transactions require periodic synchronization with public ledgers to achieve finality (irreversible state).
Challenges:
- Partial-synchrony: Isolated IoT devices lack continuous connectivity, hindering real-time blockchain updates.
- Offline finality: Transactions must be merged with public blockchains despite intermittent connectivity.
2.2 Offline Blockchain Scalability
Most scaling solutions (e.g., sidechains, Lightning Network) focus on block-based ledgers, which are ill-suited for IoT. DAG-based ledgers like IOTA offer potential for offline scaling, but mechanisms for merging offline transactions remain underdefined.
3. Related Work
| Blockchain | Type | Structure | Offline Support | Limitations |
|------------------|----------------|-----------------|-----------------|------------------------------|
| Bitcoin/Ethereum | Permissionless | Block-based | No | High fees, mining centralization |
| Byteball | Permissionless | DAG | No | Trusted witnesses required |
| JHdag | Permissionless | Block-DAG hybrid | No | Complex consensus rules |
| IOTA | Permissionless | DAG (Tangle) | Partial | Coordinator dependency |
Prior studies ([33]–[39]) assume IOTA supports offline transactions without empirical validation. Our work fills this gap by testing IOTA’s offline functionality under realistic conditions.
4. IOTA Background
4.1 Key Components
- Tangle: A DAG where each transaction validates previous ones, enabling parallel processing.
- Coordinator (COO): A central node that issues milestones for transaction finality.
- Milestones: Special transactions that confirm all referenced transactions, ensuring irreversibility.
4.2 Offline Tangle
Isolated nodes can process transactions offline, forming a sub-Tangle. These transactions remain unconfirmed until synchronized with the main Tangle via milestones.
Challenges:
- Tip selection: Offline transactions risk being classified as "lazy" and discarded if not merged promptly.
- Solidification delays: Nodes must validate historical transactions, slowing synchronization.
5. Offline Scaling Analysis
5.1 Time Bounds for Synchronization
Offline transactions must be broadcast within 180 seconds (15 milestones × 12-second intervals) to avoid rejection. Delays cause sub-Tangles to detach, wasting validation efforts.
Equation (1):
[ T_{\text{broadcast}} = T_{\text{solidification}} + \text{Network latency} ]
5.2 Experimental Results
- Tip Selection: Unconfirmed transactions were discarded after 80 seconds of isolation.
- Convergence: Only 60% of offline transactions achieved finality due to competition for milestone references.
6. Discussion
6.1 Feasibility of Offline IOTA
IOTA’s current design supports short-term offline operations (~3 minutes). Beyond this window, transactions risk being orphaned. Enhancements needed:
- Protocol-level trust mechanisms for offline sub-Tangles.
- Dynamic tip selection to prioritize offline transactions.
6.2 Cybersecurity Risks
Eclipsed nodes may face resource exhaustion from reattachment attempts. Future work should explore attack resilience.
7. Conclusion
IOTA’s Tangle offers partial offline functionality but requires protocol upgrades for robust IoT integration. Key findings:
- Time-bound synchronization is critical (≤180 seconds).
- Convergence rates drop significantly under prolonged isolation.
- Hybrid solutions (e.g., trust-based validation) could enhance offline scalability.
FAQ Section
Q1: Can IOTA support long-term offline transactions?
A: Currently, no. Transactions must sync within ~3 minutes to avoid rejection.
Q2: How does IOTA compare to Bitcoin for IoT?
A: IOTA’s feeless, DAG-based design is more suitable, but offline support remains limited.
Q3: What’s the biggest hurdle for offline IOTA adoption?
A: Coordinator dependency and tip selection algorithms hinder scalability.
👉 Explore more about blockchain scalability
👉 Learn how IOTA 2.0 aims to solve these challenges
This study bridges theory and practice, offering the first empirical validation of IOTA’s offline capabilities. Future blockchains must prioritize IoT-specific designs to enable seamless offline operations.
### SEO Keywords:
- **IoT blockchain integration**
- **IOTA Tangle offline scaling**
- **DAG-based distributed ledger**
- **Feeless transactions for IoT**
- **Byzantine fault tolerance**
### Formatting Notes:
- Headings (`##`, `###`) structure content hierarchically.
- Tables compare blockchain attributes concisely.
- **Bold** highlights key terms.