# When Internet of Things Meets Blockchain: Challenges in Distributed Consensus

## TL;DR

This paper reviews blockchain consensus mechanisms, highlighting their importance in IoT, compares PoW, PoS, Tangle, and Hashgraph, and discusses future challenges for DAG-based consensus in IoT systems.

## Contribution

It provides a comprehensive comparison of traditional and DAG-based consensus mechanisms for IoT, emphasizing their suitability and challenges.

## Key findings

- DAG-based consensus mechanisms like Tangle and Hashgraph are more suitable for IoT than PoW and PoS.
- PoW and PoS have limitations in IoT environments such as high energy consumption and scalability issues.
- Future challenges include addressing security, scalability, and efficiency of DAG-based consensus mechanisms.

## Abstract

Blockchain has been regarded as a promising technology for Internet of Things (IoT), since it provides significant solutions for decentralized network which can address trust and security concerns, high maintenance cost problem, etc. The decentralization provided by blockchain can be largely attributed to the use of consensus mechanism, which enables peer-to-peer trading in a distributed manner without the involvement of any third party. This article starts from introducing the basic concept of blockchain and illustrating why consensus mechanism plays an indispensable role in a blockchain enabled IoT system. Then, we discuss the main ideas of two famous consensus mechanisms including Proof of Work (PoW) and Proof of Stake (PoS), and list their limitations in IoT. Next, two mainstream Direct Acyclic Graph (DAG) based consensus mechanisms, i.e., the Tangle and Hashgraph, are reviewed to show why DAG consensus is more suitable for IoT system than PoW and PoS. Potential issues and challenges of DAG based consensus mechanism to be addressed in the future are discussed in the last.