IOTA-based Directed Acyclic Graphs without Orphans

TL;DR

This paper proposes a modification to the IOTA DAG architecture that guarantees all transactions are validated in finite time, addressing the orphaning problem and maintaining scalability and speed advantages.

Contribution

A simple modification to the Tangle's attachment mechanism is introduced, ensuring eventual validation of all transactions in DAG-based DLT systems.

Findings

Modified attachment mechanism prevents orphaned transactions.

Fluid model analysis confirms finite-time validation.

Simulations validate theoretical results for finite rates.

Abstract

Directed Acylic Graphs (DAGs) are emerging as an attractive alternative to traditional blockchain architectures for distributed ledger technology (DLT). In particular DAG ledgers with stochastic attachment mechanisms potentially offer many advantages over blockchain, including scalability and faster transaction speeds. However, the random nature of the attachment mechanism coupled with the requirement of protection against double-spend transactions leaves open the possibility that not all transactions will be eventually validated. Such transactions are said to be orphaned, and will never be validated. Our principal contribution is to propose a simple modification to the attachment mechanism for the Tangle (the IOTA DAG architecture). This modification ensures that all transactions are validated in finite time, and preserves essential features of the popular Monte-Carlo selection algorithm. In order to demonstrate these results we derive a fluid approximation for the Tangle (in the limit of infinite arrival rate) and prove that this fluid model exhibits the desired behavior. We also present simulations which validate the results for finite arrival rates.