A Survey on Layer-2 Scaling Solutions in Blockchain

PhD Qualifying Examination


Title: "A Survey on Layer-2 Scaling Solutions in Blockchain"

by

Mr. Zihuan XU


Abstract:

In recent years, blockchain technology has attracted much attention in both 
academics and industry due to its promising features in achieving immutable 
historical data and consensus among participants under a Byzantine failure 
environment. However, significant issues w.r.t. system throughput and 
scalability hinder the border adoption of blockchain-based decentralized 
applications. In particular, as an essential component of a blockchain system, 
the consensus mechanism enables participants to reach a consensus while also 
becoming the system bottleneck. Therefore, many efforts have been made to 
develop alternative consensus protocols or relieve the consensus bottleneck 
from other directions.

Recently, a new paradigm, namely layer-2 scaling, have made notable achievement 
in scaling blockchain systems such as Ethereum. Precisely, instead of directly 
resolving the system throughput and scalability issues on the layer-1 
blockchain, the idea of layer-2 scaling is to offload transaction processing to 
off-chain nodes, forming a layer-2 network of blockchain applications 
Meanwhile, the transaction processing results are finalized on-chain 
periodically.

This survey introduces five layer-2 scaling solutions, including channel, 
commit-chain, optimistic Rollup, zero-knowledge proof Rollup, and Validium. In 
the meantime, we categorize these five solutions into four types based on 
whether the data is available on-chain and how to prove the layer-2 transaction 
execution correctness. We discuss each solution in terms of four aspects: 
scalability, security, decentralization, and privacy. This survey provides a 
Systematization of Knowledge (SoK) of the layer-2 scaling solutions, highlights 
the performance of layer-2 solutions, and identifies their unsolved challenges, 
indicating promising avenues for future works.


Date:			Friday, 11 November 2022

Time:                  	4:00pm - 6:00pm

Venue:                  Room 5506
                         Lifts 25/26

Committee Members:	Prof. Lei Chen (Supervisor)
  			Prof. Bo Li (Chairperson)
 			Dr. Xiaojuan Ma
 			Dr. Yangqiu Song


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