Overview of Qitmeer BlockDAG Technology
Bitcoin is based on the emergence of e-cash payment tools. What it wants to build is a truly decentralized payment network and ensure fairness by voting of computing power. After 10 years of testing, it has been a classic consensus Blockchain with high credibility. It can freely join or exit the network, has a fair incentive mechanism, and strong fault tolerance and high scalability, etc.
In fact, after 10 years of Bitcoin’s operation, 60% of computing power is concentrated on the top five mines, and the transaction fee has been so high that many people think that Bitcoin is a network attached to value storage, which obviously goes against the original intention of Nakamoto.
Currently, the major expansion plans on global public Blockchain market can be roughly divided into five categories: Network layer slicing technology, increasing block size of data layer and isolation witness technology, DAG technology of improving chain structure from data layer, the approaches of changing the consensus mechanism, and some offchain solutions such as crosschian, sidechain, the channels for RAS. These five expansion plans have different aims and emphases. DAG technology won people’s support with its fast response and high throughput. It is accepted by more and more Blockchain projects and become the hotspot technology in Blockchain industry. However, DAG technology also faces other problems that need to be solved, mainly about transaction consistency and miner reward problems. Therefore, many new protocols have emerged one after another for solving these problems, which are fit the spirit of Blockchain, collectively known as Block DAG technology.
The improved and optimized DAG technology greatly improves the scalability of the public chain on the premise of ensuring security and decentralization without changing the POW consensus mechanism. It should be regarded as the most ideal expansion plan in Nakamoto’s mind. Qitmeer is a new generation of Block DAG technology.
QITMEER’s BLOCK DAG technology solved scalable problem
DAG（Directed Acyclic Graph) is a data structure, which is designed to retain the advantages and improve the disadvantages of Blockchain. What is different from the chain data structure of traditional Blockchain is that DAG does not pack all data into blocks, and link blocks with other blocks. For each new data unit, it not just adds to one block in the chain, but adds to all the previous blocks, verify and confirm its parent unit and the parent unit of the parent unit, which will slowly reach the creation unit and includes the hash of its parent unit into itself. Finally, all data units are linked to each other to form a graphical structure. Therefore, the write operation of data units can realize asynchronous communication and concurrent writes, which solves the problem of high concurrency of Blockchain. The capacity of data units packed in parallel can be greatly increased, which is an innovation of Blockchain from capacity to speed.
What DAG technology solves is the contradiction between the block generation time and spread time. Because the blocks generate so fast that the forks must be increased. Forking for a long time can lead to network inconsistency. So, DAG solve the problem of forking at the end. IOTA , ByteBall & NANO are well-known projects of DAG technology at present. These projects all adopt the partial centralized consensus solution to solve the forking problem, which causes many users to misunderstand that DAG consensus can only be solved by the centralized solution.
The biggest problem of DAG technology at present is the same as multi-blocks technology and hybrid consensus technology. Because each node needs to process all transactions, it can not realize the unlimited scaling theoretically. Therefore, the premise of using DAG technology is to accept the inability to scale infinitely and the problem of duplicate transactions in blocks. It should be pointed out here that, Qitmeer didn’t mention Proof-of-Stake, it is because the bottleneck of the Blockchain scaling is not mining. POW can also achieve high throughput, PoS is more to solve the PoW problem of energy consumption.
Block DAG in a narrow sense refers to graphical ledger storage technology, just like Blockchain in a narrow sense refers to chain ledger technology, however, the broader understanding refers to the whole set of graphical ledger protocols or frameworks, just like chain-based ledger protocols or frameworks in Blockchain.
QITMEER’s POW-based Block DAG Protocol
Qitmeer technology is based on Block DAG not DAG. In fact, it emphasizes that the nodes of Block DAG are completely decentralized to join the network and get rewards. At present, only POW can do this. Therefore, Qitmeer acknowledged that the Block DAG protocols are generally based on Proof of Work (POW).
In addition, the most intuitive and the most compatible scaling solution with the classic BlockChain model, QITMEER’s Block DAG satisfies the classic Blockchain setting with the features such as freedom, fairness, strong fault tolerance and high scalability. Firstly, the network of Block DAG does not contain any special nodes, and there is no requirement for nodes to be online or not; secondly, Block DAG is a cooperative mechanism, while Blockchain is a competitive mechanism. The cooperative mechanism can avoid selfish mining to solve fairness issues.
In conclusion, Block DAG as a technology category, from GHOST protocol to the later SPECTRE, as well as the latest PHANTOM&CONFLUX are all based on the heaviest chain rules, which can achieve 50% fault tolerance comparable to Bitcoin. The application of DAG technology in BlockChain is to solve the problem of high scalability. Because the nodes of the network will store all transactions and will be limited by the network bandwidth, DAG can not achieve infinite expansion. However, for the mainstream Block DAG protocol, security has nothing to do with block generation rate, so theoretically, as long as the network and the physical performance of nodes can bear it, the block out rate can be infinitely increased.
Qitmeer network absorbs the advantages of DAG technology while mixing other cutting-edge Block DAG protocols, which are used to overcome the shortcomings of DAG and lay a solid foundation for the future commercial territory.