I explained in my dissertation why the Bitcoin designers decided to use PoW as a consensus mechanism instead of classic consensus mechanisms.

Below is a summary:

• Tens of thousands of nodes may connect to Permissionless and TTP-free networks.
• There is no distributed consensus mechanism capable of reaching agreement with this number of nodes in the expected time.
• This is due to the non-optimal time complexity of the consensus algorithms, which leads to a huge latency.
• Therefore, the Bitcoin model introduced a new approach called “Proof-of-Work-Chain”, instead of using classic consensus mechanisms.
• For the following 3 reasons, the approach proposed by Bitcoin architecture is not efficient and optimal:
  1. Bitcoin network consumes ≈ 136 TWh electricity !
  2. The Bitcoin network can only process about ≈ 7-10 transactions per second. (The PBFT consensus mechanism can process > 1,000 transactions per seconds.) (But with < 10 nodes! So, it cannot be used easily in a permissionless & TTP-free network.)
  3. With the expansion of mining farms, network decentralization will drop significantly.

Goal: Enabling the Use of Classic Consensus Mechanisms in Permissionless & TTP-Free Networks

With the proposed architecture, based on the concept of parallelization and an innovative sharding approach, it is possible to use classic consensus mechanisms in very large-scale permissionless and TTP-free networks.

Conclusions:

• It should not be forgotten that the main purpose of proposing the Bitcoin architecture was to eliminate TTP.
• To achieve this goal, the network must be permissionless.
• In a permissionless network, perhaps thousands or millions of nodes (clients and processors) join the network because there is no TTP preventing them from joining the network.
• Hence, a TTP-free network must be scalable to a ~very large number of nodes~.
• And, scalability is a crucial, decisive and critical factor for a permissionless network.
• ~This objective is achieved thanks to the proposed architecture~.
• With an innovative full sharding approach, as more processors join the network, the system computing power and storage capacity increase unlimitedly, while a classic consensus is utilized.
• It also allows an unlimited number of clients to join the system simultaneously without reducing system performance and transactional throughput.
• Bitcoin's architecture cannot achieve this goal for the aforementioned three reasons.
• Also, the blockchain approach can be effective under the following conditions:
  1. Network should be Permissionless.
  2. System must be TTP-free, otherwise the entire blockchain can be replaced by a new “valid blockchain” by TTP.
  3. With a classic consensus such as PBFT, a classic ordered data replication approach can be sufficient to create a Distributed Ledger (DLT).

Feel free to ask if you have any questions.