First of all I want to thank Prof. @alphafx for this wonderful lectures. It was very Educating and I must say I learnt alot of new crypto concepts.

Now to the lectures proper.

              QUESTION

Write on any of these consensus algorithms extensively

I Choose to write on Stellar Consensus Protocol

My Topic Sub-headings:

• What is Consensus Algorithms
• About Stellar Payment Network
• Stellar Consensus Protocol explained
• SCP vs POW
• SCP vs DPOS
• Advantages of SCP
• Disadvantages of SCP
• Conclusion

What is Consensus Algorithms.

Consensus meaning coming together or agreeing by a set so to come to a particular conclusion. and
Algorithm meaning a sequence of well defined finite or logical terms designed basically for the purpose of solving problems on an electronic system.

Therefore, a Consensus Algorithm means an assembly of this sequence of well defined datas or logical terms so to maintain the activities of a block chain. Thereby the monitoring of transactions, carrying out of specific task by members of a block chain is aided by the consensus algorithm.

About Stellar Payment Network.

This is a digital platform that makes payment of specific digital currencies possible. Now in the real world banking system, transfer of real currency's ecspecially between country's becomes slow and the charges are always mind blowing, now this is were stellar comes in to provide a safe, secure and less-charge transfer of token and digital currencies between country's, companies and individuals in seconds.

Now another interesting thing about the stellar Payment Network is it's ability to collect or accept digital tokens specially designed by a company to act as a replacement or collateral of a real world currency, Usually called an Anchor token. For example. A company can decide to make payment for an acquired item and it decides to use the stellar Payment platform, so it will have to replace it's real world dollar with an anchor dollar designed by the company in the stellar platform.
An advantage of doing this is that it will reduce the transaction charges and even faster which would have been incured by transacting the real dollar.

Stellar also allows for a transaction between currencies of unlike values within seconds like dollar and pero or naira. And it gives opportunity to a crypto token which is the Bitcoin token.

Stellar Payment Platform is able to carry out all this critical task without failure, stuck or blockage of transactions on the platform by using a Byzantine agreement protocol called SCP (Stellar Consensus Protocol).

This leads us to our next sub-head.

Stellar Consensus Protocol Explained

SCP was first described in a whitepaper by David Mazières in 2015.
Now before I dive into explaining the Stellar Consensus Protocol proper, which is a very complex principle from stellar Whitepaper, I'll be explaining SCP generally in real life situation to aid understanding, before I proceed to the complex explanation.

Assuming a company of 6 persons has a need of someone who will be making a financial report of the association to the highest authority and it is clearly certain that all the 6 personels can't be the ones making the report. So there is a need for a representative.

But then the representative fails to make the report on time and decides to joke with the opportunity. Another member is choosen who repeats the same process of untrust.

Then the members decide to cast a vote to elect a more serious leader to carry out the task, but the problem is who gets to control the ballot, will the person be trusted. Okay now what if the members get to decide on the controller on the votes to be casted, another question arise of the persons availability during election.

So this problem of trust, during an agreement from nodes(members) from quorums making up the blockchain is what the SCP seeks to solve.

Now the SCP works with the principle of Voting, Accepting and Confirmation.

Now the principle that allows this happens is the principle of Federated Voting.

Federated Voting

Now the federated voting is a System incurred to know if every node of the group will accept a normination or proposal.
Now this is done by nodes making multiple normination of particular value and watching it go through a series of acceptance and rejection by other nodes in a quorum.

A complete round of Federated vote cannot be successful without other node within a quorum getting to accept the normination of the previous or say first node normination.

Now there are other nodes within a quorum that might reject the normination of the first node, so to solve this problem there is a pre-arrangement of quorum slice. Because for a vote of value to be passed as accepted, majority or supermajority say 2/3 of a quorum must accept the normination. So within a quorum there are smaller quorums called quorum slice to help identify the nodes standing for or against a particular vote or nomination, it helps take decision for the quorum to follow.

Therefore in an SCP, it is made up of so many quorums formed by multiple quorum slice and a federated vote has to be passed through this quorums and the majority of the nodes in each quorums must accept the normination for the vote to be approved by the SCP.

Voting, Accepting and Confirmation

Now this is the main process of federated voting which subsiquently leads to SCP completion process.

Now at first there is a normination from a node in a quorum. And N node norminate's or votes for say value (V). So immediately there is a broadcast carried out across the quorum that N node norminate's (V). A node in a quorum slice then received such broadcast then makes a look out to see if other nodes in the quorum outside it quorum slice has accepted the normination, if convinced enough the node also nominates it and subsequently accept.

Now Voting a value V which means, I will never reject value V does not mean that the receiving node will not norminate or vote another value but that it can't vote against it. Now the node goes on to accept the vote. This is a even more stronger progress to further confirm the nodes stands in the quorum.

So by multiple nodes within the quorum accepting the same normation of V and you also have to understand that due to the open endedness of the federated voting process and multiple quorum slice available, it is difficult to trick the whole quorum to accepting a vote against their will. So after accepting the N by multiple nodes from multiple quorum slice by seeing majority of the N in other quorum accepting it accepts and has no choice but to commit and accept. .

At this point a complete federated voting is attained. A multiple/Continues attempt of the process is what approves or makes up the Stellar Consensus Protocol.

So what if the Federated Voting process experiences failure, that's were the protocol is useful.
The node in a quorum cast a ballot of N=2f+1 which gives the system a finite repetition of the whole process in case of N failure.

Therefore a Stellar Consensus Protocol is a successful multiple rounds of federated voting. And this process is carried out within 5 seconds. Whereby to reach a consensus they must provide safety and liveness which is enwrapped in the process afore-explained.

SCP vs Proof of Work

SCP	PoW
Faster transaction confirmation	Slower transaction confirmation.
Anchor dollars, pero dollars (called on-chain tokens)	Bitcoin, doge, litecoin, menero.

SCP vs Delegated Proof of Stake

SCP	DPoS
Low transaction charges	High transaction charge.
Easy tracing of malicious activities	Easy disorganisation of blockchain content, through malicious activities.
On-chain tokens	Tron, Ark, Tezos.

Advantages of SCP

• fast transaction which is within 5 seconds.
• difficulty of transaction failure because of the Byzantine agreement protocol.
• Easy tracking of transaction history.
• Difficulty in carry out a fake transaction because of the large quorum size.

Disadvantages of SCP

• Limitation in currency traded like the most altcoins.
• Needs more message for a transaction to pull through.
• Government policy of unacceptability of customised on-chain token might be a limitation for Stellar transactions in some locations.

Conclusion

Stellar Consensus Protocol seeks to help in the minimization of the difficulties faced in transaction of real currency's or tokens. Such as slow transaction, counterfeit transaction and untraceable transaction history.

Thank you.