# Overview¶

## What is CPChain¶

CPChain is a new blockchain infrastructure for the next generation IoT.

## Built-in Smart Contract¶

CPChain comes with 5 built-in smart contracts to ensure normal operations of DPoR. Other contract files in out code repository are either abandoned or not yet activated. Due to the lack of space in this page, we explicate all five smart contracts in Built-in Smart Contract.

## Private Contract¶

Our data privacy mechanism allows users to deploy and call private contract on cpchain for completing their private transactions in a secure way. Besides the agent P (validator and intermediary) and accounts accepted by the deployer, others are permitted from viewing the private transactions. Although the private transactions are invisible for others who are not the transaction’s participants, some sophisticated key data is recorded and maintained in blockchain. The data is available for audition and validation for private transactions when necessary.

### User Scenario Steps¶

1. Seller A registers an item via the private contract CT. An item includes name, ipfs_cid, price, description and so on.
2. Buyer B checks the registered items on contract CT and chooses some items to buy.
3. Buyer B pays money to an escrow contract CE.
4. Buyer B sends contract CT an order describing which item to buy and its public key, the one used to encrypt the item’s symmetric key (e.g. AES).
5. Seller A receives the notification about the order from contract CT, and checks if the buyer have enough money from the escrow contract CE.
6. Seller A sends contract CT the confirmation message attached with the symmetric key encrypted by the buyer’s public key.
7. Buyer B receives the encrypted symmetric key, and then decrypts it. With the symmetric key, the buyer B can decrypt the data on IPFS and then confirm whether it is what it needs.
8. The agent P notices the confirmation and transfer money to seller A.

## Consensus¶

The consensus in LBFT 2.0 is determined by two committees: Validators Committee and Proposers Committee, which together lead to a bipartite committee structure. Proposers and validators, just as their names imply, take the responsibility of proposing and validating blocks respectively.

The consensus process works in a finite state machine which consists of five states idle, prepare, commit, impeach prepare and impeach commit. The former three states are designed for normal cases, and the rest, named as impeachment, are specializing in handling abnormal cases.

Due to the lack of space in this page, we explicate LBFT 2.0 in Consensus.

## CPChain Ecosystem¶

### CPChain Nodes Roles and Pools¶

Economy Node: Requires a minimum of 20,000 CPC tokens deposited in Economy Pool for participation. Investors who meet this requirement may participate as an economy node and have the right to vote in the community.

Reputation Node: Requires a minimum of 200,000 CPC tokens deposited in RNode Pool for participation. Investors with the basic configuration of computing and storage can participate to support the CPChain Open Transmission Protocol (COTP).

Industry Node: IoT Industry partners and CPChain ecosystem’s peer developers have the right to participate as an Industry Node.

Note that there are two separate pools for deposit.

Economy Pool: Any node deposit at least 20,000 CPC tokens in this pool is qualified as an economy node.

RNode Pool: Any node deposit at least 200,000 CPC tokens in this pool is qualified as an RNode.

### Reputation Nodes¶

A node has to meet one of the following requirements to become a Reputation Node:

1. At least 200,000 CPC in RNode Pool + Computing and Storage node: A node must lock-up a specific amount of tokens (200,000 minimum and 5,000,000 maximum) for 90 days and must satisfy the software, hardware, and network connection requirements. The locked up tokens have a positive correlation with the basic rewards. Reputation nodes will be refunded after they leave the election.

2. Industry Node + Computing and Storage Node: An industry node will be upgraded to a reputation node once meeting all the hardware, software, and network requirements. Industry nodes must be verified by the CPChain foundation.

Reputation Nodes have the right to be elected as a proposers committee member and to be granted rewards from the Blockchain.

### RPT Evaluation¶

RPT (abbreviated from reputation) value of a node is evaluated by extracting data from blockchain. By employing RPT Contract, a node can evaluates its RPT value by following five dimensions:

• Account Balance（AB),
• Transaction (TX),
• Data Contribution (DC),
• Blockchain Maintenance (BM),
• Proxy Reputation (PR).

Each dimension has a full score of 100 point. And the total score is calculated as:

$$RPT = 50\times AB + 15\times TX + 10\times PR + 15\times DC + 10\times BM$$,

which leads to 10,000 full score of RPT.

Note

All scores for each dimension are evaluated within to a time window, which is latest 100 blocks. Data outside this window are no longer taken into consideration.

Unless otherwise stated, the score for each dimension is calculated by the same methodology. In total, there are at most 100 RNodes in each term campaign. The RNode with $$i$$-th highest RPT will get $$(100-i+1)$$ score.

#### Account Balance¶

A account balance score is granted to an RNode according to its account balance ranking among all RNode addresses (excluding CPChain Foundation and Exchange addresses).

#### Transaction¶

Transactions here include all transactions sent by a given user. The definition of transactions can be expanded as the of CPChain ecosystem develops.

TX score is evaluated by all transactions statistics. The distribution of transactions can follow a long tail distribution or power laws.

#### Proxy Reputation¶

An RNode can serve as a proxy helping other nodes complete transactions. Its RPT is augmented after assuming the responsibility as a proxy.

Proxy reputation score is calculated according to following rules:

1. Once an RNode registers as a proxy, it obtains 10 initial points.
2. For each successful transaction with the node’s help as a proxy, it gets 5 points.
3. The full score is 100 points.

#### Data Contribution¶

Uploading data augments RPT value. There are two parts in data contribution, as basic DC score and bonus DC score.

Data contribution score is calculated according to following rules:

1. For each file an RNode uploads, the node is rewarded 3 points in DC score.
2. The full score of basic DC is 30 points.
3. Each time other node purchases a file that RNode uploads, the RNode is rewarded 5 bonus points.
4. The full score of bonus DC is 70 points.

#### Blockchain Maintenance¶

Blockchain Maintenance score is calculated given a node’s contribution in proposing a certain block.

### Node Entitlements & Rewards¶

CPChain’s ecosystem is established by a lot of Internet of Things (IoT) enterprises, developers and users. It is a long-term process. As a result, CPChain will divide the incentive system into two stages. In the first stage, CPChain Foundation would be the main fund provider, for the ecosystem establishment and the chain maintenance. The next stage is mainly performed by the market. With the optimization of CPChain ecosystem and the increase in data sharing and transferring, the reward for RNodes will mainly be generated by smart contracts and market transactions.

In the first stage, reputation nodes’ entitlements will be allocated to two parts:

#### Basic Rewards¶

CPChain will create a reward pool with 5 million CPC annually (1.25 million CPC quarterly, 13,700 CPC daily). The Economy Nodes receive the corresponding CPC reward based on the ratio of the locked margin to the total margin. (Economy Node needs a 90-day lock-up session). The detailed process goes as follows:

Each season lasts for 90 days, including the first 3 days for the raising period, the 86 days for the lock-up period, and the last 3 days for the settlement period. There is no overlap between each period, and the second period can only be opened after the end of the first period. Each period does not overlap with other one. And the contract is always at a certain period, the raise period, the lock period or the settlement period. In the raise period, you can deposit tokens into the economic pool or withdraw the tokens. No operation is permitted during the lock period. And interest for each season can be taken away during the settlement period. If the user does not take the interest, the administrator will assign them one by one.

In raising, the following operations are allowed:

1. All civilians can deposit coin in the reward pool, to become Economy Nodes.
2. Nodes that have already had coins deposited in the pool can choose to
1. whether continue deposit the next season
2. or renew the deposit value.
3. For a node determines to withdraw deposit, it needs to call withdraw function on their own initiative after lock-up period finishes.

In settlement, the following rules are applied:

1. No one adjusts or withdraw its deposit until next fundraising.
2. Nodes can collect interest of this season.
3. Interest that do not proactively collected by its owner will be allotted to the owner by admins.

Interested reader can refer to Reward Smart Contract to check detailed smart contract implementation.

The reward for a certain node from the pool is proportional to its deposit in a season. In other word, the basic reward is calculated as $$5000000 \cdot d/D$$, where $$d$$ is deposit of a certain node, and $$D$$ is the total value of coins in the reward pool.

#### Maintenance Reward¶

Proposers committee nodes are entitled to blockchain maintenance rewards, after it proposes a block and successfully gets it inserted into the chain. As defined in the RNode ecosystem, the annual supply from maintenance is 40 million CPC in the first year, and being decreased by 25% annually for the next four years. Thus, the annual supply for five years is 40 million, 30 million, 22.5 million, 17 million and 12.75 million respectively. After five years, the supply runs out. In other words, no CPC is rewarded after that time.

Meanwhile, CPC Mainnet inserts a block every 10 seconds, which yields around 3 million blocks each year. Therefore, we conclude the reward and supply in the table below.

Year Reward Num of Blocks Supply
1 12.65 3,162,240* 40,002,336
2 9.51 3,153,600 29,990,736
3 7.13 3,153,600 22,485,168
4 5.39 3,153,600 16,997,904
5 4.03 3,162,240* 12,743,827.2

* Both the first and the fifth year contain a leap day (29 Feb 2020 and 2024, respectively), which results in a larger number of generated blocks compared to the other three years.

Note that in our LBFT 2.0 protocol, an impeach block in inserted into the chain if the proposer is faulty or non-responding. Intuitively, a faulty proposer cannot receive the reward. Hence, the amount of annual supply could be smaller than the one listed in the table above.

### Lock Deposit¶

Use smart contracts to lock deposit, the functions are as follow:

Determine the node level based on the amount of deposit of the node. lock the deposit to fixed range of length of blockchain. Reward distribution according to proportion of node’s deposits. Connection with Reputation list.

## Hardware Specification¶

### Minimum Requirement¶

• Memory: 4GB
• Storage: 100GB
• CPU: Intel Xeon E5-1650 v3 (alike)
• Network: 300Mbps

Note

Some operation systems may have system processes with very large space or computing overheads running in background. An example is tracker-store in CentOS, which may cause up to 100% CPU load.

Beware of these kind of processes if you encounter an unexpected killing of cpchain by the operation system, especially the one due to out of memory (OOM) error.

### Example Configurations for Proposers¶

Cloud servers (like Microsoft Azure or Amazon Web Service) of monthly cost at around 50 dollars suffice to become an RNode.

Basic VPS configurations:

• Amazon Web Service t2.medium
• 4GB memory, 2 vCPU, located in Singapore.
• $0.0584 per hour pay as you go. •$0.03504 per hour pay one year reserved.
• Microsoft Azure B2S
• 4GB memory, 2 vCPU, located in Singapore.
• $0.0528 per hour pay as you go. •$0.0309 per hour one year reserved.

Better computing capability configurations:

These severs are equipped with Xeon Processors.

• Amazon Web Service c5.large
• 4GB memory, 2 vCPU, in Singapore.
• $0.098 per hour pay as you go. •$0.0588 per hour one year reserved.
• Microsoft Azure F2s v2
• 4GB memory, 2 vCPU, in Singapore.
• $0.098 per hour pay as you go. •$0.0736 per hour one year reserved.

### Civilian Requirement¶

For normal civilians, a lower end of setup may also suffice. Our experiments show that a server with 2GB memory can work normally for at least thousands of blocks. But one requirement is that there are no other space-consuming processes competing with cpchain for space resources.

And usually a user run a civilian node to invoke APIs. Some APIs have higher space and computing overheads like Cpc.getRNodes. We recommend you to use a machine with memory of at least 3GB as a civilian.

## Execution Fee - Gas System¶

All operations in CPC is not conducted free. An amount of tokens are cost as operation fees, whose unit is denoted by Gas. Gas is measured by the amount of computational overheads when executing a certain operation. Every single operation, no matter transaction or smart contract, is executed along with gas deducted.

Here we list important definitions:

1. Gas, the unit measuring execution fee.
2. Gas Limit, the maximum gas the applicant willing to pay.
3. Gas price, the amount the applicant pays for each unit of gas.

### Gas¶

Gas is a special unit, measuring the amount of computational overheads when executing a certain operation. Every operation is associated with an fixed number of gas, indicating the computational effort of this operation.

All gas-consuming operations are curated in configs/protocol_params.go. An instance is shown below, demonstrating the value of gas of a non-smart-contract transaction and creating a smart contract.

// Per transaction not creating a contract.
// NOTE: Not payable on data of calls between transactions.
TxGas                 uint64 = 21000
// Per transaction that creates a contract.
// NOTE: Not payable on data of calls between transactions.
TxGasContractCreation uint64 = 53000


Thus, a normal transaction requires 21,000 gas, while a smart contract is created at a cost of 53000 gas.

### Gas Limit¶

Gas limit, as its name indicates, refers to the maximum gas a node is going to pay in a transaction. Apparently, the equation $$gas \leq gasLimit$$ always holds. It limits the upper bound of transaction fees in a contract, and avoid a contract involving unexpectedly high gas. This kind of situation occurs when an error, like too much loops, is embedded in the contract.

Gas limit is tunable parameter when a node applies for a transaction. We also offer a default setting for it, preventing the node from being drained out.

### Gas Price¶

Gas price is the fee for each gas a node pays. By analogy, gas is like gallon when fueling a car. Gas limit is the fuel tank of the car, limiting maximum gas. And gas price is the petroleum price per gallon. Thus, the total fee for a transaction is $$gas \times gasPrice$$.

When a node applies for a transaction, the system calculates a gas price based on transaction history on the chain. However, gas price is also tunable. A node can define gas price at any value as long as it can afford it. Transactions with high gas price have higher chance being selected by committee, and further get inserted into the chain. But it expenses more for the node. In comparison, a low gas price demands low cost of tokens, by sacrificing the possibility of being verified by committee.

### Fee Calculation¶

The fee of a certain transaction is $$gas \times gasPrice$$. However, for smart contract transaction involving multiple operations, fee cannot be determined until the whole transaction terminates. Thus, when a node applies for a transaction, it is required to pay $$gasLimit \times gasPrice$$ tokens. And after the transaction terminates, unused fee $$(gasLimit-gas) \times gasPrice$$ is refunded to this node.

Note that transaction fee as $$gas \times gasPrice$$ is not refundable. Even the transaction fails, like an abnormal contract involving gas outnumbering gas limit, the system does not refunds deducted fee. The rationale is that committee members have assumed their responsibility of verifying this transaction at the cost of their computing overheads, which should be rewarded with transaction fee. In addition, this mechanism avoids malicious nodes occupying computing capability of the chain at no cost.