What are Summaries?
The essence of a Layer 2 (L2) is to enhance the scalability of the Layer 1 (L1) and increase the number of projects being built on it by securely processing transactions off the L1 chain and providing the means for these transactions to be verified independently on the L1. This process of ensuring transactions processed off the L1 main chain can be verified on the L1 main chain reinforces the security of the L2 chain. Therefore, the AvN inherits security from Ethereum via the process of checkpointing. Checkpointing is simply the process of creating epochs (periods of time that are being summarised) on the L2 and submitting a summary back to L1 about all the transactions executed within that epoch.
This logic on the Aventus L2 is contained in a pallet called “Summary.” Pallets are a specific type of Rust module from which Substrate runtimes can be constructed. The functionality and features of a blockchain’s state transition function can be modified using pallets that have their own discrete logic. One of these pallets on the AvN is called the Summary pallet.
How is Summary Pallet used on the Aventus Network?
Communication between L1 and L2 is bidirectional. Communication can start from either L1 or L2, and this is determined by the nature of the transaction. For example, token migration to L2 will always start from L1 and the publishing of Merkle root paths will begin from L2. The main design goal of every L2 solution is to provide scalability to those willing to build on L1 but find it too expensive and/or slow.
Whatever the approach may be to providing scalability, it is expected that the L2 inherits from the security of L1, i.e. although the transactions may be processed off the L1 chain, their immutability must be secured by the consensus and finality mechanisms of the L1 chain. The same applies to Aventus.
The AvN inherits security from Ethereum via the process of checkpointing handled by the Summary pallet. Every transaction executed on the AvN L2 is validated via the consensus mechanism on the chain. Periodically, the Merkle root of all the transactions executed on the AvN is calculated and the resulting root hash must be signed by ≥2/3 of the validators on the network before it can be accepted on Ethereum as valid.
This implementation of consensus is based on a ‘Plutocratic Finality’ model — collecting signatures, aka a thumbs up, from each validator on the network that the data is correct before writing it via a Merkle Root to Ethereum. Each transaction can be verified on Ethereum as the SCALE encoded transaction data for every transaction executed in that epoch is published to the smart contract on L1.
There is still yet another pallet involved in L1-L2 communication, the Ethereum Events pallet. When a transaction is executed on the contract in L1, an event is emitted. This is the primary way L1 notifies L2 of significant state changes, and the off-chain worker also has the task of listening for AvN related events from L1. These events go into a queue of unchecked events.
Queues are created for the work that is left to be done and every L2 validator will look at the queue and check if it’s their turn to do that kind of work. If it is, they will start an OCW. It runs without the restriction of the runtime.
There is a challenging period of 60 blocks during which an event can be flagged as fraudulent, and this challenge must be from over 1/3 of the votes from validators. At the end of the challenge period, the event is now ready for processing. Another off-chain worker is spun up to process and execute the event transaction.
You can find out more about the Aventus Network by reading our whitepaper here.
What are the benefits of using Summary Pallet?
At the time of implementation, only Summaries allowed for payments in native cryptocurrencies, i.e. AVT, and the use of native cryptocurrencies introduces the possibility of a staking mechanism, allowing the community (stakers) to benefit from each processed transaction.
Fewer transactions being executed on the Ethereum mainnet leads to a lower carbon footprint. Furthermore, other solutions, such as ZK rollups, require a fair bit of computational power as they are quite complex and generally time-consuming. But Summaries require significantly less computational power and can produce the Merkle root of all the transactions within that summary period (epoch) in seconds.
Each transaction is verified with the addition of a proof of stake consensus as the transactions are processed on a decentralised blockchain. This removes the possibility of a transaction being flagged in the future as fraudulent, i.e., this process does not, by default, assume all transactions are honest. This results in the publication of trustworthy summaries to L1.
What next?
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