March 21, 2023

This post was originally published on Ankr

A trustless bridge framework for creating interoperable app-specific blockchains on BAS and beyond.

Application-specific blockchains (app chains) have been the most interesting and promising scaling solution of 2022, with many wondering if they are the final puzzle piece needed to have extremely scalable web3 applications. Currently, app-specific chains are possible to build on ecosystems like:

  • BNB Application Sidechains (BAS)
  • Polygon Supernets
  • Avalanche Subnets

Ankr is currently helping Web3 projects build app chains on any one of these ecosystems with our end-to-end Ankr App Chains service. But more than that, we are helping blockchains like the BNB Smart Chain, Avalanche, Polygon, and others architect their app chain (sidechain) frameworks for the most high-performance solution for scaling possible.

Ankr is uniquely positioned to help build and bring new app chains to market due to our involvement in engineering the framework for them. Earlier this year, Ankr worked closely with the BNB Smart Chain team to release the first BNB Smart Chain Application Sidechain (BAS) testnet that led the way for the mainnet launch, which is bringing several advantages to the ecosystem.

BAS & Other App Chain Ecosystem Advantages


App chains can process more transactions faster and more affordably than congested Layer-1 blockchains as they have dedicated resources serving only one app. On a BAS chain serving just one application, users’ transactions are served by a dedicated virtual machine and set of validators.

Highly Customizable

When building an app chain, developers can choose which programming languages, consensus mechanisms, and development frameworks they want to use. They can customize, tweak, and add features like more security, custom cryptography, and much more.

Improved Web3 User Experiences (UX)

As app chain developers can create blockchains with extremely low (or even zero) gas fees with fast transactions, that means the users of their app get a much better experience.

The Missing Piece? Interoperability

App chains are one of the best solutions for scalability on highly adopted developer ecosystems like Polygon and the BNB Smart Chain, but they need to be able to communicate with each other seamlessly for a better user experience. Users need to be able to transact across multiple different blockchains and applications to mold Web3 into a more holistic and less isolated experience.

Ecosystems like Cosmos and Polkadot have been exploring interoperability possibilities as early as 2016. Interoperability is the core idea behind combining the capabilities of all “networks” into an “internet” with much better ease of use and a less isolated user base. Hence, the “internet of blockchains” described in their marketing.

However, with BAS Relay Hub, app-specific blockchains can now implement the interoperability advantages of ecosystems like Cosmos and impart them directly into EVM-compatible environments like BNB Smart Chain. The end result will be a new standard for blockchain that will allow much greater collaboration, interoperability, and scalability that will give Web3 the necessary user experience improvement needed for adoption on a massive scale.

What is BAS Relay Hub? A solution for app chain interoperability via bridging

BAS Relay Hub is Ankr’s solution designed to act as a trustless bridge that connects all BNB Application Sidechains (BAS) with each other and with other chains like the BNB Smart Chain and Polygon, Ethereum, and more.

BAS Relay Hub was created using the same codebase that Ankr made for our audited and secure DeFi bridge. This bridge is capable of transferring liquid-staked assets to and from blockchains like Ethereum, Polygon, and the BNB Smart Chain. It was a relatively simple solution to adapt this bridge to allow not only transfers among layer-1 blockchains but all app chains within BAS as well.

How Does BAS Relay Hub Work?

Technically, BAS Relay Hub is a smart contract designed to provide seamless interchain communication between all BAS chains for enhanced interoperability. The BAS Relay Hub is comprised of trustless “relayer” nodes that verify the transition of assets between chains using confirmations from validators to reach a consensus. To confirm the status of transactions, the Relay Hub will check for data that affirms the original chain has deposited and locked the assets to the smart contract so the new chain is able to mint the new tokens by verifying the information that should currently be populated, such as:

  • Wallet balances
  • Signatures from validators
  • Block headers
  • Storage slots
  • Receipts
  • Logs

Relayer nodes on BAS Relay Hub search for all this information by synchronizing the data from all blockchains since their genesis blocks and scouring it for pertinent data to confirm cross-chain transactions.

Caption: BAS app chains connect to the Hub composed of relayer nodes and transact among each other securely.

The Relay Hub In Use

App chain users will interact with the BAS Relay Hub bridge whenever they want to send assets off of their app chain or receive assets from outside of the app chain. Here is one example of what this process could look like:

Example: A player of a game running on BAS wants to deploy their assets on a new Decentralized Exchange that supports them on another BAS chain. The user wants to add some tokens they gathered in the game to the DEX in a new liquidity pool to earn rewards.

  1. They will first need to go to the BAS Relay Hub tool within Ankr’s Chainscanner platform (in progress) and connect their wallet, such as MetaMask. They will then need to select the chain they are sending from, the desired destination chain, and the amount of the asset they would like to bridge. They will then deposit and “lock” this amount in the bridge’s smart contract.
  2. When the user confirms the transaction, the mining process will begin for the relayer nodes working in the background. The relayers will collect confirmations from validator nodes in order to create a “proof.” This proof will provide the authentication needed to remove (burn) funds from the original chain to mint them on the new chain.
  3. Once enough confirmations have been discovered (from 75% of the validators), the user will then be able to claim their tokens on the new network. The user will do this by switching the network on their wallet when prompted by the application and selecting “confirm.”

The transaction will now be fully bridged and complete. The process should only take a few moments and requires a small gas fee for the transaction.

What Is Next With Relay Hub?

The BAS Beacon Chain

Additionally, in the research and development stage for BAS, Ankr’s engineering team is working on a Beacon chain that will be responsible for the synchronization of blocks from all BAS chains. The Beacon chain will manage all assets and funds, and all BAS chains will work as collators to collect and share their data with the beacon — very similar to the methods used in ecosystems like Polkadot. The end result of the beacon chain will be extremely fast and affordable (near-zero fee) transactions between all BAS chains.

Relay Hubs For All App Chain Ecosystems

Once Ankr’s engineering team completes the solution for BAS Relay Hub, they will begin to apply the solution to other app chain ecosystems like Polygon Edge Supernets and Avalanche Subnets. This will likely become the new standard for interoperability among application-specific blockchains on the way to a truly connected Web3.

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Introducing BNB Application Sidechains Relay Hub was originally published in Ankr on Medium, where people are continuing the conversation by highlighting and responding to this story.

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