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Cross-Chain Transfer Protocol (CTP)

Analogous to the application-level protocols Hypertext Transfer Protocol and File Transfer, Axelar’s application-level protocol stack CTP sits on top of the routing protocols (such as the CGP)

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Axelar’s Core Protocols

The Second Central Element of Axelar’s Protocol Suite is the Cross-Chain Transfer Protocol (CTP)

CTP

Cross-Chain Transfer Protocol

Analogous to the application-level protocols Hypertext Transfer Protocol and File Transfer, Axelar’s application-level protocol stack CTP sits on top of the routing protocols (such as CGP). Developers can use the Cross-Chain Transfer Protocol to perform cross-chain requests to any blockchain but also to lock, unlock, and transfer assets between addresses on different blockchain platforms.

The Cross-Chain Transfer Protocol (CTP) can be used by developers to perform cross-chain requests:

Developer Blockchain 1

Request

CTP

Blockchain 2

CTP can also be used by developers to execute cross-chain application triggers. This is for instance the case when if dApp 1 on chain A updates its state if dApp 2 on chain B meets a specific criteria (example: interest rate < x%). Similarly, developers can utilize CTP to perform cross-chain requests between apps located on different chains. An example for this would be that a smart contract on chain A can update the smart contract on chain B.

End users can use CTP to access and interact with the application of their choice on any chain via simple API calls (analogous to HTTP GET/POST requests).

In short, CTP enables the composability of programs across blockchain platforms.

Axelar’s application-level protocol

CTP in Detail

The Cross-Chain Transfer Protocol enables applications to seamlessly leverage cross-chain features. Its functionality is especially useful for asset transfer features as used in DeFi dApps. Such applications typically consist of a front-end GUI, smart contracts, and an intermediary node posting transactions between front-end and smart contracts.

Applications can utilize Axelar’s cross-chain features by calling CTP queries. The process is analogous to HTTP/HTTPS GET/POST methods. Subsequently, the requests are picked up by the CGP layer, executed and returned back to the users.

Let’s have a look at the functionality CTP provides:

CTP Queries

CTP enables developers to host their apps on any chain and integrate the app’s smart contracts with threshold bridge accounts to execute CTP queries

Threshold bridge accounts

Developers building their contracts on a given chain can reference threshold bridge contracts to obtain cross-chain support. Doing so enables applications to do the following:

  • Registering a blockchain the app needs to communicate with
  • Registering assets on a blockchain the app would like to leverage
  • Perform asset operations, such as accepting deposits, processing withdrawals, and other functions similar to ERC-20 contract calls

Additional Cross-Chain Requests

The following more general cross-chain requests between applications across blockchains are supported by CTP as well:

  • Performing Public Key Name Services: mapping public keys to phone numbers /Twitter handles through a universal directory
  • Cross-chain application triggers: updating the state of an application on chain A if another application on chain B satisfies a given criteria
  • Smart contract composability: updating the state of smart contract on chain A based on state of contracts on chain B

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