Gas Token as fee for AMB transactions

As part of our recent activities related to improvements related to the bridge contracts we introduced the support of Gas Token minting on Arbitrary Message Bridge for transactions directed from Ethereum Mainnet to a side chain.

The idea is to collect fees in form of Gas Token ( for transactions an AMB relays from one chain to another. It means that for every transaction requesting to pass data through the bridge, the contract will mint some fixed number of Gas Tokens.

Here is intuition:

  • Fee: 0.8 Gas Tokens (for example)
  • Gas price: 5 GWei/gas
  • Ether price: 130 USD/ether
  • Since the operation to mint 0.8 Gas Tokens will consume ~3000000 gas, the fee collected by the bridge is equal 3000000 gas * 5 GWei/gas * 130 USD/ether = 1.95 USD.

Currently, the Kovan-Sokol AMB bridge (the contract on the side of the Kovan testnet) has been upgraded with the new implementation as so every application could test impact of increased gas consumption. Here is a transaction demonstrating the process of Gas Tokens minting:

Our plan is to upgrade is to upgrade ETH-xDai AMB and ETH-POA AMB on the 11th of April. Starting from that date all transaction directed from the Ethereum Mainnet through the Arbitrary Message Bridge will consume more gas to collect fees.

More information about Gas Token introduction to AMB and ways how to reduce number of gas consumed by transaction going through the bridge can be found in the TokenBridge documentation.