# Reverse Gas Model

IC’s[ reverse gas model](https://internetcomputer.org/capabilities/reverse-gas) (users don't need to pay gas fees to interact with smart contracts, whether reading or writing) significantly benefits Omnity. It allows us, the protocol designers, to eliminate off-chain relayers. The user's front end takes the first half of the relayer’s work, relaying cross-chain messages from the source chain to IC. 

Omnity has the privilege to choose this design because of IC’s reverse gas model; otherwise, all cross-chain users would be required to install an IC wallet and hold $ICP beforehand, significantly narrowing Omnity's applicability.

For cross-chain connections with sparse traffic, user relaying may not update the consensus state on Route canisters on time. In that case, Route canisters can fetch consensus states from respective blockchains directly via [HTTPS Outcalls](https://internetcomputer.org/https-outcalls), presenting a brand new paradigm that should be called on-chain relayer, which, once again, is not feasible on other blockchains except IC. The on-chain relayer doesn’t stop at syncing source chain block headers. It‘s also responsible for sending cross-chain messages to the destination chain (which is the second half of the relaying work that used to be done by off-chain relayers).


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