# App Design
In this chapter you will learn how the interchain exchange module is designed. The module has order books, buy- and sell orders. First, an order book for a pair of token has to be created. After an order book exists, you can create buy and sell orders for this pair of token.
The module will make use of the Interblockchain Communication Standard IBC (opens new window). With use of the IBC, the module can create order books for tokens to have multiple blockchains interact and exchange their tokens.
You will be able to create an order book pair with one token from one blockchain and another token from another blockchain. We will call the module you create in this tutorial
Both blockchains will need to have the
ibcdex module installed and running.
When a user exchanges a token with the
ibcdex, you receive a
voucher of that token on the other blockchain.
This is similar to how a
ibc-transfer is constructed.
Since a blockchain module does not have the rights to mint new token of a blockchain into existence, the token on the target chain would be locked up and the buyer would receive a
voucher of that token.
This process can be reversed when the
voucher get burned again to unlock the original token. This will be explained throghout the tutorial in more detail.
An order book can be created for the exchange of any tokens between any pair of chains. The requirement is to have the
ibcdex module available. There can only be one order book for a pair of token at the same time.
A specific chain cannot mint new of its native token.
This module is inspired by the
ibc-transfer (opens new window) module and will have some similarities, like the
voucher creation. It will be more complex but it will display how to create:
- Several types of packets to send
- Several types of acknowledgments to treat
- Some more complex logic on how to treat a packet on receipt, on timeout and more
Assume you have two blockchains:
Mars. The native token on Venus is called
vcx, the token on Mars is
When exchanging a token from Mars to Venus, on the Venus blockchain you would end up with an IBC
voucher token with a denom that looks like
ibc/B5CB286...A7B21307F. The long string of characters after
ibc/ is a denom trace hash of a token transferred through IBC. Using the blockchain's API you can get a denom trace from that hash. Denom trace consists of a
base_denom and a
path. In our example,
base_denom will be
mcx and the
path will contain pairs of ports and channels through which the token has been transferred. For a single-hop transfer
path will look like
transfer/channel-0. Learn more about token paths in ICS 20 (opens new window).
ibc/Venus/mcx cannot be sold back using the same order book. If you want to "reverse" the exchange and receive back the Mars token, a new order book
mcx needs to be created.
# Order books
As a typical exchange, a new pair implies the creation of an order book with orders to sell
MCX or orders to buy
VCX. Here, you have two chains and this data-structure must be split between
Users from chain
Mars will sell
MCX and users from chain
Venus will buy
MCX. Therefore, we represent all orders to sell
MCX on chain
Mars and all the orders to buy
MCX on chain
In this example blockchain
Mars holds the sell oders and blockchain
Venus holds the buy orders.
# Exchanging tokens back
ibc-transfer each blockchain keep a trace of the token voucher created on the other blockchain.
If a blockchain
ibc/Venus/mcx is minted on
Venus then, if
ibc/Venus/mcx is sold back on
Mars the token unlocked and received will be
The features supported by the module are:
- Creating an exchange order book for a token pair between two chains
- Send sell orders on source chain
- Send buy orders on target chain
- Cancel sell or buy orders