Ethereum's raiden network can achieve market speed while maintaining the property that an exchange happens or it doesn't (a single transaction can contain the t

Ethereum's raiden network can achieve market speed while maintaining the property that an exchange happens or it doesn't (a single transaction can contain the transfer of both assets being exchanged) the way it works is that transactions are made but not immediately submitted to the blockchain. If a new transaction happens it is designed so that the later transaction if submitted prevents or even undoes all previous transactions on the same channel. Combine that with funds held in escrow (on chain) and a challenge period and you have a way to transfer funds back and forth at communication speed rather than blockchain speed and if there is a dispute or the trading parties wish to go their separate ways everything becomes finalized to the chain. In this model there would be the equivalent of brokers. These are parties who are willing to act as nodes in a network of buyers and sellers. These brokers do not take ownership of user funds though. They do have the ability to refuse to act as a relay for whoever they want to refuse but they don't have the ability to confiscate funds, do fractional accounting or prevent users from using another note to rout their transactions through. These entities could also be anonymous because there is no need to trust them but they could also be identified and only relay transactions for KYC compliant users.