As I understand the Raiden network a smart contract is set up between two addresses, and loaded by each participant with tokens, and this instance of the smart contract sits in the blockchain. At this point we are all standard blockchain. Normally a write type operation in the contract would be called by creating a standard ethereum transaction targeting the contract address, and the mining process would result in the write operation being called in the contract. Again, this is all standard ethereum blockchain (as far as I know).
So my question is, what is the mechanism to call a write operation (e.g. Balance transfer) in the Raiden network? It can't go through the blockchain/miners as that would defeat the point of the Raiden network.