A transaction between two channels will have two sets of channel definitions with two distinct rating IDs. The two rating IDs are fed into a rule engine inside the sender zone, which then calculates the fee owed, as well as who owes it. It is possible to attribute the entire fee to sender, or the recipient, or to split it between the two. It is also possible to monetize by a fixed fee charged "per use", or by commission, or even via a flat fee for a given period of time. It is also possible to have a completely free channel.