Routing With Built-In Token Swaps
Buyers and sellers usually each have a preferred currency/token. When both parties prefer different tokens, one party has to accept dealing with a non-preferred token. In addition to being inconvenient, this can also require open a new channel, this making the payment slow and expensive. Dealing with a different token might not even be possible for some parties (e.g. due to bookkeeping restrictions). If the Raiden Network provided a way to swap tokens while doing the payment, both parties could deal with their preferred token and transaction would be quick, cheap and convenient.
Node A wants to pay node B an amount of 10 T2 tokens, but A only has T1 tokens. Node A requests a route from the PFS:
source: A target: B target_amount: 10 T2 source_token: T1
The PFS looks for a route that minimizes the amount of T1 tokens that A has to spend in order for B to receive 10 T2, taking into account both mediation fees and the required token swap. The returned route might look like
T1 T1 T2 A --> M1 --> M2 --> B
meaning that mediator M2 accepts T1 and sends T2, thereby providing both mediation and token conversion. Despite using different token networks, the payment will still be atomic by using the same hash time lock across the whole path.
Nodes willing to do token swaps have to tell the PFS their exchange rate. Broadcasting could be much traffic, polling would slow down routing.
The PFS has to be able to route through multiple token networks at the same time.
Behavior not clear for non-strict routing
The route can fail due to changes in conversion rate. This can be mitigated by adding some safety margin, but this increases the price for the sender.