What is the flow for price quotes/exchange rates when making payments over Interledger?

[sappenin]

@emschwartz

If you want to figure out the current exchange rate for a path, you can send a Prepare packet with an unfulfillable (random) condition to the receiver for a certain source amount. The receiver will reject the packet (because it’s impossible to produce the fulfillment for it) and can include how much arrived in the Reject packet.

@emschwartz There’s no RFC nor standard behavior for this type of pricing-information exchange, correct? I don’t think Connector’s will natively do this today, so do you think this deserves its own protocol? Perhaps a new ILPv4 Quoting Protocol, or perhaps something that happens in “health check” messages in the echo/ping protocol?

(See my other post, but I’m thinking that echo/ping should be limited “healthchecking”, and maybe some other protocol should cover metrics, like cost).

@emschwartz

You pick a connector because you think that it generally provides a good balance of cost, latency, throughput, liquidity, and reliability – and because you think it has peered with other connectors of similarly high quality. If it’s bad or seems to have consistently high prices (which could be judged by 3rd party rating services), you’ll switch.

I agree with this statement in the general sense (especially for non-Connectors), but Connector’s themselves will likely have more than one “reliable and well-priced” partner Connector, just as a good business practice.

So, any thoughts around what should be the primary mechanism a Connector should utilize when it has multiple equivalent paths to a particular destination?

For example, consider this topology of Tier-1 Connectors where A wants to send XRP to D, and has two different choices where all of A’s considerations (i.e., latency, throughput, reliability,liquidity) with its two peers are equal, but the price between B/D and C/D is different:

  ┌───BTC┐           ┌─XRP──┐  
  │      │   ┌───┐   │      │  
  │      └──▷│ B │───┘      ▽  
┌───┐        └───┘        ┌───┐
│ A │                     │ D │
└───┘        ┌───┐        └───┘
  │      ┌──▷│ C │───┐      △  
  │      │   └───┘   │      │  
  └────ETH           └─XRP──┘  

Were I running Connector A, I would of course want to this payment to take the lowest-cost path (i.e., "get the most XRP to D).

Aside from simple, “keep testing the paths to check the price”, are there any algorithmic mechanisms that might help here?