Good Morning ZmnSCPxj! I was thinking using the normal onion-routing, probably modified in some way so it can read and modify max. Must admit I haven't studied that part at that level at all.
For simple three-member constructs it could be enough with a simple non-onion message that A asks B if it would like to rebalance AB,BC and A asks C if it would like to balance BC,CA. But first it seems I have to at least try to convince you that rebalancing does help solve some problems. I think rebalancing is good for many reasons. Consider a node A that has the following channel balances. It initiated A-B with 100sat and used that up instantly. C initiated an inbound channel of 200sat. A made a new channel A-D with 300sat It ended up looking like the following: A-B 0-100 A-C 0-200 A-D 300-0 For simplicity in this case the total balance is 300-300. Also lets say "balanced" means "able to send and receive 25 sat". Achieving total balance on all channels is not realistic. It's up to each node to decide their own definition. A has only one channel to send out via. If D goes down it has even fewer. So my idea is: A finds if there exists any D-C channel (or multi-hop), and politely asks whomever it may concern if sending 100 sat A->D->C->A would benefit them as well. if it does you send over 100 sat and will end up with A-B 0-100 A-C 100-100 A-D 200-100 If the agreed max along the path is lower, it will have to do, it helped a little bit, but lets say 100sat was ok with everyone Repeat for A->D->B->A and 50sat and you will have A-B 50-50 A-C 100-100 A-D 150-150 Now A instantly have 3 times as many possible routes out, and 50% more possible routes in, nobody had to go to the chain to close/open/splice, and nobodys channel went unbalanced, and nobody paid anyone. The possibilites for others in the network to actually route via A increases to all 6 paths from 2, before only B->A->D and C->A->D would succeed. So there is also a 3-fold increase. Consider a bigger node with say 40 channels where 10 has too low local balance and 30 has too low remote balance. It would have 300 working paths out of 1560, so about 80% failure rate. So, for redundancy and maximum possible routes, I think rebalancing is good. The main difference with this protocol compared to how we balance lightning channels today is * that everyone benefits from it (or else would deny to be a part of it) so there are not any fees * today channel balances sometimes start oscillating if two nodes try to balance a channel somewhere in the network according to their own will, without caring/knowing about the intermediates wishes or eachothers. now we care. * less trial and error since you know the perfect amount to send --- In the case you describe, it is a feature, not a bug. If you find a path A->B->C->D C would like to balance BC against CD so it offers a rebalance and accepts fee-free transactions for things coming in BC and goes out CD. But maybe DB channel doesn't exist or have too little capacity. It's wishes to rebalance the channel remains. Then suddenly your payment goes thru and achieves the same goal, I don't see a problem. if C did *not* want to balance in that direction, it would have rejected passing the payment for free if two payments pass thru the same channels, the second one will be rejected as normal with "feeinsufficient" If we do want to avoid this (maybe because too many flood the network probing to find a free hop), you can send the future payment hash, or part of it, in the proposal message, and whitelist that hash for 1337 seconds. Even if whitelisted, when/if the payment packet arrives, the node shall check in&out channel and amount to see if it is still beneficial, otherwise just reject it. The agreed max is a soft promise. Regarding receive-only or send-only nodes and on/off swapping, I think those are entirely separate problems. My solution only aims at spreading the existing grease around the layer two for smoother operation. Best Regards Robert Olsson On Mon, Aug 13, 2018 at 1:16 PM, ZmnSCPxj <zmnsc...@protonmail.com> wrote: > Good morning Robert, > > I assume, this functionality is transported also via the same > onion-routing-packet style that current payment routing uses? > > If so, then it seems this feature can be used by a payer and payee to > coordinate to locate some route that would, if paid normally, charge fees, > but if using the "free rebalancing" could be made free. The payer simply > locates some route, adds a synthetic initial balance that is much higher > than the payment to be forwarded, and then request for a "free rebalancing" > from the payer to the payee. If at the payee node, the resulting "max" is > greater than the actual payment being sent, then the payer and payee have > found a fee-free route between them. > > After all, since the functionality is transported by onion-routing-packet, > then intermediate hop routes cannot know that the ultimate source and > ultimate destination are different nodes. > > Note that intermediate nodes cannot detect this at all. A fee-free > rebalance request that follows the fee-free rebalance query may be lower > than the max it forwarded, since, a later intermediate node on the route > might have lowered the maximum already. > > -- > > For myself, I think rebalancing is not a particular good solution to > anything (similar to splice). > > Imagine a simple 3-member cyclic-superhub network composed of A -> B -> C > (looping back to -> A). Node A may pay node C via B, and so on. Now if C > is a popular merchant for both B and A, then both the B-C and C-A channels > will saturate in favor of C. In such a case, no rebalancing is possible. > > A better solution is for C to purchase more incoming balance by asking > either of B or A to transfer onchain funds in exchange for a preimage (i.e. > swap offchain funds for onchain funds). This is effectively "batching" the > earnings that C gains in LN: C might earn a lot of small amounts, each one > too small individually to justify onchain transfers, but which batched > together can justify the onchain transfer. Further, this batching is > noncustodial and C can close the channel at any time (incurring an onchain > fee), unlike current payment processors (PayPal, credit cards) where > payment batching is custodial and may be frozen by the custodian; on LN, at > worst the money will be locked for a few days or weeks, but will definitely > be returned to you as long as you did not actually cheat. > > Further this swapping can be done on a separate layer/software that > interacts with ordinary existing LN software without requiring additional > changes at the LN protocol level, which is always a good thing: I believe > we should prefer to make LN a layer that supports further layers, not put > every possible feature into LN. > > This off-to-on and on-to-off swapping solves the same problems that both > rebalancing and splcing do (channel balancing, incoming channels, channel > reloading) without requiring changes at the LN layer, merely adding an > application on top of LN. > > Regards, > ZmnSCPxj > > > > Sent with ProtonMail <https://protonmail.com> Secure Email. > > ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐ > On August 12, 2018 7:31 AM, Robert Olsson <rob...@robtex.com> wrote: > > Dear All, > > I'd like to suggest a new function in the network, "Free Rebalancing > Proposals" > It is a fee-less, omni-beneficial rebalancing scheme > > Background: > > I currently balance my nodes in the following way, extremely simplified: > > 1) Identify channels that have too low remote_balance (A) and too low > local_balance (B) for being of any use (in that direction) > 2) Find potential routes and amounts between all channels A and all > channels B that would optimize at least one of them > 3) Send a payment along those possible routes for different amounts, > sorted after fee, until one succeeds > > It works quite good and is quite straight forward until the third step. So > I would like to propose a better solution which works like this: > > Send a proposal-for-balancing-message over channel A, and the max amount > you would propose to balance in that direction. > > Each node analyses the in and out channels and adjusts the max to it's own > desire to balance. Max can only be adjusted down. Let's say the function is > `int freeBalancerMax(channel in,channel out)`. It could be as simple as > checking how near "in" is to 100ksat local_balance and "out" is to 100ksat > remote_balance. The node passes that message with new max value on to the > next node, much like a normal payment. > > When this packet comes back to the origin it will know how much the > intermediate nodes are willing to let you balance, or if someone is > reluctant to balance (and the final max value would be 0) > > If everyone is happy (i.e. max>0), the origin node sends a payment along > this node, *without* dropping off any fees along the way, since all nodes > agreed and benefit from the rebalancing act. > > Since all intermediate nodes benefit they are happy to do this without > fees. Since they adjust max values to their desire it will stop multiple > attempts from different nodes from starting to oscillate the balances in > the channels, but will instead reach some kind of equilibrium as long as > the node suggesting proposal uses it's freeBalancerMax when proposing and > accepting proposals. > > The intermediate nodes might not need to keep track of any agreements to > balancing proposals, it can simply call the freeBalancerMax function, and > if the payment is lower, it passes on the payment even if it didn't get any > fees, otherwise it fails as usual. If someone tries to send a non agreed > payment without fees, but it coincides with the nodes own desire to > rebalance, there is no harm done. Only problem with that is that senders > might flood a path with creative attempts trying to find a path with a > fee-free hop. I think things like that will be stopped by a general > throttle functionality which probably will be needed anyhow. > > Best regards > Robert Olsson > > > > > > > > > > > > > > > > > > >
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