{"type":"rich","version":"1.0","author_name":"fiatjaf [ARCHIVE] (npub1v2…pmakl)","author_url":"https://nostr.ae/npub1v2xa40strmvauf2gr5gjj5c3yqlytar7p3v64nfg0ke6e0vkvvkqxpmakl","provider_name":"njump","provider_url":"https://nostr.ae","html":"📅 Original date posted:2019-08-02\n📝 Original message:\nOk, since you seem to imply each question is valuable, here's mine: how\ndoes Alice know RT2 has a route to Bob? If she knows that, can she also\nknow T1 has a route to Bob? In any case, why can't she just build her small\nonion with Alice -\u003e T1 -\u003e Bob? I would expect that to be the most common\ncase, am I right?\n\nOn Friday, August 2, 2019, Bastien TEINTURIER \u003cbastien at acinq.fr\u003e wrote:\n\n\u003e Good morning list,\n\u003e\n\u003e I realized that trampoline routing has only been briefly described to this\n\u003e list (credits to cdecker and pm47 for laying\n\u003e out the foundations). I just published an updated PR [1] and want to take\n\u003e this opportunity to present the high level\n\u003e view here and the parts that need a concept ACK and more feedback.\n\u003e\n\u003e Trampoline routing is conceptually quite simple. Alice wants to send a\n\u003e payment to Bob, but she doesn't know a\n\u003e route to get there because Alice only keeps a small area of the routing\n\u003e table locally (Alice has a crappy phone,\n\u003e damn it Alice sell some satoshis and buy a real phone). However, Alice has\n\u003e a few trampoline nodes in her\n\u003e friends-of-friends and knows some trampoline nodes outside of her local\n\u003e area (but she doesn't know how to reach\n\u003e them). Alice would like to send a payment to a trampoline node she can\n\u003e reach and defer calculation of the rest of\n\u003e the route to that node.\n\u003e\n\u003e The onion routing part is very simple now that we have variable-length\n\u003e onion payloads (thanks again cdecker!).\n\u003e Just like russian dolls, we simply put a small onion inside a big onion.\n\u003e And the HTLC management forwards very\n\u003e naturally.\n\u003e\n\u003e It's always simpler with an example. Let's imagine that Alice can reach\n\u003e three trampoline nodes: T1, T2 and T3.\n\u003e She also knows the details of many remote trampoline nodes that she cannot\n\u003e reach: RT1, RT2, RT3 and RT4.\n\u003e Alice selects T1 and RT2 to use as trampoline hops. She builds a small\n\u003e onion that describes the following route:\n\u003e\n\u003e *Alice -\u003e T1 -\u003e RT2 -\u003e Bob*\n\u003e\n\u003e She finds a route to T1 and builds a normal onion to send a payment to T1:\n\u003e\n\u003e *Alice -\u003e N1 -\u003e N2 -\u003e T1*\n\u003e\n\u003e In the payload for T1, Alice puts the small trampoline onion.\n\u003e When T1 receives the payment, he is able to peel one layer of the\n\u003e trampoline onion and discover that he must\n\u003e forward the payment to RT2. T1 finds a route to RT2 and builds a normal\n\u003e onion to send a payment to RT2:\n\u003e\n\u003e *T1 -\u003e N3 -\u003e RT2*\n\u003e\n\u003e In the payload for RT2, T1 puts the peeled small trampoline onion.\n\u003e When RT2 receives the payment, he is able to peel one layer of the\n\u003e trampoline onion and discover that he must\n\u003e forward the payment to Bob. RT2 finds a route to Bob and builds a normal\n\u003e onion to send a payment:\n\u003e\n\u003e *RT2 -\u003e N4 -\u003e N5 -\u003e Bob*\n\u003e\n\u003e In the payload for Bob, RT2 puts the peeled small trampoline onion.\n\u003e When Bob receives the payment, he is able to peel the last layer of the\n\u003e trampoline onion and discover that he is\n\u003e the final recipient, and fulfills the payment.\n\u003e\n\u003e Alice has successfully sent a payment to Bob deferring route calculation\n\u003e to some chosen trampoline nodes.\n\u003e That part was simple and (hopefully) not controversial, but it left out\n\u003e some important details:\n\u003e\n\u003e    1. How do trampoline nodes specify their fees and cltv requirements?\n\u003e    2. How does Alice sync the fees and cltv requirements for her remote\n\u003e    trampoline nodes?\n\u003e\n\u003e To answer 1., trampoline nodes needs to estimate a fee and cltv that\n\u003e allows them to route to (almost) any other\n\u003e trampoline node. This is likely going to increase the fees paid by\n\u003e end-users, but they can't eat their cake and\n\u003e have it too: by not syncing the whole network, users are trading fees for\n\u003e ease of use and payment reliability.\n\u003e\n\u003e To answer 2., we can re-use the existing gossip infrastructure to exchange\n\u003e a new *node_update *message that\n\u003e contains the trampoline fees and cltv. However Alice doesn't want to\n\u003e receive every network update because she\n\u003e doesn't have the bandwidth to support it (damn it again Alice, upgrade\n\u003e your mobile plan). My suggestion is to\n\u003e create a filter system (similiar to BIP37) where Alice sends gossip\n\u003e filters to her peers, and peers only forward to\n\u003e Alice updates that match these filters. This doesn't have the issues BIP37\n\u003e has for Bitcoin because it has a cost\n\u003e for Alice: she has to open a channel (and thus lock funds) to get a\n\u003e connection to a peer. Peers can refuse to serve\n\u003e filters if they are too expensive to compute, but the filters I propose in\n\u003e the PR are very cheap (a simple xor or a\n\u003e node distance comparison).\n\u003e\n\u003e If you're interested in the technical details, head over to [1].\n\u003e I would really like to get feedback from this list on the concept itself,\n\u003e and especially on the gossip and fee estimation\n\u003e parts. If you made it that far, I'm sure you have many questions and\n\u003e suggestions ;).\n\u003e\n\u003e Cheers,\n\u003e Bastien\n\u003e\n\u003e [1] https://github.com/lightningnetwork/lightning-rfc/pull/654\n\u003e\n-------------- next part --------------\nAn HTML attachment was scrubbed...\nURL: \u003chttp://lists.linuxfoundation.org/pipermail/lightning-dev/attachments/20190802/305c6328/attachment.html\u003e"}