Improving Routing in the Lightning Network with Trampoline Payments

Scaling Bitcoin 2019

Bastien Teinturier (ACINQ)@acinq_co @realtbast

The Lightning Network, a Payment Channels Network

Alice Bob

You can pay anyone you can find a route to!

Payment Routing: Fees and Lock Time

Intermediate channels advertise a fee rate:

● base fee● proportional fee

And a lock time delta:

● to protect their funds● and avoid locking capacity for

too long

Gossiped via staggered broadcast.

AliceBob

fb = 0.1 BTCf% = 1%Δ = 14

Carol

? BTC ? BTC ? BTC ? BTC

8 BTC5 BTC

2 BTCExpiry: 1105

2.12 BTCExpiry: 1119

Payment Routing Features

Powerful features

● Optimal path (source routing)● Trustless (HTLCs)● Private (onion encryption)

But at a cost…

● Bandwidth● Memory● CPU● Which impacts mobile UX

sender recipient

Does not know its position in the route .i.e

● Does not know who the sender is● Does not know who the final recipient is

1000 satExpiry: 9

1005 satExpiry: 18

1008 satExpiry: 25

Lightning Payment Triangle of Success ©

Privacy

Route cost optimum Performance

we’re here!

We really don’t want to be there...

this side looks interesting too...

Let a billion payment channels bloom...

A phone isn’t a server (duh):

● not always online● unreliable connections● limited performance● handy payment method

What if?

● sync smaller graph● and special nodes● trade fees for performance

Trampoline Routing

Partial source routing:

● select trampoline nodes● route to first one

Routing between trampoline nodes is deferred to the trampoline nodes themselves.

Powered by variable-length onions (onion nesting FTW).

1

2

Gossip Filters

Reduce bandwidth usage:

● channel_update filters○ n-radius○ channel capacity

● node_update filters○ fee rate○ lock time○ probabilistic (distance to block hash?)

Applied before forwarding gossip.

Without BIP 37 drawbacks!

init

channel_update_filter

node_update_filter

…...

channel_update_filter

Alice Bob

Fee Estimation

Trampoline nodes broadcast aggregated trampoline fees and lock time (node_update).

Mobile nodes may build a reputation score DB to prune unreliable trampoline nodes.

Custom heuristics may be added depending on node connectivity and performance.

f = 5, % = 0.5, Δ = 12

f = 2,

% =

0.1,

Δ =

9

f = 3, % = 0.2, Δ = 6

f = 10, % = 0.01, Δ = 3

f = 0, % = 0.1, Δ = 3

f = 2,

% =

0.05,

Δ = 5

f = 12, % = 0.5, Δ = 15

AMP 💙 Trampoline

0.5 BTC0.4 BTC

0.1 BTC0.1 BTC

0.25 BTC

0.1 BTC

0.1

BTC

0.1 BTC

0.15 BTC 0.15 BTC

#reckless

To Infinity and BeyondIncremental change to payment infrastructure.

Easy to rollout.

Coming to eclair soon.

Incremental step towards hierarchical systems.

Feedback wanted!https://github.com/lightningnetwork/lightning-rfc/pull/654https://lists.linuxfoundation.org/pipermail/lightning-dev/2019-August/002100.html

Questions?