Model 16 · Network
The Lightning Channel Machine
Many payments, two blockchain transactions when closed cooperatively.
Explanation level
How to use this model
How to use this modelWhat you see, what you can touch, what changes, what to take away
What am I looking at?
A precision bench: Alice's and Bob's stations on either side of a shared channel trough whose piston divides the capacity, a two-key lock beneath it and a chain rail for the funding and closing transactions.
What can I touch?
- Open a simulated channel
- Choose channel capacity
- Send payments from Alice to Bob
- Send payments from Bob to Alice
What happens when I change something?
Send a payment and the piston moves: the sender's share shrinks and the receiver's grows by exactly that amount, the capacity stays the same, and nothing new appears on the chain rail until the channel is closed.
What should I understand afterwards?
Explain why payments inside a channel do not each need a blockchain transaction.
Understand payment channels as shared spending arrangements updated without recording every payment on the blockchain.
A shared box with two keys.
After this you can
- Explain why payments inside a channel do not each need a blockchain transaction.
Move balances and experiment with payment capacity.
Open, pay both ways, hit the limits, close.
After this you can
- Predict whether a payment will succeed from the sender's outbound liquidity.
Examine funding outputs, commitment transactions, channel states, liquidity and settlement.
2-of-2 funding output, commitment numbers, reserve, cooperative close.
After this you can
- Distinguish channel capacity, outbound liquidity and the channel reserve.
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Missions operate the model to complete them
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Capacity is not liquidity
BeginnerCompletedFind out the hard way that a channel's size is not what each side can send.
Your task: Open a 500,000 sat channel. Try a payment that fails for lack of outbound liquidity, then make payments that succeed so that both sides hold some of the channel.
Use: Open a simulated channel · Choose channel capacity · Send payments from Alice to Bob · Send payments from Bob to Alice · Explore insufficient outbound liquidity
A channel's capacity is fixed when it opens. What each side can send is its own balance (minus the reserve); payments move that balance across, they do not change the capacity.
Missions are checked from the model's own simulation state, not from clicks. No time limit. Completion is stored only in this browser. The quiz questions in the learning paths remain available.
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Common mix-ups
- Myth: A 1,000,000 sat channel lets either side send 1,000,000 sat.
- In fact: Each side can only send its own balance above the reserve; the capacity is shared.
- Myth: Every Lightning payment is a small on-chain transaction.
- In fact: Payments update the channel's commitment state; only opening and closing are on-chain.
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