Introducing Group Channel Opens on LN+

Posted 3 months ago by LN+

Group Channel Opens is an exciting new feature on LN+ within the Liquidity Swaps section. It allows a group of node operators to open multiple channels with a single bitcoin transaction resulting in massive savings, and automatically balancing channels from the get go. Let me explain the benefits, the drawbacks and requirements for using such swaps.

The Benefits

Only one bitcoin transaction is used to open 3, 4, or 5 channels. This saves block space and consequently makes the channel opening cheaper. Significantly cheaper in fact. In a triangle, square and pentagon the block space and cost savings are appr. 52%, 58%, and 62% respectively.
All channels are balanced on opening. This means both the outgoing and your incoming channel will have 50% capacity, which is ideal for routing payments, and allows you to both send and receive on both channels.
All channels are only opened if all participants in the swap sign the transaction. It's all or nothing.

Single transaction results in 3 channels opened

The Disadvantages

Only works with LND nodes.
Requires BOS (for now) and terminal (command line interface).
All participants need to keep their terminal window open until all participants joined and the transaction is broadcasted, which is why triangles are the best bet in most cases.

Requirements

LND (Lightning Network Daemon) node.
BOS (Balance of Satoshi) command line tool.
Being comfortable copy pasting terminal (command line interface) commands.

How to Do It?

Read the requirements above.
On LN+ go to Liquidity Swaps.
Filter the Swaps for Platform: LND/BOS Only, and join one you like.
If you can't find any matching swaps, start one and within the form select the checkbox: LND/BOS group funded channel open users only. It's recommended to do a triangle, because it's easier for all 3 participants to be online roughly at the same time.
Enable email notifications with a valid email, and watch your inbox.
Invite your friends and followers to the swap.
Follow the instructions and commands provided by LN+.
Wait for the bitcoin transaction to confirm and enjoy your two new channels.
Profit!

This is how the Terminal window will look like from A's point of view, who initiates the transaction. The first command is generated by LN+ for A, and the rest is automated:

bos create-channel-group --allow <pubkey B> --allow <pubkey C> --size 3 --capacity 100000 --fee-rate 5

group_invite_code: <long random string>

at:   Tue Oct 15 2024 09:08:35 GMT+0800 (<Country> Time)ready: <alias B> <pubkey B>
at:   Tue Oct 15 2024 09:08:50 GMT+0800 (<Country> Time)ready: <alias C> <pubkey C>

ready: <alias B> <pubkey B>, <alias C> <pubkey C>

peered: trueproposed: truesigned: true

publishing: <bitcoin transaction hex>
transaction_id: <bitcoin transaction id>
broadcast_transaction_at_height: 865675

This is how the Terminal window will look like from B's point of view who joined the swap. The first command is generated by LN+ for A and B, and the rest is automated:

bos join-channel-group <group invite code>

connecting_to: <A pubkey>
requesting_group_details_from: <A pubkey>

joining: 3 member group coordinated by <A alias> <A pubkey> channels and paying 5/vbyte chain fee
waiting_for_other_members: true
peering_with: <A alias> <A pubkey>, <C alias> <C pubkey>

refund: <long string>

signed: <long signature string>

transaction_id: <bitcoin transaction id>

For more info, also read this previous post explaining batch channel opens, the technology behind Group Channel Opens.

As always, if you see anything broken or you have an idea for an improvement, please comment or send me an email through the contact form.

4 Comments

donteatzebugs wrote 2 months ago

For the adventurous ones, you can do the same thing using bare lnd(lncli) and PSBTs. I have done this without issues during the tough days a year ago when fees were through the roof.

Follow the guide here: https://docs.lightning.engineering/lightning-network-tools/lnd/psbt
IMPORTANT: Read carefully the whole page. The whole process MUST be done withing 10mins. Otherwise you might end up locking the funds involved in the transaction.

02cb636 wrote 13 days ago

LND/BOS Dual Funded Channel Instruction:
Please specify only your side of the capacity, which is half of total channel capacity.

When opening with bos group open 'Capacity in Satoshis' describes:

1. The total capacity of one channel (like with dual-funded)
2. The capacity of each channel divided by two
3. The total capacity of all channels
4. The total capacity of all channels to open divided by two

I guess it maybe clear when running bos but it seems a little unclear when proposing a swap.

LN+ Admin wrote 13 days ago

Thanks! I will improve the text.

02cb636 wrote 12 days ago

Just want to be clear before I start a swap. I find making sure you have that 100,000 reserved and as many sats specified for the channel is important of you'll mess up the timing, especially when mempools are stacked. I think I'll try on a triangle first. Thank you for looking at it.

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