Channel Rebalancing 通道再平衡

Channel Capacity Example:

Initial State (just opened, single-funded):

  You <-----------[1 BTC]-----------> Counterparty

  Your balance: 1 BTC (100% outbound)
  Their balance: 0 BTC (0% inbound)

Problem: You can send 1 BTC, but cannot receive any payment!

After sending 0.5 BTC:

  You <----[0.5 BTC]--+--[0.5 BTC]----> Counterparty

  Your balance: 0.5 BTC (50% outbound)
  Their balance: 0.5 BTC (50% inbound)

Balanced! Can send/receive 0.5 BTC in both directions

After continuous receiving:

  You <--[0.9 BTC]--+-----[0.1 BTC]----> Counterparty

  Your balance: 0.9 BTC (90% outbound)
  Their balance: 0.1 BTC (10% inbound)

Problem: Insufficient inbound capacity for large payments!

Circular Payment Principle:

Route through other channels back to yourself, moving liquidity

Your node has multiple channels:

                   [Router B]
                  /          \
                 /            \
    needs out   /              \ has outbound
               /                \
           [You]                [Router C]
               \                /
    has in     \              /  needs inbound
                \            /
                 [Router D]

Circular Payment Path:
  You -> B -> C -> D -> You

Effect:
  - You->B channel: outbound decreases, inbound increases
  - B->C channel: unchanged (just routing)
  - C->D channel: unchanged (just routing)
  - D->You channel: inbound decreases, outbound increases

Cost: Routing fees from each node on the path

Submarine Swap Rebalancing:

Get Inbound Capacity (Loop In):

  On-chain BTC -----------> Swap Service
                                |
                            LN Payment
                                v
  Swap Service -----------> Your Node

  Result:
    - You spend on-chain BTC
    - Get Lightning inbound capacity
    - Pay Swap service fee

Get Outbound Capacity (Loop Out):

  Your Node ----LN Payment----> Swap Service
                                    |
                               On-chain BTC
                                    v
  Swap Service -----------> Your on-chain address

  Result:
    - You spend Lightning balance
    - Get on-chain BTC + outbound capacity restored
    - Pay Swap service fee + on-chain fee

Services: Lightning Loop (LND), Boltz Exchange, etc.

Inbound Capacity Market:

Service Types:

1. LSP (Lightning Service Provider)
   - Opens channels to you
   - They provide funds, you get inbound
   - Examples: Voltage, Breez LSP

2. Liquidity Marketplaces
   - Magma (Amboss)
   - Lightning Pool (LND)
   - Node operators bid to provide inbound

3. Channel Leasing
   - Pay rent for inbound for specific duration
   - Counterparty may close channel after lease ends

Lightning Pool Example:

  Auction Market:

  Buyer (needs inbound)        Seller (provides inbound)
    - Bid amount                 - Ask amount
    - Capacity needed            - Capacity available
    - Lease duration             - Minimum lease

  After Match:
    Seller opens channel to buyer, buyer pays lease fee

LND Rebalancing Tools:

1. bos (Balance of Satoshis)
   bos rebalance --amount 100000 \
     --out <depleted_channel_id> \
     --in <full_channel_id>

2. rebalance-lnd
   rebalance.py -t <target_channel> \
     -s <source_channel> \
     -a 100000

3. Lightning Terminal (Automation)
   - Set target balance ratio
   - Maximum fee budget
   - Auto-execute rebalancing

CLN Rebalancing:

1. c-lightning-rebalance plugin
   lightning-cli rebalance -o <out_scid> \
     -i <in_scid> \
     -a 100000sat

2. circular plugin
   lightning-cli circular <amount> \
     <outgoing_channel> <incoming_channel>

Fee Calculation:
  Cost = Sum(routing fee per hop) + base fees
  Rebalance only when: Expected revenue > Cost

Rebalancing Cost-Benefit Analysis:

Scenario:
  - Channel capacity: 1 BTC
  - Current state: 90% local / 10% remote
  - Target state: 50% / 50%
  - Amount to move: 0.4 BTC

Circular Payment Cost:
  - Average routing fee: 0.1% (1000 ppm)
  - Path length: 3-5 hops
  - Cost: 0.4 BTC x 0.1% x 4 hops = 0.0016 BTC
  - About 1600 sats per 10k sats moved

Submarine Swap Cost:
  - Swap service fee: ~0.5%
  - On-chain fee: ~2000 sats
  - Cost: 0.4 BTC x 0.5% + 2000 = ~22000 sats
  - More expensive but more reliable

When Is It Worth It?

                    Expected routing revenue
  Rebalance value = ------------------------- > Rebalance cost
                    Balance maintenance time

  If balanced channels earn extra 500 sats/day,
  then 1600 sats rebalance cost pays back in ~3 days.