JIT Channels 即時通道

Traditional Channel Opening Flow:

1. User decides to use Lightning Network
2. User buys/transfers on-chain BTC
3. Wait for on-chain confirmation
4. Open channel (another on-chain TX)
5. Wait for channel confirmation
6. Finally can use!

Total time: Hours to days
Entry barrier: Need BTC and technical knowledge first

JIT Channel Flow:

1. User downloads wallet, gets receiving address
2. Someone sends payment to user
3. LSP intercepts payment, instantly opens channel
4. Payment completes through new channel
5. User receives funds, channel established!

Total time: Seconds
Entry barrier: None

Timing Comparison:

Traditional:
[Buy BTC]->[Wait confirm]->[Open channel]->[Wait confirm]->[Use]
   |________________ 1-24 hours ________________|

JIT:
[Receive payment request]->[Open channel + forward]->[Use]
   |________________ seconds ________________|

JIT Channel Opening Flow:

Sender -> Routing Network -> LSP -> New User

Step 1: Payment Arrives at LSP

  Sender initiates payment to user's invoice

  LSP receives HTLC:
    - payment_hash: abc123...
    - amount: 100,000 sats
    - target: user node

  LSP discovers: User has no channel!

Step 2: LSP Instantly Opens Channel

  LSP calculates fee:
    - Channel open fee: 2,000 sats
    - User receivable: 98,000 sats

  LSP opens Zero-Conf channel:
    - Capacity: 100,000 sats
    - User side: 98,000 sats
    - LSP side: 2,000 sats (fee)

  Uses SCID Alias for immediate usability

Step 3: Forward Payment

  LSP forwards HTLC through new channel:

  Inbound HTLC: 100,000 sats
      |
      v
  Outbound HTLC: 98,000 sats (minus fee)
      |
      v
  User reveals preimage
      |
      v
  Payment complete!

Result:
  - User receives 98,000 sats
  - User now has a usable channel
  - LSP collects 2,000 sats fee
  - Entire process transparent to sender

LSPS2: JIT Channels 規範

流程：

1. 客戶端請求 JIT 通道信息
{
  "method": "lsps2.get_info",
  "params": {}
}

響應：
{
  "opening_fee_params_menu": [
    {
      "min_fee_msat": 2000000,
      "proportional": 1000,  // 0.1%
      "valid_until": "2024-01-01T00:00:00Z",
      "min_lifetime": 1008,  // 區塊
      "max_client_to_self_delay": 2016,
      "promise": "signature..."
    }
  ],
  "min_payment_size_msat": 1000000,
  "max_payment_size_msat": 100000000000
}

2. 客戶端購買 JIT 通道
{
  "method": "lsps2.buy",
  "params": {
    "opening_fee_params": { ... },
    "payment_size_msat": 100000000
  }
}

響應：
{
  "jit_channel_scid": "1234567x123x1",
  "lsp_cltv_expiry_delta": 144,
  "client_trusts_lsp": false
}

3. 客戶端創建發票
使用 jit_channel_scid 作為路由提示
發送方支付時，LSP 攔截並開通道

JIT Channel Fee Structure:

Fee Components:
  1. Fixed fee: covers on-chain TX cost
  2. Proportional fee: covers liquidity cost

Calculation Example:
  Minimum fee: 2,000 sats
  Proportional fee: 0.1% (1000 ppm)

  Payment 100,000 sats:
  Fee = max(2000, 100000 * 0.001) = 2,000 sats

  Payment 1,000,000 sats:
  Fee = max(2000, 1000000 * 0.001) = 2,000 sats

  Payment 5,000,000 sats:
  Fee = max(2000, 5000000 * 0.001) = 5,000 sats

Fee Transparency to User:

  Sender pays:    100,000 sats
  JIT fee:         -2,000 sats
  --------------------
  User receives:   98,000 sats

  User knows how much they'll receive before payment

Dynamic Fees (based on on-chain fee rate):
  - Low fee period: lower JIT fees
  - High fee period: higher JIT fees
  - LSP can adjust quotes in real-time

JIT + Splicing Future:

Current (JIT Channels):
  Each new user needs new channel -> new on-chain TX

Problem:
  - If 1000 new users
  - Need 1000 on-chain TXs
  - On-chain fees accumulate

Splicing Solution:

  LSP has one large channel pool

  New user joins -> Splice-in to existing channel
  User leaves -> Splice-out from channel

  Can batch multiple users' splice operations
  Reduces total on-chain TX count

Phoenix Wallet Already Uses This Model:
  - Single channel model
  - All operations via splice
  - More efficient fund management
  - Better user experience