Multipath Payments: Enhancing Lightning Network Capabilities
What Are Multipath Payments?
Multipath payments are an advanced feature of the Lightning Network that allows a single payment to be split across multiple payment channels and routes, then recombined at the destination. This technique significantly enhances the capabilities and flexibility of the Lightning Network.
Instead of being limited by the capacity of a single channel, users can leverage multiple channels simultaneously to send larger amounts or find more efficient routes.
How It Works
A single payment is divided into multiple smaller payments, each taking a different path through the network. These partial payments are then merged at the destination, where the recipient receives the full amount.
Each partial payment still uses the same cryptographic security principles as regular Lightning payments, ensuring the same level of security.
Key Benefits
- Overcome single channel capacity limitations
- Improve payment success rates by utilizing multiple routes
- Enhance privacy by splitting amounts across multiple paths
- Optimize fee costs by utilizing cheaper routes in parallel
- Increase payment reliability through redundancy
Types of Multipath Payments
Basic Multipath Payments (MPP)
The original implementation of multipath payments, where a single payment is split into smaller parts that all use the same payment hash but travel through different routes.
- All parts share the same payment hash
- Receiver must collect all parts to claim the payment
- Implemented in most Lightning implementations
Atomic Multipath Payments (AMP)
An advanced version that uses multiple payment secrets (preimages) that are combined to form a single payment hash, providing enhanced security and atomicity guarantees.
- Uses multiple preimages and a shared payment hash
- All parts succeed or fail together (atomic)
- Provides stronger security guarantees
Technical Implementation Differences
| Feature | Basic MPP | Atomic MPP (AMP) |
|---|---|---|
| Payment Hash | Single shared hash | Multiple hashes combined cryptographically |
| Atomicity | Basic, recipient enforced | Cryptographically enforced |
| Privacy | Good | Enhanced |
| Implementation Complexity | Lower | Higher |
Multipath Payment Routing Strategy
Effective multipath payments require sophisticated routing algorithms to determine how to split a payment across multiple channels and routes:
Path Selection
The sender's node evaluates all available channel routes to the destination, considering factors like capacity, fees, reliability, and previous success rates.
Payment Splitting
The payment is divided into multiple parts based on available channel capacities, network conditions, and optimal splitting ratios to minimize overall fees.
- Route A: 200,000 sats (fee: 20 sats)
- Route B: 150,000 sats (fee: 15 sats)
- Route C: 150,000 sats (fee: 18 sats)
Parallel Execution
All partial payments are initiated simultaneously, each following its own route through the network toward the destination.
Destination Aggregation
The receiver's Lightning node collects all the partial payments and processes them as a single logical payment, generating just one invoice for the sender.
Implementation Challenges & Solutions
Technical Challenges
- Path DiversityFinding sufficiently diverse paths to allow effective splitting
- Routing ComplexityIncreased computational cost of finding multiple routes
- Payment CoordinationEnsuring all parts arrive at roughly the same time
Solutions & Best Practices
- Path ScoringImplementing sophisticated scoring algorithms for path selection
- Parallel ProcessingOptimizing code for simultaneous payment part handling
- Failure HandlingSophisticated retry mechanisms for partial payment failures