This repository documents the various digital payment processing rails used in the United States. It includes technical overviews, workflows, architecture diagrams, and regulatory compliance considerations for ACH, Wire, RTP, and card-based transactions.
The United States utilizes multiple electronic payment networks for transferring funds between financial institutions. These include:
- ACH (Automated Clearing House) – Batch-processed, low-cost, non-urgent payments (e.g., payroll, bill pay)
- Wire Transfers – Immediate, high-value fund transfers (e.g., real estate, institutional payments)
- RTP (Real-Time Payments) – Instant, irrevocable payments via The Clearing House (TCH)
- FedNow – Federal Reserve's real-time settlement system (launched 2023)
- Card Networks – Credit/debit card clearing and settlement (e.g., Visa, Mastercard)
The Real-Time Payments (RTP) rail is the most modern U.S. rail, operating 24/7/365. Key characteristics include:
- Originating Bank (Sender)
- Receiving Bank (Receiver)
- TCH RTP Network
- ISO 20022 Messaging Layer
- Pre-funded Settlement Accounts
- Directory and Authentication Services
- Payment Initiation – Initiated by a customer or business
- Validation & Authorization – Identity, KYC/AML, and balance verification
- Message Formatting – ISO 20022 messages (e.g.,
pain.001,pacs.008) - Clearing & Routing – TCH RTP routes messages in real-time
- Settlement – Funds are settled instantly using prefunded positions
- Notification – Both sender and receiver are notified in real-time
| ISO Code | Name | Purpose |
|---|---|---|
pain.001 |
Credit Transfer Initiation | Payment instruction |
pacs.002 |
Payment Status Report | Acknowledgment and rejection |
pacs.008 |
Financial Credit Transfer | Actual settlement transaction |
camt.056 |
Reversal Request | Request to reverse a transaction |
camt.052 |
Account Notification | Statement and balance report |
- TCH RTP Rulebook
- NACHA Operating Rules
- ISO 20022 Global Standard
- Federal Reserve Payment Guidelines
- FFIEC Risk Management for Payment Systems
- Real-time fraud screening
- Velocity and amount-based risk rules
- OFAC sanctions screening
- Customer authentication and tokenization
- Audit trails and end-to-end message traceability
documentation/01_Payment_System_Overview.pdfdocumentation/02_ACH_Payment_Flow.pdfdocumentation/03_Wire_Transfer_Process.pdfdocumentation/04_SWIFT_Network_Guide.pdfdocumentation/05_RTP_System_Architecture.pdf
This repository is a complete reference for fintech architects, payment engineers, and compliance analysts building or maintaining U.S.-based digital payment infrastructure.