# WIA-FIN-012 Phase 3: Processing Protocol Specification

**Version:** 1.0.0  
**Status:** Final  
**Date:** 2025-01-15  
**Category:** Finance - Payment Systems

## Overview

This specification defines the card network routing protocols, clearing and settlement processes, dispute resolution, and risk management systems.

## Card Network Routing

### Visa Network Flow

```
Terminal → Acquirer → VisaNet → Issuer
   ↓          ↓          ↓         ↓
  PAN     Format     Route    Authorize
  Swipe   ISO 8583   BIN      Approve/Decline
           0100      Table     0110 Response
```

### Message Flow Timing

- Terminal to Acquirer: < 100ms
- Acquirer to Network: < 200ms
- Network to Issuer: < 150ms
- Issuer Processing: 200-500ms
- Total Round Trip: < 2-3 seconds

## ISO 8583 Protocol

### Message Types

- 0100: Authorization Request
- 0110: Authorization Response
- 0200: Financial Transaction
- 0400: Reversal Request
- 0800: Network Management

### Response Codes

- 00: Approved
- 05: Do Not Honor
- 51: Insufficient Funds
- 54: Expired Card
- 57: Transaction Not Permitted

## Settlement Process

### Clearing Cycle

1. **T+0**: Transaction authorized
2. **T+0 EOD**: Batch submission
3. **T+1**: Clearing process
4. **T+2**: Fund settlement
5. **T+3**: Merchant funding

### Interchange Fees

| Card Type | Rate |
|-----------|------|
| Visa Credit | 1.51% + $0.10 |
| Visa Debit | 0.80% + $0.10 |
| MC Credit | 1.58% + $0.10 |
| MC Debit | 0.85% + $0.10 |
| Amex | 2.50% + $0.10 |

## Chargeback Process

1. Cardholder disputes charge
2. Issuer initiates chargeback
3. Acquirer debits merchant
4. Merchant has 10 days to respond
5. Representment or acceptance
6. Arbitration if unresolved

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