The Pan-European Public Procurement On-Line (Peppol) network has evolved from a regional public sector standard into the dominant global backbone for cross-border B2B electronic invoicing. Built on the OASIS Universal Business Language (UBL 2.1) and the Peppol Business Interoperability Specifications (BIS Billing 3.0), the architecture replaces fragile PDF and OCR pipelines with cryptographically validated XML data interchanges.
1. The Peppol 4-Corner Interoperability Model
Peppol connects disparate ERP systems through a federated four-corner routing topology:
| Corner | Entity Role | Protocol & Security Layer |
|---|---|---|
| Corner 1 (C1) | Sender / Supplier: The billing company initiating the invoice from its ERP or billing software. | Internal API, EDI, or JSON payload to Access Point. |
| Corner 2 (C2) | Sender Access Point (AP): Validates syntax, converts data into Peppol BIS 3.0 UBL XML, signs payload via S/MIME. | AS4 Profile, SMP/SML dynamic addressing lookup. |
| Corner 3 (C3) | Receiver Access Point (AP): Receives AS4 payload, verifies digital signature, validates against Schematron rules. | eDelivery AS4 server with TLS 1.3 mutual auth. |
| Corner 4 (C4) | Receiver / Buyer: The purchasing organization whose ERP ingests the structured invoice directly into Accounts Payable. | Direct ERP ledger ingestion (SAP, NetSuite, Xero). |
2. Dynamic Routing: Service Metadata Publisher (SMP) & SML
Rather than maintaining static point-to-point connections, Peppol uses DNS-based dynamic discovery:
- Service Metadata Locator (SML): Uses DNS CNAME lookups against Top-Level Domains (e.g. edelivery.tech.ec.europa.eu) to locate the recipient's registered SMP.
- Service Metadata Publisher (SMP): Publishes the recipient's endpoint URLs, supported document types (Invoice, Credit Note, Order), and cryptographic public keys.
💡 Schematron Validation Rule Invariant
All Peppol BIS Billing 3.0 documents must pass automated XSLT Schematron validation before dispatch. A single missing tax category identifier (e.g., UNCL5305 code) or rounding imbalance will trigger an immediate hard rejection at Corner 2.
