Glossary Term

Four Corner Model

The Four Corner Model is the federated network architecture used by Peppol, where invoices travel from sender through two intermediary Access Points to the receiver.

Quick Facts

Corners
Sender → Sender AP → Receiver AP → Receiver
Used by
Peppol
Protocol
AS4
Architecture
Federated

Definition

What is the Four Corner Model?

The Four Corner Model is the network architecture that Peppol uses to exchange electronic documents. It defines four participants ("corners") in every transaction and ensures that no single entity controls the entire network.

The Four Corners

Corner Role Example
-----------------------
Corner 1 Sender Your business (the seller)
Corner 2 Sender's Access Point Your Peppol service provider
Corner 3 Receiver's Access Point Buyer's Peppol service provider
Corner 4 Receiver The buyer's business

Message Flow

Seller → Seller's AP → Receiver's AP → Buyer
  C1         C2              C3           C4

The sender never communicates directly with the receiver's system. All communication goes through the two Access Points, which handle:

  • Format validation

  • AS4 secure transport

  • Delivery confirmation

  • Error handling and retry

    • Why Federated?

    The Four Corner Model is deliberately decentralized:

  • No single point of failure — if one Access Point goes down, the rest of the network continues

  • Competition — businesses choose their own Access Point based on price, features, and service

  • Cross-border — a Dutch Access Point can seamlessly deliver to a Belgian Access Point

  • Privacy — no central authority sees all invoices

    • Compared to Other Models

    Model Architecture Example
    -----------------------------
    Four Corner Federated (2 intermediaries) Peppol
    Three Corner Centralized hub (1 intermediary) Italy SDI, France Chorus Pro
    Two Corner Direct exchange Email, AS2 point-to-point

    Three Corner (SDI)

    In Italy's SDI model, all invoices pass through a single government hub. The government sees every invoice. Simpler architecture, but creates a central dependency.

    Four Corner (Peppol)

    In Peppol, the two Access Points handle routing. No central entity sees all traffic. More resilient, but requires a directory system (SMP/SML) to locate recipients.

    Key Infrastructure

    The Four Corner Model relies on:

  • SML (Service Metadata Locator): Finds which SMP a recipient is registered in

  • SMP (Service Metadata Publisher): Provides the recipient's Access Point address

  • AS4: The secure transport protocol between Access Points