Four-corner model

The four-corner model connects two businesses via their respective access points.

Definition

The four-corner model describes the exchange topology used by PEPPOL. The four corners are:

1. The sender (corner 1), which produces the document.
2. Its sender access point (corner 2), which sends it onto the network.
3. The receiver access point (corner 3), which receives it.
4. The receiver (corner 4), which processes it.

Each business connects only to its own provider; it is the two access points that talk to each other under shared rules.

Why this model

The key advantage is the 'connect once, reach everyone' principle. Instead of establishing a direct connection (two-corner model) with each partner, each actor:

• Picks a single compliant access point.
• Inherits the ability to exchange with every other participant on the network.
• Relies on shared format and transport standards, guaranteed by the access points.

This sharply reduces the number of connections to maintain and eases interoperability at scale.

Good to know

Some national CTC models add a fifth corner: the tax authority platform, which receives a copy or a report of the transaction. This is called a five-corner model. The four-corner model remains the baseline, extended to meet local reporting obligations.