The 4-corner model describes the technical implementation of file transfers within the Peppol network. Corner 1 represents the invoice sender and corner 4 the invoice recipient. Invoice recipients must be registered in the SMP (Server Metadata Publisher) server. When Peppol participants register, they contact the SML (Service Metadata Locator here) server. There is only one of these servers in the entire Peppol network and it is operated centrally by the Peppol organisation. This server then creates a DNS entry for that participant from certain data. The DNS entry for the registered participant appears on the SMP server with which the participant registered.

To send an invoice via Peppol, sender 1 (corner 1) must have access to an Access Point 2 (corner 2). When sending the invoice, the invoice sender now provides the recipient’s participant ID. Using this ID, Access Point 2 generates the correct DNS names for the invoice recipients and thus reaches the associated SMP server. There are a number of SMP servers in Europe that can be used or operated by Access Points 3. All recipients connected to Access Point 3 are registered there. This includes the recipient’s unique Participant ID and specific settings for the documents to be received via Peppol. Thus, upon a request from Access Point 2, the SMP server checks which Access Point 3 is to be accessed and whether or not said Access Point accepts the document supplied (compatibility check). Once approved and upon confirmation of other specific data, Access Point 2 can now access the recipient’s specific Access Point 3. This makes the invoice available to the recipient.

To ensure that exchanges in the Peppol network proceed in a standardised manner, communication is implemented using the so-called BIS (Business Interoperability Specification). This defines a clear standard for the exchange of documents within the network. For example, if an XRechnung invoice is to be sent to a recipient via Peppol, a Standard Business Document (SBD) forms the technical envelope in which the XRechnung invoice is embedded. Nothing on the invoice needs changing but the PEPPOL network standard will still be used. This is possible with an XRechnung invoice with BIS 3.0.

Further information:
A list of compliant SMP implementations can be found on the Links to Software for PEPPOL Implementations page.