The four-corner model describes the technical implementation of file transmission within the Peppol network. Corner 1 is the invoice sender, while corner 4 is the invoice recipient. Invoice recipients need to be registered with the Service Metadata Publisher (SMP) server. When a Peppol participant is registered, the SMP server contacts the Service Metadata Locator (SML) server. There is only one such server in the entire Peppol network: it is centrally operated by the Peppol organisation. Based on specific data, a DNS entry is created for this participant. The address of the DNS entry for the registered participant points to the SMP server where the latter was registered.

To send an invoice via Peppol, Sender 1 (corner 1) needs access to an access point 2 (corner 2). When sending an invoice, the invoice sender sends along the recipient’s participant ID. Based on this ID, access point 2 generates the correct DNS name of the invoice recipient, thus connecting to the appropriate SMP server. In Europe, there are a host of SMP servers which are used or operated by access point 3. All recipients connected to access point 3 are registered with these servers. This registration includes the recipient’s unique participant ID as well as specific settings regarding the documents that can be received via Peppol. At the request of access point 2, the SMP server checks which access point 3 is to be targeted and whether that access point will accept the attached document (compatibility check). Upon approval and feedback of other specific data, access point 2 can now exactly target the recipient’s access point 3, which will then make the invoice available to the recipient.

To ensure standardised document exchange within the Peppol network, communication is implemented on the basis of what is known as BIS (Business Interoperability Specification). The BIS document establishes a clearly defined standard for exchanging documents within the network. For example, if an e-invoice in XRechnung format is to be sent to a recipient via Peppol, a standard business document (SBD) serves as the technical envelope in which the e-invoice (together with the SBD header) is enclosed. It is not necessary to make any changes to the invoice even though the standard of the Peppol network is used. BIS 3.0 is compatible with XRechnung invoices.

4-corner-model

Further information:
A list of compliant SMP implementations is available here: Links to software for Peppol implementations.