In this post, we will be focusing especially on EN 319 522, which contains the technical specifications for Electronic Registered Delivery Services (ERDS), thus it is the best source to generally oversee e-delivery.

Structurally, EN 319 522 has four parts; the first two parts of the standard (Framework/Architecture and Semantic Contents) provide a general, theoretical background and description which define the overview and the general model for ERDS and give a detailed description of data managed by ERDS; these are considered essential to ERDS and should be implemented in the way they are described in the standard. The second two parts although are pretty much modular. Part 3 (Formats) for example specify several usable formats for metadata (such as S/MIME or AS4) and Part 4 (Bindings) leaves the creation of the actual P-Modes to the implementation.

To best understand the basics of ERDS, it is the first (Framework) part we need to get familiar with.

The standard-part provides us definitions for the more technical expressions and shortened terms. It defines ERDS as „electronic service that transmits data between a sender and recipients by electronic means, provides evidence relating to the handling of the transmitted data, including proof of sending and receiving the data, and that protects transmitted data against the risk of loss, theft, damage or any unauthorized alterations”. In summary, it is used for evidence handling, like what postal service does in the physical world with return receipts, registered mail and such, so it proves that a certain event related to the sent data happened at a certain time. As we now know the main idea of what is ERDS used for, we may continue with how it actually works in practice.

The concept itself can be described with a general model, but it can be modelled in three steps for convenience, where the first step is a so-called black-box model, the second is the 4-corner model and the third is an extended model (Figure 1) which is best used to the general description. The steps mainly vary in the number of ERDSs; the black-box model includes one, the 4-corner model includes two, and the extended model includes multiple ERDSs.

The black-box model is the simplest form of an ERDS, which conveys messages and produces ERDS evidence. User content with metadata can be submitted/received as well as ERDS evidence related to the delivery process. The sender identifies themselves uniquely, then the ERDS associates it to the correct delivery endpoint.

The 4-corner model is a bit more complex, because here the sender and the receiver are subscribed to different ERDSs, thus it can mean that the sender’s ERDS sometimes is not capable of directly delivering the user content to the recipient, but in that case it has the option to relay to a different ERDS with this capability.

Figure 1: the extended electronic registered delivery service model.

Source: ETSI EN 319 522-1; https://www.etsi.org/deliver/etsi_en/319500_319599/31952201/01.00.00_20/en_31952201v010000a.pdf

The extended model is based on the 4-corner one, but instead of using only one ERDS message relay, here the delivery process can go through several chained ERDSs. As the standard states, here the sender's ERDS informs the sender about the outcome of the delivery process based on the trusted information it gets from the last ERDS in the chain. Intermediate nodes implement data/ERDS evidence trusted relay, also additional functionalities like protocol gateway, data/ERDS evidence validation and data/ERDS evidence repository.

So far, we could notice that the main basis of ERDS is events and the related proof, so it is not surprising that the standard dedicates a chapter to present and categorize those. The main categories are Events related to the submission, Events related to the relay between ERDSs, Events related to the acceptance/rejection by recipient, Events related to the consignment to Recipient, Events related to the handover to the recipient and Events related to connections with non ERD systems.

If one wants to get more familiar with e-delivery, it is recommended to read the upper mentioned standards, which are available for download at https://www.etsi.org/standards-search.

Sources:
ETSI EN 319 522-1, Electronic Signatures and Infrastructures (ESI); Electronic Registered Delivery Services; Part 1: Framework and Architecture. https://www.etsi.org/deliver/etsi_en/319500_319599/31952201/01.00.00_20/en_31952201v010000a.pdf