Most Important Challenges of Instant Payment

Required knowledge

• Processing instant payments in the SIC IP service
• Basics of the SIC protocol

The key challenges in implementing instant payment are 24/7/365 availability and guaranteed processing time. Both aspects affect the SIC IP service in the SIC system and the participants connected to it in the same way. After all, instant payments can only run smoothly if the system and its participants are constantly available and processing times are met. Large maintenance windows, where IT systems are shut down, maintained, and restarted over an extended period of time, are no longer possible in this mode. We need to make adjustments to the system and turn on new features while it is running. This can hardly be done in a globally coordinated manner. All of these aspects require adjustments in the operational scenarios as well as in the architecture of the IT systems involved in order to enable this type of operation at all.

Technical Availability Through Redundancy

On a technical level, IT systems may require updating components with new software, restarting processes, and rebooting machines. In addition, you can never completely rule out the possibility that components will simply break or otherwise fail. Therefore, continuous technical availability of an IT system can only be achieved if its individual components are designed redundantly, i.e., with multiple availability. If one component needs maintenance or fails, the remaining component can seamlessly take over.

However, a redundant and always available system is useless if the connections to it are not redundant as well. The SIC protocol relies on long-lived, persistent network connections that participants must initiate each time. If one of the end points of such a connection – either in the SIC IP service or on the participant’s side – fails due to maintenance work or an error, it results in a connection being interrupted and the participant can no longer be reached. This scenario is indistinguishable from a system failure.

What does this mean in concrete terms? The SIC IP service is already technically designed for uninterrupted operation due to the necessary redundancies. However, system participants must also design their IT systems in such a way that planned or unplanned failures of subcomponents do not cause any interruptions in processing and that the connection to the IP service is available at all times.

To keep the connection uninterrupted, the SIC IP service provides the participants with two independent connections, ensuring that at least one of the two accesses is always available. Participants are required to connect to at least one communication interface with each of these accesses. If the connection to one of the accesses is interrupted, the other access is still fully available.

Professional Evolution Through Compatibility

In terms of functionality, the SIC IP service will evolve over time with new or adapted functions. For such functional adjustments, the service provides migration mechanisms for a seamless transition.

In principle, any new externally visible adaptation of the SIC IP service will be rolled out in a manner that is compatible with the previous version. Participants are therefore not forced to respond in a coordinated manner to a system adjustment.

A typical example is the transition to new message versions. The SIC IP service will support the current and the new version in parallel for a certain period of time. Furthermore, the SIC IP service is able to convert messages to the version currently used by the participant. This makes it possible to migrate the service and the various participants to new message versions independently of each other. This eliminates the need for a coordinated simultaneous migration of the system, including all participants.

Processing Time in Milliseconds

The processing of an instant payments takes a maximum of ten seconds from order placement to crediting. If this process takes longer, the SIC IP service cancels the processing of the payment. For the benefit of participants, SIC ensures that payment processing time within the SIC IP service is as short as possible. Typically, in-system payment processing will take less than 200 milliseconds per payment. The remaining 9.8 seconds are thus available for processing on the participant’s side and for communication.

Stefan Ferstl
Lead Architect SIC Platform, SIX