The BASE24 electronic payment system developed by ACI Worldwide exists in two primary architectural generations:
BASE24 Classic (historically deployed on HPE NonStop / Tandem fault-tolerant hardware) and
BASE24-eps (Enterprise Payments System, built using an object-oriented C++ framework deployable across open systems, z/OS, and cloud infrastructure).
Despite structural differences, both share a highly optimized, component-based transaction routing engine.
Core Structural Component Layers
The component architecture maps the complete end-to-end lifecycle of a financial message (such as ISO 8583) through five distinct functional sub-systems:
1. Network & Message Routing Component (XPNET)
- Purpose: Coordinates all message traffic across internal processes and physical network nodes.
- Function: Operates as a specialized middleware network manager that decouples low-level communication links from upper transaction routing layers.
- Configuration: Relies on a Logical Network Configuration File (LCONF) to define active execution nodes, hardware lines, and physical stations.
2. Perimeter Access Layer (Device Handlers)
- Purpose: Translates device-specific message protocol formats into the system’s unified internal format.
- ATM Device Handlers (ATMDH): Manage direct connectivity to automated teller machines, unpack specific vendor dialects (such as Diebold or NCR states), and track terminal hardware statuses.
- POS Device Handlers (POSDH): Interface with point-of-sale acquirer terminals and merchants.
- Security Operations: Triggers immediate payload encryption/decryption and Hardware Security Module (HSM) PIN-block translation directly within this ingestion ring.
3. Core Transaction Logic (Authorization System)
- Purpose: Determines whether a payment request should be accepted, rejected, or modified.
- Full On-Us Authorization: Inspects internal databases for matching account records, positive balances, and velocity thresholds to issue real-time decisions.
- Parametric/Negative Checks: Validates card status against offline negative files, usage restrictions, or custom risk parameters.
- Scripting Engine: Modern BASE24-eps variants execute localized transaction routing scripts via customized operators without forcing a compile rewrite of the core engine core.
4. Boundary Channels (Interchange & Host Interfaces)
- Interchange Interfaces (ICH): Package and transform the transaction payload into international network profiles (e.g., Visa, Mastercard, regional switches). It handles strict message mapping and regional network check requirements.
- Host Interfaces (HIF): Create synchronous links back to an institution’s underlying Core Banking system to apply ledger adjustments, check balances, or execute real-time holds.
5. Offline & Administrative Subsystems
- Extract Component: Gathers active transaction logs and streams filtered payloads out to analytical reporting databases.
- Refresh Component: Updates terminal operational data, key packages, and card exclusion lists from parent systems down to active execution nodes.
- Settlement Initiator: Groups, cleanses, and batches net-clearing totals to finalize payment entries into regional clearinghouses.
Architectural Divergence: Classic vs. EPS
The structural design varies significantly depending on the generation of the software deployment:
End-to-End Component Transaction Flow
- An ATM transaction arrives at the network interface layer managed by XPNET.
- The message is routed to the Device Handler, which strips hardware packaging and requests translation from the HSM.
- The clean internal message passes to the Authorization Engine.
- If it is a “Not-On-Us” card, the engine identifies the destination BIN and transfers routing control to the Interchange Interface.
- The Interchange Interface maps the payload to the external scheme standard (such as Visa) and transmits it to the external network.
- The outbound network response is unwrapped by the Interchange component and tracked through the core engine to log final response codes.
- The transaction safely records inside the active log file, allowing the Extract / Settlement components to pick it up later during batch processing.
BASE24 and BASE24-eps architecture overview
