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.

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Architectural Divergence: Classic vs. EPS

The structural design varies significantly depending on the generation of the software deployment:

End-to-End Component Transaction Flow

1. An ATM transaction arrives at the network interface layer managed by XPNET.
2. The message is routed to the Device Handler, which strips hardware packaging and requests translation from the HSM.
3. The clean internal message passes to the Authorization Engine.
4. If it is a “Not-On-Us” card, the engine identifies the destination BIN and transfers routing control to the Interchange Interface.
5. The Interchange Interface maps the payload to the external scheme standard (such as Visa) and transmits it to the external network.
6. The outbound network response is unwrapped by the Interchange component and tracked through the core engine to log final response codes.
7. 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