Foxboro A4H124-24FX P0973JN – High-Reliability Fiber Switch for Process Control Networks

Brand ABB

Model Foxboro A4H124-24FX P0973JN

Product Overview

The Foxboro A4H124-24FX P0973JN is a high-density managed fiber Ethernet switch specifically engineered for the field control networks of Foxboro I/A Series and Evo Distributed Control Systems (DCS). Manufactured by Enterasys Networks (now part of Extreme Networks) and OEM-branded by Foxboro, the Foxboro A4H124-24FX P0973JN serves as a critical aggregation point for terminating multimode fiber links originating from field-mounted FBM (Field Bus Module) controllers and routing that traffic to the central control backbone via Gigabit uplinks. Its primary role is to establish a highly reliable, electromagnetic-interference-immune communication path from distributed process cabinets to the control room.

In a Foxboro DCS architecture, the Foxboro A4H124-24FX P0973JN occupies the edge aggregation layer. The 24 fixed 100BASE-FX MT-RJ multimode fiber ports are dedicated to connecting FBM I/O modules dispersed across various process areas, effectively eliminating the electromagnetic interference issues commonly associated with copper cabling near motors, variable frequency drives, and MCC cabinets . Unlike commercial IT switches, the Foxboro A4H124-24FX P0973JN comes factory-configured with QoS priority rules tailored for Foxboro control traffic, ensuring control packets receive the highest forwarding priority to maintain deterministic and real-time process control.

This switch belongs to the Enterasys SecureStack A4 series platform and supports stacking expansion, allowing up to eight identical switches to be consolidated into a single logical management domain, significantly enhancing fiber access port density and unified management efficiency in large-scale plants . Although the Foxboro A4H124-24FX P0973JN is now in a mature lifecycle stage, its spare parts value in maintaining, expanding, and upgrading existing Foxboro DCS installations remains irreplaceable, making it a critical hardware asset for sustaining the stable operation of legacy control networks.

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Description

Technical Specifications

Parameter Name	Parameter Value
Product Model	Foxboro A4H124-24FX P0973JN
Manufacturer	Enterasys Networks / Foxboro (Invensys)
Product Type	Managed Fiber Ethernet Switch
Fiber Ports	24 × 100BASE-FX MT-RJ Multimode
Uplink/Stacking Ports	2 × 10/100/1000BASE-T RJ45
SFP Uplink Slots	2 × Gigabit SFP
Switching Capacity	12.8 Gbps
Forwarding Rate	9.5 Mpps
MAC Address Table	16,000 entries
VLAN Support	4096 IEEE 802.1Q VLANs
Stacking Capability	Up to 8 units
Management Protocols	SNMP v1/v2/v3, RMON, CLI, Web
Power Input	AC 100–240V, 50/60 Hz
Operating Temperature	0°C to +50°C
Dimensions	1U Rackmount, approx. 442 × 44 × 368 mm
Installation	19-inch Standard Rack

Main Features and Advantages

The core design philosophy of the Foxboro A4H124-24FX P0973JN revolves around the unique requirements of industrial process control networks. Its advantages lie not in competing on generic switching performance parameters, but in deep adaptation to the Foxboro DCS ecosystem and an uncompromising commitment to field reliability.

Native Fiber Port Integration Eliminates EMI Risks. The 24 100BASE-FX ports of the Foxboro A4H124-24FX P0973JN utilize MT-RJ multimode fiber interfaces, enabling direct connection to field FBM controllers’ fiber outputs without external media converters. This design physically severs ground loops and conducted electromagnetic noise paths, allowing the switch to operate stably in electrical environments dense with variable frequency drives, high-power motors, and MCC cabinets, significantly reducing link flapping and CRC errors caused by copper cable interference .

Foxboro Pre-Configured QoS Ensures Control Traffic Priority. The Foxboro A4H124-24FX P0973JN comes with built-in QoS rule sets specifically for Foxboro I/A systems. It automatically marks DCS control packets and Modbus TCP traffic into the highest priority queue, while historian data collection and background management traffic are relegated to lower priority. This mechanism requires no manual configuration by field engineers, functioning immediately upon power-up, effectively preventing control command delays or loss under heavy background traffic loads.

Stacking Expansion Capability Adapts to Large Plant Network Topologies. The Foxboro A4H124-24FX P0973JN supports stacking up to eight devices through dedicated stacking ports into a single logical switch with unified IP management . For large factories with multiple control cabinets or dispersed process units, this feature allows smooth, modular expansion of fiber access port count without re-architecting the entire network.

Industrial-Grade Hardware Design for Cabinet Installation Environments. The Foxboro A4H124-24FX P0973JN employs a fanless passive cooling design, eliminating fan failure—a common switch failure mode—making it particularly suitable for unattended process control cabinets . Its standard 1U rack form factor and wide-range AC power input allow direct installation in Foxboro DCS field cabinets, sharing the same electrical environment as FBM modules and field wiring.