Deltron Equipment & Systems Pvt. Ltd.
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Fail-Safe Network Multiplexer
Introduction
The Failsafe Network Multiplexer (FN-Mux) is an advanced, modular system designed to facilitate the safe and reliable exchange of vital digital I/O information across railway signalling applications. Built on a distributed architecture, it consists of networked multiplexer modules that communicate seamlessly to ensure real-time synchronisation of Vital and Non-Vital I/O between control centres and field locations.
This robust system allows for the formation of a scalable, centralised multiplexer hub—known as the FN-Mux Central Unit (CU)—which consolidates Inputs and Outputs from multiple Field Units (FUs) distributed across the network. The intelligent safe ethernet SafetyNetP protocol and addressing scheme adopted allows any vital module—whether within a Central or Field Unit—to virtually connect point-to-point or multipoint, offering complete deployment flexibility.
Importantly, system can also handle Vital and Non-Vital I/O, simultaneously in a single system and also supports data logger connectivity for seamless event recording and diagnostics.
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Fail-Safe Network Multiplexer Unit
FN-Mux Network Architecture with Dual Optic Fiber Ring
Fail-Safe Network Architecture for a typical 16 Node Network with 16 Inputs & 16 Outputs at each Node
A Closer Look at the FN-Mux System
Fail-Safe System Architecture (2 out of 2 CENELEC SIL-4 in Hot-Standby)
Close-Up of Fail-Safe Network Multiplexer Unit - Digital System
System Composition of FN-Mux
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​FN-Mux Central Unit (CU) – Core of the Network
The Central Unit is the main command center for the FN-Mux system, comprising a variable number of vital modules, all housed within a modular and expandable chassis.
The FN-Mux system is built on a robust fail-safe 2oo2x2 architecture, fully compliant with CENELEC SIL-4 standards, and offers hot-standby capability for seamless failover during maintenance or unforeseen faults. It supports a modular I/O configuration, starting from 8/16 and scalable up to 256 digital I/Os or more through cascading, tailored to project-specific requirements. Communication is fully bidirectional, allowing CU-to-CU and CU-to-FU connectivity with uncompromised speed and performance. The system also features hot-swappable processor modules, live-replaceable without downtime, and supports distributed redundancy, enabling deployment of processors at separate locations without affecting safety. For added flexibility, the Central Unit can even be installed in field location boxes, making it ideal for space-constrained or emergency deployments.​​​
FN-Mux Central Unit
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FN-Mux operate on a fail-safe 2oo2x2 architecture, fully compliant with CENELEC SIL-4 requirements
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FN-Mux offers hot-standby capability, ensuring enhanced system reliability with seamless failover during maintenance or unexpected failures
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Accommodate a minimum of 8/16 digital I/Os, scalable up to 256 I/Os or more, as per project or purchaser requirements, through cascading of multiple FN-Mux digital systems
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Communicate bidirectionally—from CU to CU and CU to multiple FUs—without compromising latency or performance
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Support hot-swappable processor modules, allowing for live replacements without system shutdown
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Enable geographically distributed redundancy, with redundant processors placed at separate, independent locations without any impact on safety or functionality
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Be optionally installed within field location boxes in emergency or space-constrained scenarios.
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Even in the event of complete redundancy removal, the system maintains its SIL-4 safety integrity, offering uncompromising operational security.
FN-Mux Input / Output Structures (in CU & FU)
FN-Mux Input Structure
FN-Mux Output Structure
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​FN-Mux Field Unit (FU) – Intelligent Edge Connectivity
Designed for rugged environments, the Field Unit is the remote interface for vital I/O transmission from field and trackside locations.
The Field Unit (FU) serves as the critical interface for decentralised I/O operations within the railway signalling network. Engineered for harsh environments and compact installations, each FU is built on a CENELEC SIL-4 certified fail-safe architecture, supporting 8 or 16 digital I/Os, scalable as required. Housed in a rugged metallic enclosure, it is ideal for field location box integration and offers flexible mounting options, including DIN rail compatibility. With an integrated industrial-grade power supply and Ethernet switch, the FU ensures secure, real-time communication with the Central Unit—enabling a streamlined, resilient, and high-performance signalling system.​​
Safety Certifications & RDSO Approval
Key Advantages of FN-Mux
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​FN-Mux isn’t just a replacement— but it’s a huge technological leap involving many large technological improvements. Here’s what makes it the smarter alternative:
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Dual Redundancy with SIL-4 Safety: Engineered with a robust 2oo2 x 2 CPU architecture, the FN-Mux is a CENELEC SIL-4 certified system that guarantees continuous, fail-safe operation across all equipment layers. Its advanced hot-standby configuration with hot-swappable modules ensures uninterrupted functionality, even during maintenance or fault conditions—delivering absolute reliability and complete confidence for railway operators.
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Protocol & Platform Versatility: The FN-Mux is fully multi-protocol enabled, offering seamless integration with modern signalling and control systems. It interfaces effortlessly with protocols such as EULYNX, FSE, RaSTA, Modbus/TCP, Ethernet/IP and OPC, and is fully adaptable for railway applications like KAVACH, TCAS, or CTC/TMS, subject to user preference or regulatory approval. Whether deployed as a remote I/O node in the field or installed within relay rooms, FN-Mux flexes to fit operational demands with ease
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Outdoor-Ready and Space-Saving: While the system is primarily designed for indoor installation, the FN-Mux is fully compliant with EN50155 and EN50121-4, making it equally suitable for outdoor deployment. When housed in an IP65-rated weatherproof enclosure, it can be pole- or wall-mounted, for direct signal or point driving uses, thus effectively removing the need for large, masonry signal huts—particularly in remote IBS or ABS locations. Its low power consumption also makes it ideal for solar-powered and backup-supported installations, offering a truly versatile and infrastructure-light solution.
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Integration of Non-Vital Display: In addition to exchanging vital signalling data, the system is also equipped to collect and transmit non-vital information, such as Auto Signalling status displays, both locally and at centralized control centers. This data can be securely conveyed via the Railway’s communication network or cloud infrastructure, using industry-standard protocols like Modbus/TCP, Ethernet/IP, or OPC, ensuring seamless integration with existing SCADA, CTC, or TMS platforms
Downloads
Production Presentation on Fail-Safe Network Mux (as per RDSO/SPN/211/2022 Ver. 1.0)
RDSO Approval Certificate of Fail-Safe Network Mux (as per RDSO/SPN/211/2022 Ver. 1.0)
CENELEC SIL-4 Certificate of Fail-Safe Network Mux (Model: PSS4000-G2 Rail)