STATION REFURBISHMENT DIGITAL RAILWAY
Digital Metro Ambitions Need Critical Connectivity Metro/urban railways are turning to the wide area network and the transformative role a multi-service WAN can play in making smart rail goals a reality
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s more and more of the world’s population gravitates to urban areas, the pressure intensifies to revolutionise the rail experience. Increased numbers of riders, trains and security issues have urban rail operators looking for ways to be more dynamic and reliable, and to keep passengers and rail assets more secure. One way to satisfy these ambitions is to adopt digital era technologies. Video analytics, predictive maintenance, communications-based train control (CBTC), and AI are all key technologies in this transit revolution. While connectivity is the reason communications networks exist, it’s also the essential thing that rail operators need to fully and successfully embrace digitalisation. That is, a smart metro relies on sensors to collect critical data and on a communications network to transmit those billions of bits and bytes in real time for analysis. This requires seamless connectivity, underpinning a constant stream of data between tracks, trains, stations, operations control centres and data centres. Such connectivity makes a missioncritical wide area network (WAN) crucial to the strategy. Indeed, an Internet Protocol Multi-Protocol Label Switching (IP/MPLS) and segment routing multi-service WAN will deliver ultra-high reliability, performance and security with bandwidth that feels like it will never run out. Plus, the WAN offers the flexibility to support a wide range of applications, both new and legacy, down to each application’s individual operational requirements.
The mission-critical WAN
The primary role of the WAN in a digital urban rail infrastructure is to connect all physical and digital infrastructure elements. It’s a multilayer converged network that deploys IP/MPLS and segment routing over a mix of dark fibre and packet optical transport. 54
But, what happens when IP-based applications such as CBTC, IoT and CCTV are introduced into the network and must be managed alongside older SCADA and wireless applications, some of which may still operate with legal serial and four-wire analog interfaces? Multiservice support becomes critical, as these Layer 2 and Layer 3 network services connect the trackside equipment and sensor endpoints, and do so at very high scale. Additionally, IP multicast capabilities must be supported for the point-to-multipoint distribution that optimal video surveillance requires. Beyond scale and service diversity, resiliency is also critical because no one wants a disruption in the WAN that disrupts train operations as well. IP and segment routing MPLS multi-layer and multi-fault redundancy protection will mitigate the risk, even during extreme weather events or in the event of a deliberate sabotage of the installed fibre. Flexibility to support strict requirements around latency and lossless networking will also be essential. Deterministic Quality of Service (QoS) down to the application level will help operators constantly meet expectations even when the network is super congested. Time synchronisation distribution will also matter. As 5G small cells are deployed along tunnels, synchronisation challenges are amplified because timing information must be transmitted across the WAN. That’s why support for a flexible hybrid approach is needed. This will combine Global Navigation Satellite System (GNSS)-derived timing and IEEE 1588 Precision Time Protocol (PTP) with boundary clock capabilities for accurate timing distribution throughout the network. While this series of capabilities is fundamental to the mission-critical WAN, there are other ways in which an IP and segment routing MPLS-based WAN delivers the bandwidth, availability, flexibility and advanced tools to support a successful digital metro.
One example is segment routing. Fast emerging as the de facto standard in IP networks, segment routing reduces protocol complexity and can simplify operations and support scaling even in networks with hundreds of nodes. Ethernet virtual private networks (EVPNs) are also key. Amping up efficiency and redundancy, EVPNs provide reliable Layer 2 services that are essential for applications like signalling. Traffic engineering is also pivotal to safety-critical systems. The blue/red redundancy model enables data routing along separate paths. Even in a situation where a node or link fails, the two channels cannot be affected at the same time.
The OT cloud
In a smart rail system, where intelligent software systems control, manage and monitor infrastructure and operations, one needs seamless connections within data centres. That’s where the operational technology (OT) cloud comes into play. OT typically sits within a private cloud that is most often on premises, or hosted in a dedicated data centre, purpose-built for rail operations. Other than CBTC, which maintains its own set of dedicated servers to meet safety and certification requirements, there are substantial advantages to running critical smart rail applications in the OT cloud. One advantage is the opportunity to pool compute, storage and memory resources. So, systems like SCADA, CCTV and passenger information can be hosted more efficiently within the OT cloud with embedded redundancy and improved resource utilisation. There are also smoother upgrade cycles using digital twins, helping operators respond to change without compromising reliability. While the mission-critical WAN forms the backbone of digital rail, the OT cloud can extend that reliability, flexibility and resilience into the data centre, guaranteeing