Powering Communication and Seamless Digital Rail Operations
As our urban populations expand, metro-urban railways must adapt to meet the surging demand. This growth requires operators to modernize their infrastructure with smart digital innovations and cutting-edge technologies.
Recent data from the United Nations shows that by 2050, approximately 68% of the global population will reside in urban areas, marking a significant increase from the 55% recorded in 2018 – a net growth of 2.5 billion people. As the population of cities increases, so does the demand for reliable and efficient public transportation. To effectively serve the escalating number of commuters, metro-urban railway operators must enhance transport capacity, improve service reliability, and prioritize passenger safety.
Many operators are embracing the digital rail paradigm to address these challenges, adopting a wide array of digital applications integrated throughout their infrastructure.
These applications include various safety-focused communications-based train control (CBTC) systems, operation-critical Internet of Things (IoT) sensors, and passenger-centric amenities such as essential real-time information services and Wi-Fi connectivity. By integrating these digital technologies, railway operators can create a more efficient, responsive, and passenger-friendly travel experience while adapting to the evolving landscape of urban transportation.
The Nokia Train-to-Ground solution offers a comprehensive and innovative approach to tackling the challenges of a rapidly growing urban landscape, and by adopting this solution, operators can explore a new era of railway connectivity and optimize their operations with real-time data insights and smart communication.
For digital rail systems to operate seamlessly, they require a robust, efficient, and secure communications network infrastructure that connects all application subsystems and components throughout the railway system. Numerous applications within this setup are sensitive to delays or require substantial bandwidth, leading to significant demands on the overall network infrastructure, especially on the train-to-ground network. Maintaining the reliability and performance of this network becomes essential to ensure the smooth functioning of various critical operations within the digital rail ecosystem.
The train-to-ground network is a comprehensive communications network encompassing the connection between the train and the ground (track) and extending further to the operations control center (OCC). This extensive network is responsible for transmitting all the onboard application data, making it a critical component of the digital rail system.
However, the network faces challenges due to the constraints of limited bandwidth at its wireless link and inherent vulnerabilities in the radio links. Addressing these issues is paramount to ensuring a reliable, efficient, and secure train-to-ground communication system capable of meeting the demands of modern digital rail operations.
Traditional Train-to-Ground Networks Present Challenges
Rethinking the train-to-ground network is integral to overcoming the challenges posed by traditional approaches. Historically, railway operators have employed separate, purpose-built train-to-ground networks for different onboard applications, resulting in a disjointed system. For example, CBTC and CCTV would utilize separate Wi-Fi networks, while voice communications relied on a land mobile radio (LMR) network. These radio technologies are often proprietary, lack interoperability, and – in many cases – are nearing obsolescence.
The traditional approach has led to high operational costs and significant maintenance efforts and impedes digital innovation as it lacks scalability for future applications. Therefore, this model requires a shift, prompting operators to adopt a new train-to-ground network architecture that supports existing digital applications. Its ability to scale for both growth and accommodate new technologies is future-proof.
Moving away from application-specific networks to a converged architecture allows for tailored, segregated network services on an onboard mobile access router (MAR) catering to each rail application’s distinct quality of service (QoS) demands.
Ensuring resilience in the train-to-ground network is crucial, especially when considering safety-critical applications. A network outage affecting such critical systems could disrupt or even stop train services, leading to passenger inconvenience, economic losses, and damage to a city’s reputation. To achieve this resiliency, operators must design and deploy the network with extensive redundancy protection throughout the communication paths across multiple domains.
By embracing this new train-to-ground network architecture, operators can optimize current digital applications and future-proof their systems to accommodate emerging technologies. This strategic shift will facilitate the rapid adoption of the digital rail paradigm, enabling smoother operations, enhanced safety, and improved passenger experiences.
Reliable Data Delivery
Ensuring reliable data delivery poses a challenge for the train-to-ground network, given its limited bandwidth compared to fiber networks. Constantly delivering data with high quality of service (QoS) becomes more difficult, and the network must adapt to occasional radio link performance issues caused by fading or interference. To address this, a smart, self-adapting QoS algorithm is essential to guarantee the assured delivery of data.
Robust Security
As digital transformation becomes more prevalent in rail operations, the widespread use of information and communications technology (ICT) introduces new vulnerabilities and expands the attack surface making cybersecurity a top priority. Operators must safeguard the entire rail infrastructure, protecting the train-to-ground network from attacks. Implementing robust cybersecurity measures is crucial to maintaining the system’s integrity and security.
Real-Time, Scalable Network Management
Given the high number of trains in motion, managing and monitoring numerous train-to-ground communication sessions simultaneously requires a scalable network management system. This system is essential in providing operators with a comprehensive real-time view of the entire fleet, enabling effective control and oversight.
Future Proof
The ever-advancing fields of big data, artificial intelligence (AI), and machine learning have created promising opportunities for the rail industry. By harnessing the capabilities of ICT, rail operators can continue their digital transformation journey and leverage these technologies to meet future needs efficiently. Embracing the latest advancements allows for enhanced efficiency, improved decision-making processes, and better overall performance in the rapidly evolving landscape of rail transportation.
Nokia’s Innovative Train-to-Ground Solution
Nokia’s response to the train-to-ground architecture challenge entails a unified and comprehensive network solution. Designed with a service-centric architecture, the Nokia Train-to-Ground solution offers extensive multiservice capabilities to accommodate various applications. Through resilient, reliable, and secure broadband communications, it establishes seamless connectivity between onboard equipment and the Operations Control Center (OCC).
The solution blueprint comprises three distinct architectural layers:
Service Layer
At the top level, the service layer is the backbone, delivering end-to-end routing services. This layer efficiently manages unique, multi-path traffic flows specially provisioned between the Mobile Access Router (MAR) and the tunnel server. The MAR provides segregated and customized network services for all onboard applications and equipment.
Through unique IP subnets and protocol types like TCP or UDP, onboard traffic receives prioritization based on the assigned type of service, ensuring critical services receive the highest priority. The data is encapsulated within an IP tunnel and transmitted over one or more radio links (LTE/Wi-Fi) managed by Nokia’s multi-path connectivity software.
Once the data reaches the tunnel server, the IP tunnel is terminated, and the traffic is routed to application servers in the Operations Control Center (OCC), data centers, and other parts of the rail infrastructure.
Wireless Access Layer with LTE
The middle layer of the architecture involves the wireless access layer that harnesses the power of LTE technology. This layer facilitates high-speed wireless communication and ensures a seamless and efficient data transfer between the onboard equipment and the central network, encompassing an LTE path that extends from the train to the trackside and connects to the core system in the OCC.
This private LTE (PLTE) system consists of LTE base stations called eNodeBs (eNBs) strategically deployed throughout the rail system, facilitating the connection between LTE user equipment (such as the MAR) and the core. In cases where deploying a PLTE system is impractical, alternative options include using a Wi-Fi network or a commercial LTE service as a backup system to the PLTE setup.
Backhaul Transport Layer
Finally, the backhaul transport layer is the foundation of the Nokia Train-to-Ground solution. It handles reliable data transport between the wireless access points and the central network infrastructure, ensuring robust connectivity and data integrity throughout the entire train-to-ground network.
The transport layer is established as a private IP/MPLS backbone network that not only provides LTE backhaul service – connecting all eNBs to the LTE core – but also offers advanced capabilities such as flexible Layer 2 and Layer 3 network services, deterministic Quality of Service (QoS), multi-fault resiliency, and robust security. Additionally, it ensures efficient connectivity between various trackside devices and in-station equipment without compromising train-to-ground backhaul performance.
Solution Capabilities
Multiservice
The Nokia Train-to-Ground solution encompasses a range of capabilities, including multiservice support facilitated by the MAR and its multi-network aggregation manager (MNAM). The MAR is the gateway for all onboard applications, offering versatile network services through virtual LANs (VLANs) segregating data. VLAN traffic is prioritized, encapsulated within an IP tunnel, and transmitted via aggregated wireless links.
By implementing the MNAM, the Train-to-Ground solution achieves efficient data management, ensuring each application’s traffic receives dedicated handling and prioritization throughout the network. This segmentation allows for a more seamless and robust communication process, enhancing overall system performance and delivering a superior user experience for railway operators and passengers.
Multi-Fault Resiliency
Ensuring multi-fault resiliency is crucial in the train-to-ground network because it carries safety-critical and operation-critical data. For network operators, maintaining highly reliable train service is vital. A single link or component failure along the communication path can disrupt communications, significantly impacting train services. Therefore, the train-to-ground network needs to incorporate a comprehensive set of robust redundancy protection mechanisms to withstand multi-fault failure scenarios effectively.
The key elements in the end-to-end protection are:
- MAR redundancy pair
- Multi-network/multi-path radio link aggregation
- eNB redundancy pair
- Resilient IP/MPLS backhaul
- LTE core redundancy pair
- Tunnel server (TS) redundancy pair
- OCC geo-redundancy
MAR Redundancy Pair
The MAR serves as the onboard IP gateway, connecting all onboard equipment. To ensure high-availability IP access, deploying a redundant MAR pair is crucial. In this setup, a standby MAR is ready to assume the role of the active router whenever it detects a failure in the active MAR. This seamless switchover ensures continuous and reliable IP connectivity for onboard applications, even in the event of a failure.
Multi-Network/Multi-Path Radio Link Aggregation
Given the susceptibility of radio links to interference and performance degradation, employing a multi-network/multi-path approach is essential for building a redundancy train-to-ground network that can reliably carry onboard data, especially safety-critical data from CBTC. The active MAR connects multiple LTE and Wi-Fi networks, effectively aggregating radio links and distributing data across all available paths.
Additionally, the MNAM aggregates radio links from the hot standby MAR, forming an active-active radio redundant pair. This approach significantly increases the number of available radio links for data transmission. In case of a radio link failure, the MNAM dynamically adapts to minimize impact. The multi-network/multi-path strategy enhances bandwidth capacity, improves utilization, and strengthens overall network resiliency, resulting in better onboard application performance.
eNB Redundancy Pair
The eNB redundancy protection involves two options: colocated and interleaving. In the colocated option, two redundant eNBs are located in the same place along the track, providing nodal redundancy protection. On the other hand, the interleaving option deploys two eNBs in an alternate, interleaving manner along the track, offering both nodal and geo-redundancy protection. The interleaving option, however, requires more installation effort due to the doubled number of installation sites along the track and power distribution points.
Resilient IP/MPLS Backhaul
The backhaul network, responsible for connecting all eNBs with the LTE core, forms the communication foundation of the railway infrastructure. It links all trackside and in-station equipment to the equipment and servers in the OCC and data centers. While IP/MPLS boasts various resiliency capabilities, including nonstop routing, fast reroute, and secondary label-switched path protection, ensuring the backhaul network has rich and diverse connectivity is crucial.
This diversity enables IP/MPLS to reroute data – particularly surveillance video – around multiple failure points, even during major disasters. This is key to retaining situational awareness and maintaining critical services when faced with adverse and emergency scenarios.
Server Redundancy Protection (LTE Core And Tunnel Server)
The LTE core and tunnel server are vital gateway servers responsible for terminating all LTE paths and the corresponding unique, multi-path traffic flow from the MAR. A failure in either of these servers can render train-to-ground communications from all trains out of service, disrupting onboard applications and bringing train services to a complete halt. It’s necessary to support the LTE core and the tunnel server in duplex mode with an active core and a standby core for each of them.
However, traditional duplex mode implementations require re-establishing all communication sessions during protection switching, leading to operational risks and traffic storms. To avoid such disruptions, hot redundancy protection technology ensures that when the active LTE core or tunnel server (or both) fails, the MAR immediately forwards traffic to the standby server(s) without disrupting onboard applications.
OCC Geo-Redundancy
The OCC is the nerve center for rail operations, where operators monitor, control, and analyze the rail system’s operating conditions while responding to incidents. With extreme weather events – such as severe flooding and storms – becoming more intense and frequent, implementing a standby OCC equipped with an identical network and application environment at a different location is crucial. During nonoperational scenarios of the active OCC, all MARs redirect data to the LTE core and tunnel server in the standby OCC, ensuring uninterrupted train services and continuous functionality.
Smart, Application-Aware Quality of Service (QoS)
The MAR goes beyond simple data routing to provide a unique, intelligent, and application-aware QoS scheduler, ensuring reliable and optimal data delivery based on priorities. The MAR classifies IP flows from all onboard applications into distinct priority classes by analyzing various parameters such as VLAN header, protocol number, Differentiated Services Code Point (DSCP), and UDP/TCP ports. This classification enables the MAR to schedule data transmission according to the assigned priority, guaranteeing that critical applications like CBTC receive the utmost attention.
To achieve robust and efficient delivery for vital applications like CBTC, the MAR can replicate CBTC data across all available radio links. When the far-end tunnel server receives the first copy of CBTC data, it immediately forwards it to the application server to minimize the delay. In case of packet loss or corruption during transmission over the primary radio link, the tunnel server swiftly switches to an uncorrupted copy received from other radio links, ensuring the uninterrupted operation of CBTC.
Strong Network Defense
The attack surface expands significantly with the increasing connectivity of railway infrastructure and heavy reliance on Information and Communication Technology (ICT). Common threats include a wide range of cyber and physical attacks that target communication facilities and cables.
Implementing robust network defense mechanisms is essential to protect the railway infrastructure and operations. This involves employing advanced cybersecurity measures, including intrusion detection and prevention systems, firewalls, encryption, and secure communication protocols.
By combining these security measures, the train-to-ground network can effectively detect and mitigate potential threats, ensuring the integrity, confidentiality, and availability of critical data and services.
Segregated VLAN Routing Services
With segregated VLAN routing services, each application’s data is confined to its designated service domain, preventing attackers from moving between different domains laterally. For instance, if an onboard camera is compromised, the attackers cannot use it as a foothold to access the critical CBTC domain. This isolation ensures that any breach in one domain does not jeopardize the security and integrity of others.
The MAR employs standards-based encryption, incorporating a secure socket layer (SSL) and IP security (IPSec) to protect data from eavesdropping and man-in-the-middle attacks. Additionally, dynamic firewall filtering and probe packet insertion further enhance the network’s defenses against potential threats. By combining these security measures with the redundant protection schemes discussed earlier and following security best practices, the converged train-to-ground network forms a robust defense against cyber and physical attacks. This comprehensive approach enables the rail system to operate without compromise, ensuring data confidentiality and system integrity.
Fleet Network Manager (FNM)
The Nokia Fleet Network Manager (FNM) maximizes operations synergy by remotely managing end-to-end train-to-ground communications. Apart from configuration, event, and alarm management, the FNM takes charge of all train-to-ground communications on a fleet level directly from the Operations Control Center (OCC). This management includes real-time data usage tracking, operating statistics, performance information, and support for geo-fencing.
By providing a complete overview of communication service performance for the entire fleet or specific sets of trains, the FNM empowers operators to monitor and optimize network performance efficiently. This centralized management approach enhances operational efficiency, simplifies troubleshooting, and ensures a seamless communication experience across the entire rail fleet.
Evolving Towards the Future
The Nokia Train-to-Ground solution is a flexible platform that seamlessly adopts future technologies. LTE, being an open-standard, globally deployed wireless technology, offers a diverse ecosystem that enriches its use cases. As urban-metro railway operators adopt new applications for better oversight, the LTE network can evolve to support Narrowband IoT (NB-IoT) and LTE for Machines (LTE-M) technologies to connect trackside sensors. Additionally, operators can leverage mission-critical push-to-talk (MC-PTT) and push-to-video (MC-PTV) capabilities to migrate legacy Land Mobile Radio (LMR)-based applications over the train-to-ground network. The LTE system can smoothly transition to support 5G radio technology as operators explore applications with ultra-low latency or high bandwidth demands.
The IP/MPLS backhaul network also has the potential to evolve, allowing for the inclusion of segment routing capabilities that facilitate seamless network-cloud networking in the future. By staying adaptable to emerging technologies, the Nokia Train-to-Ground solution remains future-proof, accommodating the changing needs and demands of urban-metro railway operations.
Putting Everything Together
Figure 13 (below) illustrates the end-to-end journey of onboard CCTV video data that the intelligent Nokia SpaceTime Scene Analytics gateway will analyze.
The data undergoes processing and is “touched” by various network elements throughout the following steps:
- The CCTV camera sends IP video data to the MAR.
- The MAR classifies the application data and utilizes its MNAM capability to optimize transmission over wireless links.
- The eNB receives the wireless data and forwards it to the backhaul IP/MPLS router through an Ethernet interface.
- The router transports the wireless data to the LTE core equipment.
- The LTE core equipment processes the wireless data and routes it to the tunnel server.
- The tunnel server terminates the VPN tunnel and directs the data to the designated SpaceTime Scene Analytics gateway.
- The Scene Analytics gateway analyzes the video data in real-time, detecting anomalies and providing valuable insights.
The efficiency and reliability of this entire process depend on a well-designed, end-to-end train-to-ground network architecture. With a robust architecture in place, the consistent and assured delivery of data to its intended destination is ensured, enabling the smooth operation of various onboard applications.
Download Nokia’s Application Notes on Train to Ground Communications >>
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