Korenix enables CCTV and WiFi services for onboard rail applications
Ensuring maximum availability of security and surveillance systems, as well as passenger infotainment services, Power over Ethernet (PoE) and Power over Ethernet Plus (PoE+) devices enable cost effective deployment, operation and maintenance.
Bringing the latest security and surveillance systems (e.g. CCTV), as well as onboard entertainment technologies (Infotainment) such as passenger display screens and WiFi services, to the demanding rail sector is a challenge. Reliability of these onboard technologies is critical for both train operators and passengers, while also improving the maintenance of onboard devices when trains are on the move.
Factors to Consider: PoE/PoE+
Today, as more data is being used and demanded from rail operated services and for passenger requirements, a Gigabit backbone of the core train network is now typically required for these products and services. This backbone is perfect for providing onboard CCTV and WiFi services.
For network hardware such as Ethernet managed switches and end devices (CCTV cameras, Infotainment displays, WiFi technologies, etc.) it is important to consider the IEEE standards relating to Power-over-Ethernet (PoE), as some hardware manufacturers provide non-standard versions. The original IEEE standard for PoE devices is designated as 802.3af normal PoE maximum 15.4Watts per port. However, this power rating may not be sufficient for the latest high power cameras, particularly the units that offer PTZ (pan-tilt-zoom) functionality. Many IP cameras now have integral motors and drives or other features such as fans or heaters.
Some switch manufacturers may only offer units that satisfy the normal PoE power standard (i.e. 15.4Watts), which may not be sufficient. The latest IEEE standard is designated as 802.3at High power (or PoE+) maximum 30Watts per port. PoE+ therefore allows more powerful PTZ cameras and other onboard Infotainment technologies to be deployed.
Even if an existing rail carriage network already has a variety of non-PoE switches installed, the IEEE POE+ standard specifies that plugging in a non-PoE unit to the network will not harm this device as power is not sent until the switch (Power Sourcing Equipment) and the end device (PD powered device) have confirmed via an ‘automatic system check’ that PoE is actually required by the device.
Another key benefit of deploying PoE/PoE+ switches is that deployment costs are reduced, as additional cable runs are not required throughout the carriages. This also reduces the total weight of cabling, which contributes to improved fuel efficiency of the train. Cable looms are very expensive and so anything that can be done to reduce the amount of cabling required and the space needed for ducting of cables under carriage floors and overhead, is attractive to a rail operator.
If a train is currently taken out of service for a routine maintenance check after a set number of hours, by deploying managed switches, this service interval can be increased and savings made by monitoring onboard equipment and systems. An example is the deployment of a managed switch to monitor a rail carriage door system, a safety-critical system. Early indications of wear or impending component failures can be reported early and any remedial action taken in plenty of time before the door system fails completely forcing the train to be taken out of service.
Other advantages of PoE/PoE+ switches are that they offer a variety of manageable features, including:
• Power Device ‘Keep Alive’ Check – a managed switch periodically communicates with end devices in order to check they are OK. If it doesn’t respond, the switch waits, then cuts off the power and reboots the end device, before flagging this action up to the operator, who may wish to investigate further. Automatically rebooting a camera or WiFi device can save considerable time and costs by not having to physically send an engineer to the camera location to unplug/plug in the device.
• Power Scheduling – the system can be set up to schedule provision of power to end devices, which can be switched off at certain times of the day when they are not needed. For example, a security camera may be required as a safety system for the train station platform operator, who needs to be alerted as the train approaches the platform. The driver may also require similar onboard CCTV cameras to provide a view of the complete length of the platform as the train arrives and departs. At other times, when they are not required, these cameras can be switched off.
• Power Priority – if there is a power drop on the network or emergency back-up power is required, the system can be set up to provide power to only the most critical end devices on the train.
All switches should be certified to the relevant European Rail standards, i.e. EN50155 and EN50121-4. In addition, the following factors must be carefully considered before selecting a suitable supplier of managed switches:
Most rolling stock and rail projects require an extended unit shelf life of 15 years or more. Industrial, ruggedized switches should therefore be selected on the basis that they would satisfy this extended product lifecycle and allow the train operator to fit-and-forget” these switches. This also means that any hardware spares (and product software updates) must be available throughout this extended period.
When selecting a suitable switch for a rail application, vibration is another critical factor to consider. This is important as the switches may be installed close to a railway line. The vibration from trains travelling past 24/7 is therefore often sufficient to break any standard device within a short period of time. Similarly, if the switches are installed onboard a train, they will have to withstand the high vibrations from the engine and from the continual movements of the carriages as they travel along the track.
Almost all onboard systems have issues with either loose connections or internal components failing due to high vibrations, typically after only a couple of years of service. It is therefore recommended that switches are mounted with M12 Ethernet connectors as the emerging standard for on rail communications. This will prevent vibration damage to both the cable ends and switch ports, ensuring constant connection throughout the product lifecycle.
In train security and surveillance applications, as well as onboard passenger Infotainment systems, typically at least one managed switch is located in each carriage or in a junction box at the trackside, with other switches installed at the point of the CCTV camera. Here, a key factor to consider is the temperature rating of the switch. Most switches operate between 0°C and +40°C. However, over the past few years, temperatures across Europe and the UK have been pushing towards new record highs, with summer temperatures in the high 30s and winter temperatures as low as -20°C, particularly in the more rural locations. In these environments, ruggedized switches need to be deployed. Designed from the component up, these switches typically offer operating temperatures of -40°C to +75°C, although this will vary from one switch manufacturer to another. These switches have typically undergone rigorous specialist testing to ensure that they can operate reliably at these extreme temperatures.
Unlike most industrial environments, on a train, availability of power is much less reliable and is more prone to spikes and voltage drops. This means that most rail devices including switches require a very wide operating range in order to ensure not only continued operation, but also to prevent damage to the equipment. For example, on train engine start-up, power is often cut off completely to the switches initially and then put on again after a short period of time. Switches must be designed to cope with this fluctuating availability of power.
Typically, if a switch is deployed on a main power line of a train, even though the switch is rated at 110V DC, it may be required to operate over a very wide voltage range of between 77V and 137V DC.
Some rail operators are still considering the use of older, unmanaged switches for onboard train solutions. While these switches can seem more cost effective in the short term (due to their lower unit cost), over the long term, new applications will be identified that will almost certainly require managed switches to be installed, which means that twice the investment will be needed.
Unmanaged Ethernet networks do not have the variety of data management and security features such as VLAN, QoS and IGMP (see below in ‘software’). These are used to ensure security of data between different vendors sharing the network. These types of features enable priority to be given to certain types of data traffic over the network. For example, vendor systems that are either safety-critical or provide high security data can be given higher priority than other vendor systems over the network. Also, in the case of video surveillance applications, managed switches also provide features that prevent network storms, which can interrupt the reliable operation of safety-critical surveillance cameras.
All managed switches should operate on ‘open’ connectivity standards, allowing for complete interoperability with other products and vendors. Switches should be provided with software that allows full configuration into any network topology. As with all software, patches and bug fixes are required from time to time. These are standard across all reputable switch manufacturer ranges and are typically provided free-of-charge to customers. Allowing software updates also offers the opportunity of providing rail operators with new additional features to an existing hardware platform as these are developed over time, which is critical if the devices are required to operate reliably over an extended life of 15 years.
Switches should also be supplied with built-in protocols (switch ports) such as VLANs (Virtual Local Area Networks) to allow multiple companies/vendors to share the same physical network/backbone installed on the train, while simultaneously ensuring full separation of data.
Managed switches also enable detailed reporting of network activity, allowing for maintenance to inspect what has been happening to a particular onboard device over time and ensuring the correct product support
Designed for harsh industrial environments, ruggedized Ethernet managed switches like the Korenix JetNet 6710G have the ability to check the connectivity status of the attached device.
If the device becomes unresponsive, it can be automatically restarted and a desired notification of the incident is then sent to the requested parties. This type of solution allows for the first-line support step to be carried out regardless of the location or time of the incident and the corresponding alerts can be tracked in order to build a clearer picture of whether a particular device or unit is in need of repair or maintenance, and if so, the appropriate scheduled maintenance can be arranged, without the train having to be removed from the track.
For more information, visit the JetNet 6710G Series product page
Author: Korenix Technology / Garth Miller Published: 19 Nov 2014