Realising robust mission critical networks
Design and maintenance of converged networks in mission critical applications
A mission critical application is an application in which an infrastructure failure may result in serious issues, damage or even loss of life. Examples are public security, traffic monitoring and control, airport and railway infrastructure and many more. The network infrastructure of a mission critical application should operate 24/7/365, often in harsh environments, where operation can be affected by many factors, such as temperature, vibration, interference from neighbouring systems, or lack of ventilation. As network technology develops to accommodate current demands, more devices and systems in mission critical networks are being integrated onto a single converged network. More devices need to be connected, whilst continuing to meet the needs of mission critical systems.
Availability, uninterrupted data transmission and security are essential. The first step in finding the best solution for realising this is defining the network topology. In fact, without first determining the appropriate redundant topology, there’s no point in designing a network. Choosing the right redundancy protocols helps reduce failure risk. Power redundancy also needs to be considered. If a link goes down, the system should continue without impaired functionality or rebooting devices.
The choice of protocol depends on specific network needs. However, whichever protocol is chosen, it is vital these are standardised and supported by different vendors, to ensure proper operation and avoid vendor lock-in. It is important to note that typical redundancy protocols such as RSTP and MSTP are not acceptable for many mission critical applications because of the long network reconfiguration time and dependency on a number of switches in a network segment. MRP (IEC 62439-2) is a better solution, which offers a guaranteed and much shorter reconfiguration - time typically lower than 20ms.
However, some applications, for example in Smart Grids / utilities, industrial automation and transport infrastructure, have even stricter requirements. These require no data loss and no reconfiguration time for the many critical network segments. HSR (High-Availability and Seamless Redundancy) and PRP (Parallel Redundancy Protocol) - the most reliable protocols for critical infrastructures - provide zero reconfiguration time as well as zero packet loss in case of a failure in (the most critical parts of) a redundant network. These protocols are described in the IEC 62439-3 standard.
Industry-related standards strongly recommend using HSR and PRP protocols for the most critical infrastructure segments. One example is Smart Grids, which rely on IEC 61850, the international standard that defines requirements for data communication on Ethernet networks and all connected IP-based devices. This standard strongly recommends using the HSR protocol for station bus applications, in which no reconfiguration time or data loss can be tolerated.
Building a network using equipment from different vendors is standard practice for many mission critical applications - a vendor might not have a product offering for harsh environments, for example, certain technology features might be lacking from their products, or they might not meet the required specifications in areas such as temperature ranges or standards compliance.
Interoperability between different devices is a critical aspect of many applications. Smart Grids are a good example of this: these rely on IEC 61850, the international standard defining digital communication requirements for power utility automation. IEC 61850 defines Ethernet as the basis for all digital communications and lists a wide range of requirements, including data modelling and classes, abstract communication service, substation communication language and many other functionalities. This allows electrical grid owners to build modern, effective and reliable infrastructures using a standardized method of communication as well as standardized equipment from multiple vendors, from end devices and systems, to data networks, SCADA and so on.
Redundancy and interoperability are just two factors out of the many related to mission critical applications, such as security, maintenance, data collection and analysis. Mission critical applications need to meet much higher requirements, as the cost of errors and flaws is much higher. Many of these can be avoided, such as high expenditure on upgrades or downtime as a result of choosing office grade equipment for heavy-duty applications, false port provisioning, or selecting incompatible vendor solutions. Considering the complexity of the issues, when in doubt, consult an expert. We are always happy to discuss your specific situation and requirements!
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