Ethernet as a Backbone for Lighting
Introduction
Ethernet is a high performance and reliable networking technology that has been making inroads into architectural LED lighting applications. Having undergone decades of research and development as a workhorse of the IT industry, Ethernet brings a refined pedigree to a lighting industry which is trending toward highly intelligent light fixtures and services. In this article, we highlight how Ethernet can simplify some of the ways we think about our lighting infrastructure, how its expansive scalability can allow lighting designers to express the full breadth of their imaginations, and how its familiar components can make installation and network upkeep straightforward and manageable.
Why the Networking Onion Matters
The term "Ethernet" refers to two of seven layers that together comprise a stack of independent technologies. This idea of a layered stack is a key feature of a networked system because it allows application designers to ignore the details of the lower layers in the stack. This frees up resources which can then be focused on the intricacies of the application itself, rather than requiring an understanding of the physics of how data propagates on a cable. Ethernet is a specification for the Physical and Data Link Layers of a typical networking stack, governing the cable characteristics and the rudimentary framing sequences that separate the data in each packet.
Figure 1: The Open Systems Interconnection (OSI) Model is a conceptual model of network technology abstraction. It is an example of how disparate systems might organize their networking in order to improve their interoperability.
Layers can often be interchanged. For example, an application built on top of Ethernet can very simply be ported to WiFi equipment, wherein the Ethernet layers get replaced with WiFi layers. The application doesn't need to know that the change occurred.
Layers are frequently encapsulated within one another for routing purposes. For example, a DMX/RDM packet used to communicate with lighting equipment can either be transmitted directly onto an RS485 bus, or it could be encapsulated within an Art-Net packet and transmitted over Ethernet.
Layers can sometimes be combined in ways to enhance security or reliability. For example, Datagram Transport Layer Security (DTLS) is a Transport Layer protocol that adds encryption to the protocols it encapsulates. This in turn adds tamper and forgery protection to protocols that may not have those cryptographic features built in.
Ethernet is a cornerstone upon which this highly flexible layered networking stack is built. For the end user, it enables rich user experiences and ease of use. For the vendor, it enables scalability and wide compatibility with third-party infrastructure.
Ethernet Features at a Glance
An Ethernet cable is an inexpensive commodity that can be found on shelves all over the world. It is easily sourced, and it is very familiar to anyone with proximity to the IT industry. Its connectors are universal, reliable, keyed, and latching, with cables that can be cut to length and terminated in the field with simple tools.
An Ethernet network uses switches to connect different network segments to one another. These switches manage the flow of packets in and out of their ports, preventing collisions that would have otherwise occurred if two devices had tried to transmit packets simultaneously on the same wire. Switches also ensure that packets are delivered precisely according to their destination addresses. Without this feature, the network's security would be compromised because each client would be able to eavesdrop on messages intended for any other client. Additionally, because the switch ensures that packets only go where they are intended, each client does not need to do additional work to inspect and drop packets that it does not necessarily care about, and the overall computation effort of the network remains low.
Ethernet networks are easily bridged into other Ethernet or non-Ethernet networks using off-the-shelf products. This feature enables many different scenarios, such as mixing wired and wireless networks to reach places where it may be difficult to pull cable, centralizing network management, or granting remote access for offsite debugging. Copper Ethernet cabling may also be trivially converted into fiber Ethernet for applications that require extremely long cable runs with low latencies, allowing Ethernet networks to reach distances far beyond what is possible with traditional RS485-based networking.
Ethernet networks can host a variety of unrelated devices at the same time, which can be convenient for modern buildings with heavy reliance on other networked systems. VoIP phones, building management systems, lighting, and employee workstations can all easily coexist on the same Ethernet network, allowing cost and management of the network to be consolidated and simplified.
Ethernet as a Backbone for Lighting
Figure 2: A typical Ethernet lighting network contains traditional network equipment and gateways that convert data into a format that can be natively understood by the fixtures (in this case DMX/RDM).
Modern Ethernet-based lighting protocols, such as Streaming ACN (sACN) or Art-Net, are designed to encapsulate older stalwart lighting protocols such as DMX and RDM. Modern protocols apply the advantages of Ethernet technology to lighting networks and can dramatically improve some of the limitations and inflexibility of the aging DMX/RDM.
Network Installation
Traditional DMX/RDM RS485-based networks can be error prone. When designing a DMX/RDM lighting network, the system architect must be acutely aware of many low-level details that may not be of interest or apparent. For example, the DMX/RDM ecosystem contains a variety of incompatible connector types, ranging from XLR connectors, to proprietary connectors, to bare leads and screw terminals. The cable types are not tightly specified, and the available cable varieties must remain compatible with the connectors in use. Electrical noise resistance and bus loading can be hard to characterize and understand. A terminating resistor must typically be manually attached to the end of a DMX/RDM bus which may not be easily accessible. Between the variety of interconnection options and the signal integrity risks in real-world installations, there can be many headaches.
Ethernet network installation is typically a more straightforward activity and doesn't require any exotic or hard-to-find equipment. Essentially all copper Ethernet cable types use RJ45 (8P8C) connectors, and at the most common network speeds of 10/100/1000Mbit/s, Category 5e or better cable will work. Cables can be bought at any length with molded connectors and strain relief, or they can be cut to length and terminated in the field with common tools. Ethernet jacks often sport built-in indicator LEDs that give immediate feedback about whether a network link is active and working, allowing field technicians to quickly verify whether the cable is properly installed without having to use complicated software or equipment. Ethernet is always electrically isolated, meaning that regardless of the electrical conditions experienced at each device, there is no risk of grounding issues that could affect safety or reliability.
Figure 3: Within this example, a set of office downlights can be controlled and monitored remotely. Wired and wireless clients can be given access to control and monitoring data as desired. At the same time, other devices connected to the Ethernet switch (like Printers and Phones) are not only electrically isolated from the office downlights, but they also can be configured in such a way to not receive lighting specific data.
Universe Addressability
Ethernet brings a massive increase in addressability to lighting networks, with sACN supporting up to 63,999 universes (512 channels each) and Art-Net supporting up to 32,768 universes. This frees the lighting designer to manage universes in ways that weren't previously feasible. For example, they could optimize for their controller's cost structure (if they pay per universe), logically group certain lighting products in different universes ; based on their physical location, create dynamic shows instead of static shows, and so on.
Multi-master Controls
sACN supports DMX stream prioritization. More than one controller may be active at any given time, but only the highest priority controller will be allowed to manage the lights. Prioritization can be used in a simple failover strategy with a backup controller that transmits at a lower priority than the primary controller. Similarly, multiple Art-Net controllers can be used to manage, monitor, and control the same lighting products simultaneously, or even monitor each other to detect controller failure and recover on the fly.
High Performance
A sACN packet is fully transmitted in about 55 microseconds on a 100Mbit/s Ethernet link. This means that roughly 600 universes of 512 channels each can be smoothly updated at 30 frames per second simultaneously over a single Ethernet link, or ten times that if a gigabit Ethernet link is used. With more than 600 times the performance of traditional DMX, Ethernet can unlock some awesome creative possibilities on a grand scale.
Furthermore, sACN (though not Art-Net) supports IP multicasting, which is a packet addressing technique that lets lighting fixtures "subscribe" only to the universes that they are interested in receiving. The Ethernet switches maintain these subscriptions, reducing the amount of work needed by the lighting controller by enabling a "one to many" addressing scheme. The controller can send a single packet addressed to a single universe, and only the fixtures subscribed to that universe will receive it. In comparison with the multicast addressing technique, a unicasted packet is "one to one," requiring the controller to send one packet to every lighting device, and a broadcasted packet is "one to all," which only requires one packet from the controller but requires all the lighting fixtures to inspect that packet to determine whether it should be processed. Multicasting reduces the amount of work done by both the fixtures and controllers and cuts down on overall network congestion.
Monitoring
For cost and size reasons, lighting products are typically embedded with electronic devices that possess a limited amount of onboard data storage. On their own, these types of products would not be able to sustain long-term monitoring tasks, but when coupled with an Ethernet network and a monitoring server that can periodically retrieve information, the lighting devices form a swarm of simple nodes that can gather and report data to a more sophisticated centralized monitoring service. Monitoring services are able to store and organize huge amounts of data, and can detect outages, visualize trends, discover usage patterns, and so on. In today's highly connected society, data is a valuable commodity, and Ethernet-enabled devices and networks allow end users to extract the value from their data.
Lumenpulse: Committed to Ethernet
The smart Ethernet-enabled products in the Lumenpulse portfolio allow customers to leverage the many advantages of this modern networking technology, delivering convenience, performance, and flexibility to lighting jobs both large and small. Lumenpulse's commitment to Ethernet as a backbone for modern lighting systems has advantages for designers, contractors, building management, and field service personnel. Ethernet's ubiquity, performance, and proven success in the IT industry brings the confidence that it will remain available and supported for decades to come, making it the clear choice for today's increasingly demanding architectural LED lighting applications.