The Smart City Blog

BACnet, LonWorks, and HD-PLC: Choosing the Best Open Protocol for Your Building Automation System

The smart building market is evolving quickly. As it does so, facility owners and system integrators need an open protocol for integrating diverse building automation systems (BAS) into a single, comprehensive building management system (BMS) that meets the performance, flexibility and cost requirements of applications today and tomorrow.

Selecting the right open protocol starts with knowing the history, key technical distinctions and ongoing development of available approaches. But it doesn’t end there. One must also understand how smart buildings themselves are changing network architectures and placing new demands on the protocols used therein.

Originally developed approximately 30 years ago, BACnet and LonWorks inspired intense debate amongst building automation professionals in the first decade of the 2000s (the infamous “Protocol Wars”). In the end, there wasn’t a clear winner, and both protocols have enjoyed widespread adoption across HVAC, fire, security, and other building automation systems.

Chances are, your building already employs at least one of these protocols, and you face a difficult decision in deciding whether to extend it or integrate another protocol to meet your future needs. This article will take a look at both of these open protocols, as well as a new one (HD-PLC) that brings a range of benefits to modern smart building control networks.

Illustration of city technology


BACnet, short for Building Automation and Control Network, is an open protocol that was developed by the American Society of Heating, Refrigerating and Air-Conditioning Engineers for building automation and control equipment in the early 1990s. It became an American National Standard (ANSI/ASHRAE 135) in 1995 and an international standard (ISO-16484-5) in 2003.


Given its origin and support by ASHRAE, BACnet has enjoyed the most success in programmable controllers for air conditioning systems, ventilation systems, fume hoods, pumps, and valves. It is also found in lighting, safety and security, and other building automation systems. BACnet is supported by more than 800 manufacturers across hundreds of devices, with millions of installed devices worldwide.

A key distinguishing feature of BACnet is its top-down approach to control networks. Based on a client-server model, BACnet defines a tiered architecture optimized for workstations and head-end computers that need to process and communicate large amounts of data. One of its strength is the standard object-oriented model it uses to represent the functions of devices. Functions such as analog and binary inputs and outputs, alarms, and schedules are represented as “objects” (e.g., an analog input object), each of which has a set of standard properties like present value, alarm thresholds, etc.

Following the client-server model, building automation systems use “service requests” to access a property or request an action from a BACnet object. Service requests are the standardized way that BACnet devices get information, issue commands to perform certain actions, and communicate events to other devices. The protocol defines a standard set of objects, but vendors are free to add new properties to existing object types or create new objects types and add functionality to their devices. This enables manufacturers to differentiate their products, but it can create problems for end customers who may now find themselves locked into a proprietary solution.

Another key consideration for BACnet is that it only uses four of the seven layers of the OSI model, primarily operating in the management and automation layers. Because of this, BACnet systems do not require their own transmission technology and system integrators are free to choose amongst five options to optimize network price and performance. The fastest (and most expensive) is Ethernet, offering speeds up to 100Mbps. Next is ARCNET with speeds up to 2.5Mbps over coax, twisted-pair or fiber optic cables. BACnet also defines an MS/TP network for twisted-pair implementations under 1Mbps. Lastly, it supports LonTalk over a variety of media, as well as point-to-point over phone lines or hardwired EIA 232 connections.

BACnet provides considerable flexibility to facility owners and system integrators—but this comes at a cost. Meeting the bandwidth demands of modern smart building applications typically requires the deployment of costly new wiring infrastructure. With the installed cost of Ethernet estimated at $300 per linear foot, this can significantly impact project budgets. Additionally, BACnet’s top-down approach to control networks necessitates the use of costly gateways to translate between the protocol used at the workstation level and other protocols used at lower levels.


A distributed control system built to enable communication between intelligent devices, the LonWorks platform employs a flat system architecture to reduce the overall cost to implement, manage and maintain building automation systems. The system comprises the LonTalk communication protocol, a dedicated controller (Neuron Chip) and a network management tool.

Developed in the late 1980s by Echelon Corporation in conjunction with Motorola, LonTalk became an ANSI standard (ANSI/CEA 709.1) in 1999 and an international standard (ISO/IEC 14908-4) in 2005. It is supported by hundreds of manufacturers and, as of 2010, approximately 90 million devices were installed globally with LonWorks technology. Products and applications using this technology include HVAC systems, street lighting, smart meters, train control systems, safety and security systems, and even infant monitoring.


The LonTalk protocol defines a set of rules to manage communications within the control network. Because of the complexity of the LonTalk protocol, Echelon developed its own communications controller (Neuron) optimized for the protocol. The benefit of this approach is that it simplifies system development and frees the rest of the system to focus on applications processing; however, it also restricts system designers to a limited number of Neuron vendors, adding to the cost of system development.

LonTalk is supplemented by a second protocol (LonWorks) that defines the content and structure of the information that is communicated. LonWorks describes a distributed control network operating on a peer-to-peer basis, enabling any device to communicate with any other device on the network and/or employ master-slave communication among intelligent devices. This enables a flat system architecture that is well-suited for modern smart building applications.

The LonWorks platform supports a wide range of physical media, including free-topology twisted-pair, powerlines, fiber optic cable, and coax. The most popular channel in building automation systems is FT-10, which defines a free-topology twisted-pair profile capable of delivering 78kbps over up to 500m of low-cost twisted pair. A powerline channel is also available for low-speed applications (5.4kbps or 3.6kbps, depending on frequency). For high-speed applications, the LonWorks platform uses an affiliated IP tunneling channel with tunneling routers and IP-based LonWorks/IP nodes. This facilitates the integration of new and previously deployed networks with other IP-aware applications and remote network management tools.

Like BACnet, one of the biggest challenges facing the LonWorks protocol in recent years is meeting the performance and cost demands of modern smart building applications. Although the protocol offers many advantages, developers today increasingly struggle to meet the bandwidth demands of new applications with the low bit rates available over twisted-pair and powerline. In practice, this means that powerline has become obsolete in all but the simplest control networks. In its place, system integrators have had to run new wiring and deploy a vast network of costly switches, routers, and repeaters to deliver the throughput demanded by their applications.

LonMark recently addressed these concerns by adopting HD-PLC as a new high-speed communications channel for large, multi-node smart building networks.


Originally developed by Panasonic to meet the bandwidth requirements of multimedia-rich smart home applications, HD-PLC is a broadband technology (2MHz to 28MHz) capable of achieving PHY speeds up to 240Mbps over any wire (powerlines, twisted-pair, and coax).

In 2010, the HD-PLC protocol was ratified in IEEE 1901, the first global standard for powerline communication (PLC) for applications such as multimedia home networking, AV and smart grid. In 2016, HD-PLC was enhanced with a unique multi-hop technology adopted by HD-PLC Alliance and ratified in the international standard ITU-T G.9905. Multi-hop extends the communication range of HD-PLC and adds industrial-grade robustness by enabling each node to act as a repeater so that data can “hop” from one device to another. With multi-hop, one master device can connect to as many as 1024 terminal devices and support communication over distances up to several kilometers.


In addition to its range and robustness advantages, the HD-PLC protocol brings significant performance and cost advantages to smart building networks. System integrators finally have a solution that enables them to meet the bandwidth demands of modern IoT applications using their existing wiring infrastructure: powerlines, twisted-pair and coax.

HD-PLC solves the problems inherent to PLC by applying advanced, broadband communication techniques and utilizing wider bandwidths at higher operating frequencies to achieve a better channel for communication on powerlines. Smart building networks benefit from fast megabit data rates, integrated security, and robust, bidirectional IP-based communications. Meanwhile, system integrators gain the ability to quickly deploy large systems without time-consuming network planning or costly devices like switches and routers, thanks to HD-PLC’s built-in mesh networking functionality.

This is just a brief introduction to the benefits of HD-PLC. Download our whitepaper to learn more about HD-PLC and how it can help you break through bandwidth bottlenecks and cost barriers in your smart building application.

Portrait of Michael Navid

Michael Navid

VP, Marketing and Business Development, MegaChips
Michael is an accomplished business executive who has spent the last 15 years working to advance the communications technologies needed to build a smarter planet. The original founder of the G3-PLC Alliance, he was a key contributor in the evolution of G3-PLC as the premier communications technology for smart grids. Today, Michael is applying his experience and energy to bringing the benefits of HD-PLC to smart cities and smart buildings. When he’s not driving technology transformation, you’ll likely find him in one of his vintage cars heading down Pacific Coast Highway in Southern California.
Connect with him on LinkedIn.