What Is Free Topology? Why It Is Difficult to Implement in Real-World Networks

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Free topology allows flexible wiring without strict endpoint constraints, making it ideal for real-world installations.

Free topology has many benefits:

  • No need to identify or manage cable endpoints, unlike daisy-chain topology
  • Lower installation cost
  • Reduced wiring cost by minimizing total cable length
  • Easy to extend from any point, simplifying layout changes
  • Support for loop connections, enabling redundancy

However, only a few technologies can handle it robustly and at scale.

Why is free topology difficult?

In a free topology network, branches can exist at any point. These branches create impedance mismatches and signal reflections, resulting in frequency-dependent fading (multi-path fading).

A square wave consists of a fundamental frequency and its odd harmonics. When reflections occur, some harmonics are attenuated or canceled, distorting the waveform. This distortion can lead to communication errors.

Which communication technologies can handle this?

Several technologies can handle free topology, with different characteristics:

  • Low-speed RS-485 (~9.6 kbps)
  • Narrowband PLC (~100–500 kbps)
  • Broadband PLC (several Mbps to tens of Mbps)

Low-speed RS-485 can tolerate free topology in practice because its signal spectrum is concentrated at low frequencies, making it less sensitive to reflection-induced notches.

In multi-path environments, shorter branch lengths shift the first notch to higher frequencies. For example, a 500 m branch creates the first notch at around 70 kHz. This is sufficiently higher than the 24 kHz 5th harmonic at 9.6kbps, so low-speed RS-485 is not significantly affected. However, higher data rate signals extend into higher frequencies, where they may overlap with the notch and experience distortion.

 

PLC (Power Line Communication) is inherently suited for free topology networks. The most widely used PLC modulation scheme is OFDM. OFDM divides data across multiple carriers. Even if some carriers are attenuated by notches, communication can continue using the remaining carriers. This makes OFDM highly robust against the frequency-selective fading caused by free topology.

High-Speed Communication in Free Topology: Challenges and Solutions

While low-speed RS-485 works well for simple control signals, its data rate is limited, making it difficult to support modern requirements such as IP-based communication.

Narrowband PLC improves data rates but still has limitations for bandwidth-intensive applications.

Broadband PLC enables significantly higher data rates, making it suitable for modern networks. However, at higher frequencies, not only reflections but also attenuation due to branch splitting becomes significant.

At lower frequencies, 10 branches may behave roughly like 1/10 attenuation.  At higher frequencies, attenuation can increase more rapidly, in some cases approaching exponential behavior (e.g., around 1/2¹⁰ ≈ 1/1024).

To overcome this, multi-hop technology can be used. Multi-hop divides a long, highly attenuated path into multiple shorter links, each with manageable loss. Each node relays the signal, enabling reliable communication over longer distances even under severe attenuation.

Conclusion: Upgrading Free Topology Networks in Real Deployments

Free topology offers significant advantages in real-world installations, especially in buildings, factories, and infrastructure where flexible wiring and future expansion are required.

Broadband PLC combined with multi-hop technology has emerged as a practical candidate to replace legacy low-speed RS-485 networks in such environments. It enables higher data rates while maintaining reliable communication over complex free topology wiring.

One example is Nessum, a Broadband PLC technology that incorporates multi-hop capability. It is already being adopted in real deployments to replace 9.6 kbps RS-485 systems, enabling modern high-speed IP-based communication over existing wiring infrastructure.

 

Get Started Today

Order your Evaluation Kit and experience the benefits of Nessum today!

About the Author

Kengo Tamukai is a senior engineer specializing in wired and wireless communication technologies. With over 20 years of experience in LSI design, system architecture, and technical marketing, his expertise spans SoC design, OFDM-based technologies, and hybrid communication systems, driving innovation in modern digital networks.

 

LonWorks FT-10 Replacement and Migration Guide

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What Comes After the Discontinued Neuron Chip ?

Renesas Electronics has announced the discontinuation of the Neuron® chip.

For many building automation and industrial control systems, this raises a critical question:

How can existing LonWorks FT-10 networks (ISO/IEC 14908-3) be maintained or modernized without rewiring entire buildings?

The answer depends on whether the priority is compatibility or evolution.

Why LonWorks FT-10 Was So Valuable

FT-10 became widely adopted in systems certified by LonMark International because it supported free topology wiring.

Free topology means:

  • Devices can be connected in almost any wiring shape
  • Strict daisy or star topology is not required
  • Installation cost and time are significantly reduced

While many free topology systems operate around 9.6 kbps, FT-10 achieved 78 kbps, offering both higher speed and flexible wiring.

FT-10 is standardized as ISO/IEC 14908-3 within the LonMark protocol family.

Its real value was not only performance — but the freedom it gave system designers and installers when planning new building wiring.

The Core Challenge: Protecting Existing Wiring

When a key component is discontinued, performance improvements may be attractive.

However, in real buildings, rewiring is often the largest cost and risk factor.

Free topology wiring introduces reflections and impedance variations.
Not all communication technologies tolerate this well.

This makes direct replacement more complex than simply choosing a faster PHY.

Is There a Direct FT-10 Compatible Alternative?

Yes.

There are solutions designed to maintain compatibility with existing FT-10 networks, including:

  • Babi-LON
  • FetLON

These solutions implement FT-10 compatible communication, allowing continued operation without changing the physical architecture.

For projects where the primary objective is to maintain the existing LonWorks architecture with minimal change, compatibility-based approaches can be practical.

However, they typically preserve the same bandwidth and overall system structure.

They extend the current design — but do not fundamentally expand it.

Is Ethernet a Replacement Option?

Single Pair Ethernet technologies such as 10BASE-T1L are sometimes considered.

10BASE-T1L supports long cable distances and can operate in daisy-chain configurations.

However, it does not support true free topology wiring.
Structured cabling and controlled topology are still required.

In many existing FT-10 installations, wiring is branched and optimized for flexibility rather than strict topology rules.

As a result, migrating to Ethernet often requires partial or full rewiring — increasing cost and complexity.

Why Power Line Communication Technology Is a Strong Candidate

Power Line Communication (PLC) technologies are inherently tolerant of complex and irregular wiring environments.

Unlike conventional Ethernet, PLC is designed to operate over branching structures where reflections may occur.

There are two major categories:

  • Narrowband PLC (e.g., G3-PLC)
  • Broadband PLC (e.g., Nessum)

G3-PLC is widely used in smart meters and optimized for long-distance, low-bandwidth communication.

Modern control systems — both in buildings and in energy infrastructure — increasingly require higher throughput and faster response.

Broadband PLC technologies such as Nessum provide significantly higher bandwidth while preserving free topology capability.

As a result, Nessum is being adopted not only in building automation systems, but also in next-generation smart meters that demand fast communication for real-time grid control.

Technology Comparison

Feature

FT-10

G3-PLC

Nessum

Topology

Free

Free

Free

Polarity Sensitive

No

No

No

Termination Required

Yes

No

No

Distance Between Two Nodes

300 m

2,000 m

500–1,000 m

Total Cable Length

500 m

2,000 m

2,000 m

Data Rate

78 kbps

~250 kbps

~10,000 kbps

Nessum preserves the installation flexibility of FT-10 while enabling substantially higher performance.

Standardized Evolution Within the Lon Family

FT-10 is standardized as ISO/IEC 14908-3.

Nessum is standardized as ISO/IEC 14908-8.

ISO/IEC 14908 defines the LonMark protocol stack.

Being assigned a dedicated part number within this series means Nessum is officially recognized as a standardized link layer option within the Lon ecosystem.

This is significant.

Nessum is not an external overlay technology.
It is positioned as a formal evolution path within the same ISO/IEC 14908 framework. This provides long-term interoperability assurance and protects system investment.

In addition, Nessum enables:

  • Higher communication speed
  • Larger and more scalable networks
  • Integration with IP-based protocols such as BACnet/IP

With its Ethernet bridge capability, migration toward IP networking can occur step by step — without immediate large-scale rewiring.

Conclusion: Compatibility or Evolution?

The discontinuation of the Neuron chip creates two strategic paths for FT-10 (ISO/IEC 14908-3) systems.

Compatibility Path
FT-10 compatible solutions such as Babi-LON and FetLON allow continuation of the existing architecture with minimal structural change.

Evolution Path
Nessum (ISO/IEC 14908-8) preserves free topology wiring while expanding bandwidth, scalability, and IP readiness. The core requirement of free topology has not changed.

 

The key decision is whether to:

  • Maintain the current system design
  • Or use this transition as an opportunity to modernize while protecting existing wiring

Rather than simply replacing a discontinued chip, organizations can choose a structured, standards-based migration strategy that aligns with long-term building communication needs.

 

Frequently Asked Questions

What replaces LonWorks FT-10 after the Neuron chip discontinuation?

There are two approaches:

  • FT-10 compatible solutions (e.g., Babi-LON, FetLON) for maintaining existing architecture
  • Nessum (ISO/IEC 14908-8) for preserving free topology while enabling higher performance and future IP integration

Can existing LonWorks FT-10 wiring be reused?

Yes.

Both FT-10 compatible solutions and PLC-based technologies such as Nessum are designed to operate over free topology wiring.

Ethernet technologies such as 10BASE-T1L typically require structured topology and may require rewiring.

Is Nessum officially recognized within LonMark?

Yes.

FT-10 is defined as ISO/IEC 14908-3, and Nessum is defined as ISO/IEC 14908-8.
Both belong to the ISO/IEC 14908 series that defines the LonMark protocol stack.

Why not simply migrate to Ethernet?

Ethernet assumes structured topology and controlled cabling conditions.
Many existing free topology installations do not meet these requirements without redesign.

Get Started Today

Order your Evaluation Kit and experience the benefits of Nessum today!

About the Author

Kengo Tamukai is a senior engineer specializing in wired and wireless communication technologies. With over 20 years of experience in LSI design, system architecture, and technical marketing, his expertise spans SoC design, OFDM-based technologies, and hybrid communication systems, driving innovation in modern digital networks.

The Invisible Ethernet Cable – Replacing Short Ethernet Links with Nessum Air

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When people hear “wireless communication,” they usually imagine Wi-Fi or Bluetooth—signals spreading widely through space, sometimes slow, sometimes unstable, and often affected by interference.

Nessum Air takes a fundamentally different approach.
Instead of trying to reach far, it is designed to replace very short Ethernet links—the kind of connections where you would normally use a 100BASE-T cable over tens of centimeters.

By focusing only on communication with the device right next to it, Nessum Air functions as an invisible Ethernet cable, enabling high-speed, reliable, and secure connections, while also allowing many links to be placed densely side by side without interference, all without physical contact.

What Makes Nessum Air Different?

Nessum Air is a short-range wireless technology that behaves much more like a cable than a conventional radio system.

It is designed with a physical layer capable of very high data rates (up to 500 Mbps PHY), allowing two nearby devices to exchange data at high speed without any physical connector. The communication distance is intentionally limited to about 0.5 m and can be adjusted by the size of a small loop antenna.

Unlike Wi-Fi or UWB, which use radiated electromagnetic waves designed to travel far, Nessum Air uses magnetic field coupling.
Magnetic fields decay rapidly with distance and remain tightly confined around the source, which naturally limits how far the signal spreads.

Because of this physical behavior:

  • Signal spread is far smaller than with radiated radio
  • Installation density can be increased by dozens of times
  • Interference between nearby links is minimized
  • Communication remains stable even around metal, dust, oil, or water

In short, Nessum Air trades long-distance reach for precision and stability—exactly what short Ethernet links require.

How Is It Different from Other Wireless Technologies?

Technology Distance Medium Frequency PHY rate
Nessum Air ~0.5m Magnetic field ~56MHz ~500Mbps
NFC ~0.1m Magnetic field 13.56MHz ~0.4Mbps
UWB ~10m Radiated waves 3,100-10,600 MHz ~480Mbps
  • NFC is safe and localized, but far too slow for Ethernet replacement.
  • UWB can be fast, but its radiated signals spread widely, making dense deployment difficult.
  • Nessum Air combines short range with wired-class speed, while keeping signal spread tightly controlled.

What Can You Do with an Invisible Ethernet Cable?

  • A Wear-Free Ethernet Link for Rotating Machines

Rotating machines often rely on slip rings to carry Ethernet or control signals across rotating interfaces. These mechanical contacts wear out, generate noise, and require maintenance.

With Nessum Air, a stationary unit and a rotating unit can exchange Ethernet-class data without touching at all.

There is no mechanical wear, no contact noise, and no connector maintenance—yet control signals and even video data can flow continuously.
In environments exposed to oil, dust, or vibration, Nessum Air provides a practical alternative to conventional slip rings.

  • “Wireless 100BASE-T” Service and Maintenance Connections

In many devices, Ethernet connectors are needed only for setup, diagnostics, or maintenance—but exposing a physical port reduces reliability and sealing.

Nessum Air can act as a temporary, proximity-based Ethernet cable.

By bringing a Nessum Air interface close to a device—much like attaching a magnetic connector—you can access an internal Ethernet port without opening the enclosure.

This is ideal for:

  • Maintenance or service ports not intended for end users
  • Fully sealed or waterproof equipment
  • Systems where exposed connectors are a reliability risk

When you remove it, the Ethernet connection disappears.

 

  • Modular Systems Without Ethernet Wiring

Nessum Air’s short range and limited signal spread naturally enable modular system design.

Each device behaves as a self-contained module with a short-range Ethernet interface.

When modules are placed side by side, Ethernet traffic passes from one module to the next—without cables, connectors, or manual configuration.

Typical examples include:

  • High-density server racks
  • Automated warehouse storage systems
  • Gaming machines installed in rows
  • Expandable delivery lockers
  • Digital signage and video walls

In these systems, adding or removing modules simply extends or shortens the Ethernet chain, while maintaining high-speed, secure, and interference-free communication.

Conclusion

Nessum Air is not meant to replace Wi-Fi, cellular networks, or long Ethernet cables.

Its purpose is more specific:
to replace short Ethernet links in places where cables cause wear, complexity, or reliability problems.

By combining a high-speed physical layer with tightly confined magnetic-field communication, Nessum Air functions as an invisible Ethernet cable—enabling higher installation density, improved reliability, and simpler system design.

As systems become more compact, sealed, and modular, Nessum Air offers a clear and consistent approach to connectivity:
not by reaching farther, but by replacing short cables more precisely.

Get Started Today

Order your Evaluation Kit and experience the benefits of Nessum today!

About the Author
Kengo Tamukai is a senior engineer specializing in wired and wireless communication technologies. With over 20 years of experience in LSI design, system architecture, and technical marketing, his expertise spans SoC design, OFDM-based technologies, and hybrid communication systems, driving innovation in modern digital networks.

Smooth Migration from Serial to IP: A Future-Proof Solution with Nessum

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Many devices in existing buildings and facilities still rely on legacy serial communication protocols such as Modbus RTU. At the same time, newly added equipment—including BMS controllers, sensors, AI cameras, and IoT gateways—are typically IP-based. While serial communication wiring is often already installed (frequently routed through conduits or embedded in walls), rewiring for Ethernet is difficult and costly. Furthermore, serial communication has limitations in terms of scalability and transmission speed.

Nessum’s Ethernet and serial bridging functionality offers an effective solution to these challenges, enabling a seamless transition to IP-based networks without abandoning the existing serial infrastructure.

Limitations of Traditional Ethernet Extenders

One conventional solution is the Ethernet extender, which transmits high-frequency signals over existing wiring without interfering with ongoing serial communication. However, most Ethernet extenders only support point-to-point connections. This makes them suitable for connecting a single IP device, but not ideal for integrating multiple IP devices over a shared serial cable.

Nessum’s Unique Approach

Nessum’s core functionality is Ethernet bridging. The entire Nessum network operates like a Layer 2 (L2) switch, where each Nessum device functions as a port of the switch. When an Ethernet device is connected to a Nessum node, Ethernet packets are automatically bridged across the network—without any configuration—just like a plug-and-play L2 switch.

 

In addition to Ethernet bridging, Nessum also supports serial bridging. Data received on the serial port is encapsulated into Ethernet packets and routed to the appropriate destination address, using the same mechanism as Ethernet bridging. This dual-bridging capability allows serial and IP devices to operate simultaneously over the same physical cable.

 

From a topology standpoint, Nessum’s multi-hop capability and OFDM-based modulation enable communication over existing serial communication cables—even in free topology. While high-frequency communication (in the MHz range) typically faces challenges like signal reflections and attenuation at cable branches, Nessum is specifically designed to overcome these issues. This makes it highly suitable for retrofitting and expanding networks without the need for new wiring.

 

By simply attaching Nessum devices to existing serial endpoints, new IP devices can be added alongside legacy serial devices with no service interruption. While there is an initial cost to install Nessum devices, the result is a hybrid architecture that supports gradual, step-by-step migration from serial to IP communication.

 

To enhance security, Nessum also applies AES-128 encryption to all communications. This significantly improves the protection of serial communication lines, which are typically unencrypted and vulnerable to interception or tampering.

 

 

 

Conclusion

Nessum offers a practical and future-ready solution for bridging legacy serial systems with modern IP networks. Its plug-and-play Ethernet and serial bridging, flexible topology support, and built-in encryption make it ideal for facilities seeking to modernize without the disruption and cost of rewiring. Whether you’re planning a gradual upgrade or preparing for large-scale digital transformation, Nessum provides a reliable and secure migration path from serial to IP.

 

Get Started Today

Order your Evaluation Kit and experience the benefits of Nessum today!

 

About the Author
Kengo Tamukai is a senior engineer specializing in wired and wireless communication technologies. With over 20 years of experience in LSI design, system architecture, and technical marketing, his expertise spans SoC design, OFDM-based technologies, and hybrid communication systems, driving innovation in modern digital networks.

Nessum Basics FAQ: What It Does and Why It’s Unique

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If you’ve never heard of Nessum, you’re not alone.
Even though the technology behind it has been around since the early 2000s under the name HD-PLC, it’s still relatively unknown outside of specific industries.
So, the first reaction many people have is:
“Nessum? What’s that supposed to be?”

Here’s the simple answer:
   Nessum is like a networking bridge that lets your devices talk to each other — whether they use Ethernet or old-fashioned serial connections — all over the wires you already have.

Instead of pulling new cables or replacing old equipment, Nessum makes it possible to:

  • Plug in Ethernet devices and connect them instantly
  • Keep using legacy serial devices like sensors or controllers
  • Extend networks across power lines, twisted pairs, or almost any existing wiring

And while the roots of Nessum come from HD-PLC, it has continued to evolve with industrial use in mind — adding flexibility, reliability, and scalability that make it practical for today’s building and factory networks.

In this FAQ, we’ll cover the most common questions to give you a clear picture of what Nessum does and why it matters.

 

Q1. How is a Nessum network structured?

A Nessum network consists of one Master device and multiple Terminal devices.

Think of the Master as the main point that organizes the network, but devices can also communicate directly with each other. This simple structure allows all connected devices to exchange information reliably over the same wiring, whether it’s twisted pair or other types of existing cables.

Q2. What is the basic function of Nessum?

Nessum works like a plug-and-play bridge.

  • For Ethernet devices: just plug them in, and packets flow as if through a standard Layer 2 (L2) switch.

  • For serial devices: data is encapsulated into Ethernet packets and sent across the network.

Nessum supports Modbus RTU and Modbus ASCII by default, and can also bridge other serial protocols if destination address information is defined.

This dual bridging allows Nessum to connect both modern Ethernet devices and legacy serial equipment seamlessly.

Q3. Is Nessum just another L2 switch?

Not exactly.
While Nessum behaves like an L2 switch from the outside, it isn’t competing with network switches. The big difference is the medium:

  • Nessum can operate over existing power lines, twisted pairs, or almost any wire, and even short-range wireless.

At the same time, Nessum provides many of the same functions as an L2 switch, including:

  • VLAN support for flexible network segmentation
  • MAC address filtering for traffic control and security
  • PTPv2 support for precise time synchronization across devices

This makes it much more than just a simple bridge.

Q4. Is the communication secure?

Yes.
The Master device handles authentication and encryption key distribution. Communication uses AES-128 encryption, with keys dynamically updated to maintain strong security.
This ensures reliability even in industrial or building environments.

Q5. Can multiple Nessum networks be connected together?

Yes.

  • You can directly link multiple Nessum networks using Ethernet cables or through another L2 switch.
  • From the outside, the whole system still behaves just like a standard L2 switch.

This makes expansion straightforward.

Q6. What is Multi-hop, and why does it matter?

Multi-hop allows packets to automatically route across multiple Nessum devices within the same network.

  • Each hop extends the effective communication range.
  • From the outside, it still looks like a simple L2 switch — no extra setup required.

This feature is particularly important for replacing long-distance serial communication. With Multi-hop, Nessum can cover distances far beyond a single Ethernet or serial link, making legacy serial networks realistic to upgrade.

Conclusion

Nessum is not just another switch. It is a unifying bridge that:

  • Extends IP networking over existing wiring
  • Connects both Ethernet and serial devices (with Modbus RTU/ASCII support)
  • Provides key L2 switch features like VLAN, MAC filtering, and PTPv2
  • Ensures secure communication with AES-128 encryption
  • Scales across long distances with Multi-hop

By combining these capabilities, Nessum makes the transition from legacy systems to modern IP networks both practical and cost-effective.

 

Get Started Today

Order your Evaluation Kit and experience the benefits of Nessum today!

 

About the Author
Kengo Tamukai is a senior engineer specializing in wired and wireless communication technologies. With over 20 years of experience in LSI design, system architecture, and technical marketing, his expertise spans SoC design, OFDM-based technologies, and hybrid communication systems, driving innovation in modern digital networks.