BACnet Network Types: Choosing Between MS/TP, IP, and Ethernet

Imagine a bustling city with three transportation systems: a slow but reliable bus network, a flexible car system that uses existing roads, and a fast train that runs on dedicated tracks. Each serves a different purpose—buses for frequent stops, cars for door-to-door flexibility, trains for high-speed, long-distance travel. BACnet networks work the same way. They come in three primary types, each with its own strengths and ideal use cases.

In this article, we’ll explore BACnet’s network options using the city transportation analogy, create a clear comparison table, and explain the critical role of BACnet Broadcast Management Devices (BBMDs) in IP networks.

The City Transportation Analogy

Let’s map BACnet network types to city transportation systems:

| BACnet Network Type | Transportation Analogy | Key Characteristic |

|————————-|—————————-|————————-|

| MS/TP | City Bus System | Slow but reliable, good for frequent stops |

| BACnet/IP | Private Car System | Flexible, uses existing roads, fast for point-to-point travel |

| BACnet Ethernet | Train System | Fast, runs on dedicated tracks, less flexible |

Now, let’s dive into each network type in detail, using this analogy to explain their features, benefits, and best uses.

1. MS/TP: The City Bus System

MS/TP (Master-Slave/Token-Passing) is BACnet’s “bus network”—slow, reliable, and designed for devices that don’t need high-speed communication.

How It Works

Only the device with the token can talk (like only one bus at a stop at a time)

Transportation Analogy: City Bus Routes

Fixed Routes: Devices must be connected in a line (daisy chain)

Key Technical Details

Cable Length: Up to 1,200 meters (3,937 feet) with 9.6 kbps, less at higher speeds

Ideal Use Cases

Cost-sensitive installations

2. BACnet/IP: The Private Car System

BACnet/IP is BACnet’s “car network”—flexible, fast, and designed to use existing IP infrastructure.

How It Works

Can be routed between networks using standard IP routers

Transportation Analogy: Private Cars on City Roads

Scalable: Easy to add more cars (devices) as needed

Key Technical Details

Range: Global (can span buildings, campuses, or even the internet)

Ideal Use Cases

Buildings with existing IP infrastructure

3. BACnet Ethernet: The Train System

BACnet Ethernet is BACnet’s “train network”—fast, dedicated, and designed for high-performance applications. It’s less common today, having been mostly replaced by BACnet/IP.

How It Works

Has its own addressing scheme separate from IP

Transportation Analogy: Trains on Dedicated Tracks

Less Flexible: Hard to change routes or add stops

Key Technical Details

Range: Limited to local network segments

Ideal Use Cases

Systems that need guaranteed bandwidth

Comparison Table: Choosing the Right BACnet Network

|————-|———–|—————|———————|

BBMDs: The Traffic Management Centers of BACnet/IP

Now that we understand the main BACnet network types, let’s explore a critical component of BACnet/IP networks: BACnet Broadcast Management Devices (BBMDs).

What Are BBMDs?

In IP networks, routers don’t forward broadcast messages—they’re like roads with no traffic signals for broadcast traffic. BBMDs solve this problem by acting as “traffic management centers” that route BACnet broadcasts between IP subnets.

Why BBMDs Are Needed

They ensure all BACnet devices can find each other across a large IP network

How BBMDs Work: The Traffic Management Analogy

1. Local Broadcast: A device sends a broadcast message (like a car radio announcement)

2. BBMD Receives: The local BBMD catches the broadcast (like a traffic center monitoring radio)

3. Forwarding: The BBMD forwards the message to other BBMDs in the network (like traffic centers communicating via dedicated lines)

4. Delivery: Remote BBMDs broadcast the message locally (like traffic centers rebroadcasting announcements)

Key BBMD Features

Heartbeat Messages: Verify BBMD availability

BBMD Configuration Example

“`

[Building A] ←IP→ [BBMD A] ←IP→ [Router] ←IP→ [BBMD B] ←IP→ [Building B]

“`

This allows devices across buildings to discover each other

How to Choose the Right BACnet Network

Choosing the right BACnet network type depends on your building’s size, budget, and requirements:

Small Buildings (10-50 devices)

Example: Small office building, retail store, school classroom

Medium Buildings (50-200 devices)

Example: Medium office building, hospital wing, hotel

Large Buildings/Campuses (200+ devices)

Example: University campus, large hospital, corporate headquarters

Legacy Systems

Example: Building with existing BACnet Ethernet systems

Future Trends in BACnet Networking

BACnet networking continues to evolve to meet modern building needs:

1. BACnet Secure Connect: Adding encryption and authentication to BACnet/IP for improved security

2. BACnet over Wi-Fi 6/7: Leveraging faster wireless networks for mobile and hard-to-wire devices

3. BACnet over 5G: Enabling remote monitoring and control over cellular networks

4. Integration with Cloud Platforms: BACnet/IP connecting directly to AWS IoT, Azure IoT, and Google Cloud

5. Edge Computing: BACnet devices with built-in edge processing to reduce network traffic

Conclusion: The Right Network for Your Building

Just like choosing the right transportation for your city trip depends on distance, speed, and cost, choosing the right BACnet network depends on your building’s size, budget, and requirements. MS/TP is like a reliable city bus for small systems, BACnet/IP is like a flexible car for large, modern buildings, and BACnet Ethernet is like a fast train for legacy systems.

BBMDs act as traffic management centers, ensuring BACnet/IP broadcasts reach their destination across large networks. With the right network design and BBMD configuration, you can create a BACnet system that’s efficient, reliable, and scalable for your building’s needs.

So, the next time you’re planning a BACnet installation, think about your building as a city, and choose the transportation system (network type) that best serves its needs. Whether it’s buses, cars, or trains, the right BACnet network will keep your building running smoothly for years to come.