A converged network carries building systems such as automation, video surveillance, access control and lighting controls over the same cabling and switches as the corporate network, separated logically rather than physically. Done well, it saves cable, switches and rack space and gives one place to monitor everything. Done carelessly, it lets a problem in one system reach all the others, so segmentation, ownership and change control matter as much as the hardware.
How building systems ended up on IP
Building systems used to run on their own wiring. Each contractor brought a dedicated network: the controls contractor ran serial buses between controllers, the security contractor ran coaxial cable to cameras, and the access control panels had their own wiring back to a server in a closet. Each system had its own switches, if any, and its own way of doing things.
Over time, most of these systems moved to Ethernet and IP. Building automation controllers speak BACnet/IP or Modbus TCP, cameras are IP devices powered over Ethernet, door controllers report to a server over the network, and lighting controls, meters and elevator monitoring often do the same. Once everything speaks IP, the question becomes whether each system keeps its own switches and cable or shares one well-designed network.
Benefits and risks
The case for convergence is practical. One structured cabling plant serves everything, so there are fewer cables in ceilings and fewer switches to power, cool and maintain. Redundancy, backup power and monitoring built for the core network benefit every system on it. Data from different systems, such as occupancy from access control and space temperatures from the BAS, becomes easier to bring together.
The risks are just as real:
- Shared failure. A switch failure or a misconfiguration can now affect several systems at once.
- Wider attack surface. Building controllers were often designed for closed networks and may have weak authentication. On a shared network without segmentation, they are reachable from places they never should be.
- Blurred responsibility. When the camera system stops recording, is it the network, the recorder or the camera? Without clear ownership, every problem becomes a three-way argument.
- Change control. An IT firmware update or a switch replacement can break a building system that nobody in IT knew depended on it.
How the layers fit together
Most building automation still has a field level that is not IP at all. Sensors and valves connect to controllers by wired inputs and outputs, and smaller controllers, drives and meters often sit on serial buses such as BACnet MS/TP or Modbus RTU. Plant controllers and gateways connect those buses to the IP network, where the supervisory server and operator workstations live.
This layering is useful. The field level keeps running if the IP network has a problem, because controllers carry on with their programmed sequences. What is lost is supervision, trending, alarms to operators and changes from the workstation. Our guide to building automation systems explains the controller side in more detail.
What should not converge
Some systems stay on their own circuits whatever else shares the network. The fire alarm system is the clearest example. It is installed to CAN/ULC-S524, uses control units listed to CAN/ULC-S527 and relies on supervised circuits that the data network cannot replace. Interlocks such as fan shutdown, door release and elevator recall are wired as the fire alarm design and code require. A building network may receive fire alarm status for display or logging through an interface intended for that purpose, but it does not carry the alarm signalling itself.
Check the current editions of the standards and the building code adopted in your province, and involve the fire alarm designer before connecting anything to the fire alarm system. Our guide to fire alarm interfaces covers how those connections are normally made.
Design rules that make convergence work
- Each system has its own VLAN and subnet, with a written firewall policy between segments.
- Each system has a named owner, and the network team knows which switch ports and VLANs belong to it.
- Switches serving security and building systems have backup power sized for those systems, including PoE loads.
- Remote access for contractors goes through one controlled path with individual accounts and logging.
- Network changes affecting building systems go through change control that includes facilities.
- Time synchronization is consistent across systems, so logs and video can be lined up after an incident.
- Default passwords on controllers, cameras and panels are changed and recorded securely.
A typical scenario
A school board is renovating an older school. The existing BAS runs on its own small switches in mechanical rooms, the cameras run on a separate network installed by the security contractor, and the card access system has its own server. The renovation adds new cabling throughout.
In a converged design, the new cabling serves all four systems from the same IDFs. Each system gets a VLAN, the firewall policy lets each system reach only its own server, and the controls and security contractors each get a remote access account limited to their segment. The IT team manages the switches; the facilities team owns the BAS and security servers; and both sign off on changes that touch the other's systems. The fire alarm system is replaced under its own design, with a read-only status interface to the BAS for alarm display.
Questions to ask before you converge
Whether you are planning a new building or bringing existing systems onto a shared network, these questions bring out the decisions that are otherwise made by accident:
- What does each system need from the network? Bandwidth for video, PoE for cameras and readers, low delay for intercoms, and how long each can tolerate an outage.
- What does each system do when the network is down? Door controllers may work offline; cameras may record locally or not at all; the BAS keeps running but stops reporting alarms.
- Who supports each system, and how do they connect? List the contractors, their remote access needs and their contract terms for response.
- What do the system vendors require? Some manufacturers set conditions for network configuration, multicast, or supported switch features. Find out before equipment is chosen.
- Who approves changes? Agree on a change process that covers both IT and facilities before the first outage, not after.
- How will you know something has stopped? Network monitoring should alert when a camera, controller or door panel drops off, not just when a switch fails.
How ehZee can help
Our network design service plans converged networks with segmentation, ownership and change control written into the design, and our building automation design work covers the controller side. For the security side of segmentation, see VLANs and network segmentation.
Common questions
Will IT and facilities both have access to the switches?
Usually IT manages the switches and facilities owns the building systems that use them. The design should state who can change what, and how each side is told about changes that affect the other.
Can our controls contractor still work remotely?
Yes, through a controlled remote access path that reaches only the BAS segment, with individual accounts rather than a shared login. That is safer than the modems and port forwards often found in older buildings.
Is convergence always cheaper?
Usually on cabling and switches, but the savings depend on the design and on someone owning the shared network. A converged network nobody manages can cost more in downtime than separate systems would have.