Converged Networks: One IP Backbone for All Building Systems in Ireland

Not long ago, every building system in Ireland ran on its own dedicated cabling infrastructure. CCTV had its own coaxial or Cat5 network, access control ran on RS-485 loops, fire alarm used its own STP cable, DALI lighting had its own 2-wire bus, the BMS communicated over BACnet MSTP, and the ICT team managed an entirely separate structured cabling plant. The result was a building with six, eight, or even ten parallel networks — expensive to install, complicated to manage, and impossible to integrate meaningfully at a data level.

The converged building network changes all of this. By carrying every building system payload — security, life-safety signalling, lighting control, HVAC automation, AV, ICT and IoT — over a single physical IP infrastructure, a converged network slashes capital expenditure, simplifies ongoing management and, crucially, enables the cross-system analytics that define a genuinely smart building. This guide explains how converged networks are designed for Irish projects, what VLAN architecture is required, how QoS is applied, and what designers must get right to remain compliant with NIS2 and Irish building regulations.

The Old Model: Separate Networks for Every System

The traditional approach to building networks was driven by the organisational silos of the design team. The mechanical engineer specified BMS cabling, the ELV consultant specified security and fire cabling, the ICT consultant specified structured cabling, and the lighting consultant specified DALI wiring. Each discipline worked to its own standards and its own installer base. The result, from a building infrastructure perspective, was massively redundant.

A typical 10,000 m² Irish office building built before 2015 might have had: a 24-core fibre backbone for ICT, a separate 12-core fibre for CCTV, RS-485 wiring loops for access control, dedicated STP for BMS field devices, analogue cable for DALI zones, and additional cabling for AV. Each system had its own comms room or IDF, its own power feeds, its own UPS provision and its own maintenance contract. The total installed cost of this parallel infrastructure, relative to a converged network delivering the same functions, was typically 35 to 45% higher.

The Converged Model: One Physical Layer, Many Logical Networks

The converged network collapses all of this into a single physical IP infrastructure — typically comprising a fibre optic backbone between main distribution frames and individual floors, with Cat 6A horizontal cabling to endpoints, all managed through a hierarchy of access, distribution and core switches. The physical layer is shared; the logical separation between systems is achieved through VLANs, QoS marking and OT/IT firewall policies.

The key technologies enabling convergence are: Power over Ethernet (PoE) for devices that previously needed separate power supplies, IP-native versions of previously proprietary protocols (BACnet/IP, DALI-over-IP, ONVIF for CCTV), and 1GbE and 10GbE switching infrastructure that provides ample bandwidth for simultaneous payloads from all building systems.

VLAN Architecture for Converged Irish Buildings

VLAN segmentation is the cornerstone of a well-designed converged network. Without it, a converged network is merely a flat network — one where a compromised IP camera could communicate directly with a BMS controller. Proper VLAN design creates logical isolation between systems while maintaining the ability to pass controlled data between VLANs through inter-VLAN routing with firewall inspection.

VLAN Naming Convention

Irish projects benefit from a consistent VLAN naming convention that can be handed over to the building management team and maintained consistently across campus buildings or multi-tenanted developments. A recommended convention is: VLAN 1 Management, VLAN 10 ICT, VLAN 20 CCTV, VLAN 30 ACS, VLAN 40 Voice, VLAN 50 Wi-Fi, VLAN 55 Guest, VLAN 60 BMS-OT, VLAN 70 AV, VLAN 80 IoT-EV. The Guest VLAN must be completely isolated from all OT VLANs with no inter-VLAN routing path and restricted to internet-only access through a captive portal.

QoS Design and DSCP Marking

Quality of Service (QoS) is what makes convergence viable for latency-sensitive and time-critical systems. Without QoS, a burst of CCTV video traffic during a building incident could degrade VoIP call quality or delay BACnet polling cycles. With a properly engineered QoS policy, each traffic class receives the forwarding priority appropriate to its function.

VoIP receives Expedited Forwarding (EF, DSCP 46) — the highest queue priority with guaranteed bandwidth and strict scheduling. Video streams receive Assured Forwarding class 4 (AF41, DSCP 34). BMS and OT traffic receives CS2 marking. Best-effort ICT data and IoT telemetry receive CS0. The switch configuration must trust DSCP markings from managed building system devices and apply the appropriate egress queuing policy on every port and uplink. For Irish healthcare projects, nurse call and clinical alarm traffic should receive VoIP-class EF marking to ensure sub-100ms delivery.

PoE Budget Planning and Aggregation

Power over Ethernet is one of the most compelling aspects of network convergence — eliminating the need for local power supplies at cameras, access readers, Wi-Fi APs, IoT sensors, VoIP handsets and DALI gateways. However, PoE budget aggregation requires careful engineering. A worked example for an Irish office floor plate: 8 CCTV cameras at 15W = 120W, 4 Wi-Fi 6 APs at 25W = 100W, 20 IP desk phones at 6W = 120W, 6 access control readers at 10W = 60W, 12 IoT sensors at 4W = 48W, 2 DALI gateways at 12W = 24W. Total PoE draw: 472W against a 48-port PoE+ switch's typical 740W budget — 64% utilisation. Designers should aim for no more than 70 to 75% of rated PoE budget in normal operation to allow for future devices and worst-case cold-start inrush.

NIS2 OT/IT Firewall Requirements

The EU's NIS2 Directive, transposed into Irish law, has direct implications for converged building networks in critical infrastructure sectors including healthcare, energy, transport and public administration. NIS2 requires that OT networks are protected by security controls including network segmentation, access control, audit logging and incident response capability. For converged buildings, this means the BMS-OT VLAN must be protected by a dedicated OT/IT firewall — not merely a switch ACL. Products from Fortinet, Cisco (ISA3000), Claroty or Nozomi Networks provide OT-aware deep packet inspection that understands BACnet, Modbus and other building protocol traffic.

The firewall must log all inter-VLAN sessions, block unsolicited connections from IT to OT VLANs, and generate alerts for anomalous protocol behaviour such as unexpected BACnet write commands. This requirement is not optional for publicly funded Irish buildings in NIS2 scope. ASDV recommends incorporating the OT/IT firewall specification into ELV tender documentation at RIAI Stage 3, with commissioning validation of rule sets prior to practical completion.

Cost Savings: The Business Case for Convergence

The financial case for converged networks in Irish projects is compelling. Analysis of Irish commercial projects completed between 2022 and 2025 demonstrates consistent savings in the range of 25 to 40% on overall network infrastructure cost compared to equivalent parallel network designs. The main saving vectors include: elimination of duplicate fibre backbone risers (saving €15,000 to €40,000 per building depending on height and footprint), consolidation of IDF rooms (reducing from 8 to 12 separate comms rooms to 4 to 6), reduced electrical distribution requirements for separate system power supplies, a single network management platform replacing multiple system-specific tools, and reduced contractor coordination overhead during installation and commissioning.

Ongoing operational savings are also significant: a single network operations team can manage all building systems through a unified NMS (Network Management System), whereas a fragmented parallel network approach requires coordination between multiple specialist contractors for routine moves, adds and changes. For a typical 10,000 m² Dublin office, the CAPEX saving on network infrastructure alone is in the range of €80,000 to €150,000.

IEEE 802.1Qbv and Time-Sensitive Networking

Looking forward, Time-Sensitive Networking (TSN) — specifically IEEE 802.1Qbv, which defines scheduled traffic shaping — is beginning to appear in advanced building automation specifications. TSN provides deterministic, guaranteed latency for time-critical control traffic alongside best-effort data on the same physical network. In Irish smart buildings, TSN is most relevant for industrial-grade HVAC control loops, precision lighting control for broadcast or healthcare environments, and building-to-grid energy management where sub-millisecond synchronisation with grid signals is required. TSN-capable switches are available from Cisco, Siemens and others, though mainstream Irish commercial project deployment remains at the early-adopter stage in 2026 with wider adoption expected from 2027 as costs normalise.

Design Considerations for Irish Designers

BCAR (Building Control Amendment Regulations) inspection processes in Ireland require that life-safety systems — fire alarm, emergency lighting, access control serving means-of-escape routes — are clearly documented as meeting relevant Irish Standards (I.S. 3218, I.S. 3217) regardless of the physical network infrastructure they traverse. Designers must produce clear evidence that convergence does not compromise the performance or resilience requirements of these systems.

Network resilience is a key design parameter. The converged backbone should employ redundant fibre paths between MDF and IDFs using rapid spanning tree (RSTP) or link aggregation (LACP). For life-safety systems, the switching infrastructure carrying fire alarm signalling should be on UPS-backed power with a minimum 3-hour battery standby — matching the equivalent requirement for dedicated fire alarm cabling infrastructure. These UPS requirements must be coordinated with the electrical services engineer at RIAI Stage 3.