Network for mid-sized to large BACnet MS/TP project structured with centralized primary plants - Basic Documentation - DXR2.E09-101A - PXA.24M - PXC4.E16 - PXC4.E16S - PXC4.M16 - PXC4.M16S - PXC5.E003 - PXC5.E24 - PXC5.E24M - PXC5.E24S - PXC5.E40 - PXC5.E40M - PXC5.E40S - PXC7.E400L - PXC7.E400M - PXC7.E400S

Example for planning and implementing a project.

Demand

• New office building with room automation for 424 rooms over 4 floors as well as preparing the appropriate primary plants.
• Each floor is leased by another tenant and has its own occupancy and use, i.e. the room operating mode as well as associated room setpoints, lighting per floor with central operation, and emergency function.
• Blinds control for each facade including protection, service, and emergency function.
• Central weather station, demand-controlled control of primary plants.
• Schedulers together with a calendar for room operating modes and lighting for each floor, superposed functions on a monitoring device.
• Primary plants for air handling, heat generation and distribution as well as central distribution of refrigeration in an equipment room.
• Primary plants and general: 5 PXC4.E16-2/PXC7 and 5 PXC5.E003
• Desigo room automation: 406 DXR2…
• Visualization, operating and monitoring Desigo CC
• Monitoring network components via SNMP

Planning and implementation, IP network

Core level

Core Switch (Managed Layer 3) as the network core, interface for remote maintenance, and office network as well as building additional IP segments or as a redundant backbone.

Distribution level

Managed layer 2 switches are planned on the distribution level, in the riser zones, i.e. floor distributors that:

• Are connected with copper cabling.
• Ensure that Desigo room automation stations from the given floor are located on its own VLAN and therefore isolated from other Desigo room automation stations on other floors for the purposes of local BACnet broadcasts.
• You can configure port mirroring of each VLAN for network diagnostics and troubleshooting.

Edge level

Only unmanaged layer 2 switches are planned as edge switches. BACnet MS/TP networks can have a max. cable length depending on the set baud rate. If the overall length is, however, exceeded, a new BACnet network must be created and connected via a BACnet MS/TP IP router to BACnet/IP over the Ethernet.

The rules apply again for BACnet/IP networks, i.e. the Ethernet network must be installed as an unmanaged layer 2 switch. A PXC.. can integrated in the given zones to control primary plants, depending on building planning.

IP/VLAN overview

An IP segment can also be divided on a project-by-project bases into a part with static addresses, e.g. automation stations, etc., and a dynamic part (DHCP), e.g. for engineering laptops.

As an alternative, you can also work in general with DHCP. You must ensure, however, that the stations always have the same IP address. This applies to:

• BACnet device that assume BBMD functionality.
• Room automation stations with an on-board web server are operated with the web interface for servicing and diagnostics.

See Web Interface User Guide (A6V11938631).

Planning and implementation, BACnet network

Each Desigo PXC.. automation station should have FDT functionality for maintenance and diagnostics and remote access.

A BACnet internetwork is built using a multiple BACnet networks. The IP segment as well as each MS/TP segment forms a BACnet network. A BBMD must be used in each IP segment in order for BACnet and IP networks to interact. This permits isolating local broadcasts from the flexible room management (room/room segment). Global broadcasts, originating from central functions, are managed on the BACnet device that assumes the BBMD functionality by asymmetrical BDT entries (Broadcast Distribution Table).

Set up the device accordingly in the XWP network configurator. The following table provide an overview of the BACnet configuration:

How and why asymmetrical BDT entries?

Local broadcasts that use the flexible room management to locate and address room segments from the room, are routed to an own VLAN or BACnet network to a defined UDP port (0xBAC0). Local broadcasts are thus encapsulated and no longer forwarded to other networks.

BACnet Broadcast Management Devices (through the BDT) must, however, be defined for global BACnet broadcasts (originating, among others, from central functions) to operate successfully on the different IP segments and BACnet networks.

From the project topology above, a PXC5.E003 (BNR501) must be in the building scope for performance reasons:

• Support the BBMD function on the first port.
• Enter its own IP address in the BDT to 0xBAC0 (1.Port).
• Enter all other IP address for the BBMDs in the other IP segments that also communicated on UDP port 0xBAC0.

A BBMD must be defined for any other IP segments, i.e. the BDT is also enabled on the PXC5.E003 to BAC0. In the BDT is the own IP address and address for BNR501.

The Desigo CC management platform registers as a third-party device in BNR501. The broadcast can be triggered here and forward via the asymmetrical BBMD entries to all other participants in the various IP segments.

As an alternative, you can of course work with DHCP. Important is that all devices that support BBMD functionality must receive a fixed IP address.

Planning and implementation, HVAC and room automation

Plant scope:

• Desigo PXC4/7 to control primary plants.

Building scope:

• Desigo PXC5.E003 and DXR2.E18 for superposed functions, e.g. scheduler for occupancy and use times by floor and central functions across floors.
• PXC5.E003 as central BBMD for structuring the BACnet networks.

Floor scope:

• Desigo DXR2.E18 exclusively for central functions.
• Desigo DXR2.M.. for rooms with HVAC, lighting, and blinds, or room segments with HVAC.
• PXC5.E003.

You can operate with cascading group manager functions if lighting and blinds exceed a maximum of 500 commandable group members. This can, for example, be used for emergency control of blinds actuators over multiple facades over lighting over multiple floors.

Planning and implementation of central functions

Recommendation: Network components

• Siemens SCALANCE XB005 - as the edge switch for cabling PXC and Desigo room automation stations.
• Siemens SCALANCE XB205 - At the distribution level in the riser zones for setting up VLANs and port mirroring for diagnostics.
• Siemens SCALANCE XM405 - As core switch for possible IP routing.

Siemens SCALANCE switches from the product family X-200 or X-400 support SNMP and can be monitored on Desigo CC.

IT security and IT basic protection

The elements of infrastructure, IT systems, networks, and applications must be discussed under the aspects of security and appropriate measures need to be developed. Customer, domestic, or industry guidelines and directives must be observed under all circumstances.

For additional details, see Desigo Cybersecurity Guidelines Application Guide (A6V14142297) and Practical Guide on IP Networks in Building Automation and Control Systems (CM110668).

Reliability and redundancy

Distribution switches can be cabled on the floor distributors from the core switch in a Gbit ring as backbone if the customer requires extended availability. To this end, special network components must be planned on midsized to highly complex networks with basic cabling of fiber optics and copper cable.

Yet another level for increasing reliability and redundancy is to employ two core switches at different locations.

Cabling the distribution switches

The distribution switches can be cabled in RSTP, increasing reliability. The BACnet MS/TP IP routers are either connected directly to the distribution switch or on remote edge switches.

Benefits

• The backbone is connected redundantly as ring.
• The smaller, e.g. unmanaged switches are connected in a star topology based on importance or price pressure.
• Cost savings during installation.
• Compromises are possible, e.g. more important devices can be planned directly on the ring switch.

Disadvantages

• Distribution switches typically support SNMP; a failure can be reported via the Desigo CC management platform. This would go unnoticed in this topology.
• The probability of failure increases for switches connected in a star topology.

For details, see Section 3.3.5 in Practical guide on IP networks in building automation and control (CM110668).

Summary

The following tables show how to depict all devices and network components in a midsized to large project.