Example network - Metasys - LIT-12013055 - Gateway/Router - Cisco Switch - 12.0

Cisco IE 2000 and IE 4010 Ethernet Switches for Metasys Networks Installation Instructions and Troubleshooting Guide

Product name
Cisco Switch
Document type
Troubleshooting Guide
Document number
Revision date

The following figure shows an example network in a building automation system.

Figure 1. Example IP network with Cisco switch

In this example, the physical wiring alone does not provide enough information to fully understand the network. The network engine supervises the controllers connected to the switch, to the CVE in the mechanical room, and to the CVEs and CGEs in the office area. The ADX is connected on the IT side of the network.

In a network of unmanaged switches, the wiring defines the network. A device can communicate with any other connected device on the network. The standard network designs for Metasys Release 10.0 or later use managed switches to impose design rules. These rules complicate and clarify the network, and are described in further detail below.

One goal of networking is to provide segmentation. BACnet uses broadcasts for device discovery. Before IP controllers, the scope of broadcasts was mostly limited to one MS/TP trunk. The limit was imposed by the physical configuration of the network. For IP networks, the limit is imposed logically instead of physically. Each device receives an IP address and a subnet mask; the address seen through the mask identifies the subnet. Defined this way, a subnet exists in OSI Layer 3. A VLAN is defined in OSI Layer 2. For Metasys , you define VLANs and subnets so that they overlay exactly. If two devices are in the same subnet, they are also in the same VLAN; if two devices are in the same VLAN, they are also in the same subnet.

All the devices on a ring have to be in the same VLAN. A network engine can supervise devices in more than one VLAN. In the example shown in Figure 1, the simplest design is to place all of the controllers in the same VLAN, including the single controller that is connected to the switch but not part of the ring. There is no benefit in creating a second VLAN if it has only the one controller in the Mechanical Room.

The network engine can be in the same VLAN as the controllers, or in a separate VLAN. In the example in Figure 1, it is in a separate VLAN. In Metasys Release 9.0 networks, a BACnet/IP Broadcast Management Device (BBMD) may be required to rebroadcast communications between VLANs. In Release 10.0 you can configure a controller as a BBMD. Alternatively, you can configure the switches to forward BACnet broadcasts from the network engine to the subnet in which the IP controllers reside. You must consider the design of the network as a whole, and you can use the Metasys IP Network wizard to guide you as you make some of these decisions. For more information on the design of Metasys IP networks, refer to the Metasys IP Networks for BACnet/IP Controllers Technical Bulletin (LIT-12012458).