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CTI Janus Programmable Automation Controller IOG
NOTE
Broadcast and Multicast frames from the internal Ethernet interface will be forwarded to all frames. In the
majority of cases, this traffic is insignificant. Broadcast frames are primarily transmitted when resolving IP
addresses to MAC addresses. Once known, this information is cached. If you are sending substantial
multicast traffic, network switches can be configured to limit Multicast forwarding (using IGMP Snooping).
Alternatively, you may want to use only one network port.
Alternate IP Subnets
TCP/IP is responsible for functions such as routing IP packets among local area networks, establishing connections
between devices (IP Hosts), and associating IP addresses with Ethernet MAC addresses. As noted above, on
Ethernet networks, the TCP/IP protocol is contained as data in Ethernet frames.
An IP Host, such as the Janus controller, can communicate directly with other IP Hosts on the same Ethernet Local
Area Network only if they belong to the same IP subnet (see APPENDIX B: IP ADDRESS INFORMATION). Otherwise
IP packets transmitted by the device are sent to an IP gateway, which attempts to route them to another network.
Typically, a single set of IP address parameters (IP address and subnet mask) are associated with a
device’s
Ethernet interface. As a result, the device is limited to communicating directly with devices on a single IP subnet.
However, the Janus controller allows you to associate up to four sets of IP parameters with its Ethernet Interface,
enabling the controller to communicate directly with devices on four different IP subnets, if desired.
This capability is especially useful when connecting the controller to multiple Local Area Networks. See the
example below. For simplicity, separate Ethernet switches for each network are illustrated. This topology can also
be accomplished with one switch using VLAN (Virtual Local Area Network) technology.
Example
Port A is connected to a plant
“data” network
, used for programming and data access (HMI and SCADA
workstations). Devices on this network are members of the IP subnet 172.18.12.0/24 (172.18.12.1, 172.18.12.2,
etc.).
Port B
is connected to an “I/O” network
, used to communicate with Ethernet I/O. Devices on this network are
members of the IP subnet 172.18.13.0/24 (172.18.13.1, 172.18.13.2, etc.).
Janus
P
A
C
Ethernet Switch
PGM
HMI
HMI
HMI
I/O
I/O
I/O
I/O
Ethernet Switch
172.18.12.0/24
172.18.13.0/24
A B
C D
To Plant
Network
