Industrial Ethernet Managed Switches Configuration
Original instructions
About us
Open Network Convergence Configuration
A typical M580 system provides deterministic services to RIO drops by using, among others, the RSTP protocol for network convergence in case of link loss. Usage of service port only in an open Ethernet network eliminates RSTP capability.
As the Ethernet link loss is the main trigger for network convergence, configure the industrial Ethernet managed switches for optimal network availability.
In this context, the detection time is defined as the maximum time by which the open Ethernet network should detect communication loss and appropriately converge to avoid operational impact.
The maximum recovery time supported by the industrial Ethernet switch network has to be taken as reference to configure the parameters that define the detection time of the communication between the M580 CPU and the BM•CRA31210 adapter modules.
Improper configuration of network convergence (network convergence period is greater than scan rate) leads to an indeterministic network and loss of communication.
Refer to chapter Communication Loss Detection Times to determine the detection time value of communication loss.
Setting Traffic Priority
Traffic priority is managed in 802.1Q Ethernet frame header of the packets by setting:
The following figure represents a typical 802.1Q Ethernet frame header:
VLAN Identifier (VLAN-ID)
VLAN is used to provide virtual isolation of traffic on the network.
Network traffic with a unique VLAN-ID is produced/consumed by only the devices configured for this VLAN.
NOTICE
LOSS OF CONNECTIVITY WITH THE RIO DROPS
Do not assign the same VLAN-ID to X80 RIO drops managed by different M580 CPUs.
Failure to follow these instructions can result in equipment damage.
Assign as many as necessary VLAN-IDs to create traffic isolation between the Modicon M580 CPU and its scanned X80 RIO drops and other modules.
To achieve this isolation, ensure that for every such M580 system being configured in the network, a single unique VLAN-ID is attributed to the switch ports to which the service ports of the modules are connected.
VLAN Priority Scheduling
VLAN priority scheduling is Layer 2 Ethernet switch functionality that prioritizes packet management in buffer overflow situations. For this open M580 architecture, we prescribe that, the lowest priority packets should be dropped from processing in the scenario of a buffer overflow at the industrial Ethernet managed switch level.
Quality of Service Configuration
In the industrial Ethernet managed switch, along with assigning unique VLAN-IDs, care should also be taken in assigning traffic priority to each type of Ethernet packets between the M580 CPU and the respective X80 RIO drops.
Configure the industrial Ethernet managed switches to assign appropriate 802.1p priority to every packet based on the DSCP value embedded in the packet. For example, RIO and CIP safety traffic have high 802.1p priority (that is 5) when traffic with DSCP value of 47 is received at the industrial Ethernet managed switch.
The following table gives the traffic priority to be set in 802.1Q header of the Ethernet packets in the industrial Ethernet managed switch, corresponding to the respective DSCP value:
QoS Level
DSCP Value
Traffic priority bit (802.1p)
Traffic usage
Network usage
Urgent
59
(111011 bin)
7
Network time protocol (NTP) messaging
Time synchronization between CPU and Remote I/O (X80 RIO drops, X80 RIO Safety drops)
Scheduled
47
(101111 bin)
5
Implicit (I/O and safety)
Remote I/O (X80 RIO drops, X80 RIO Safety drops) and CIP Safety devices)
High
43
(101011 bin)
5
Implicit (I/O)
Distributed I/O (DIO) (EtherNet/IP or Modbus TCP) or CPU to CPU communication
Explicit
27
(011011 bin)
3
Explicit messaging
All equipments (application based)
Other
0
(000000 bin)
and other DSCP values
1
Other traffic
Other Messages (for example, DHCP, SNMP, FTP, TFTP, IGMP, SMTP, ICMP, and so on.)
When the switch is configured for VLAN priority scheduling, the least priority packets are dropped. In consequence if Scheduled QoS level traffic such as RIO and CIP safety is not configured to the correct traffic priority (Priority 5), this can lead to a loss of data during buffer overflow scenario.
NOTICE
LOSS OF DETERMINISM AND DISCONNECTION OF THE RIO DROPS
Verify that the industrial Ethernet switch configuration strictly adheres to the traffic priorities given in the above table.
Failure to follow these instructions can result in equipment damage.