Installation guide

Network Infrastructure for EtherNet/IP™
Designing the Infrastructure
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4.12 Achieving Deterministic Behavior
Different mechanisms can be implemented to achieve reliable and deterministic behavior on a network.
Scale and criticality are two key factors for determining when to implement such mechanisms. Just as a
back country road often can effectively move traffic and manage the potential for collisions with a single
lane, traffic in larger metropolitan areas generally demands multi-lane, multi-level highways. As the
amount of traffic increases, the need for mechanisms that can guarantee a given performance becomes
evident.
In general, two factors drive the need to implement performance mechanisms in EtherNet/IP networks.
•
Scale: Small networks that will not be sharing their resources with other applications,
such as video, voice, non-control data, etc. have lower potential for congestion and
consequent jitter, latency, and frame losses. As the networks grow and the hosts begin
sharing data through a producer-consumer model, the need for mechanisms such as
IGMP snooping and QoS become indispensable to guarantee a deterministic behavior.
•
Criticality: Some applications can tolerate lost data without any significant impact on the
manufacturing process, and other applications can be adversely affected by even small
latency or packet loss. Even small disruptions can have a big economic impact on a
manufacturing facility. In these cases, it is normally a requirement to implement cost-
effective solutions that reduce the potential for a work stoppage.
Large EtherNet/IP deployments or deployments where a line stop is critical should consider
implementing:
•
A fully switched network. This will eliminate collisions and improve the deterministic
behavior of the data network.
•
Quality of Service (QoS) traffic prioritization. QoS prioritization allows time critical
traffic to have preferential handling over supervisory traffic.
•
Logical segmentation of the network. VLANs improve security and contain
broadcast messaging.
•
IGMP snooping. This will control multicast messages that can slow the performance of
the network hosts. It also exponentially reduces the amount of traffic on the network,
reducing the chance for congestion and consequent packet loss.
4.13 Managing the Interface between Control and IT
Managing the interface between control and IT requires cooperation between two disparate sets of needs.
Covered here is the technology of integration—connecting EtherNet/IP networks to enterprise networks.
There is no doubt that EtherNet/IP networks can solve the “islands of automation” syndrome that has
plagued manufacturers for so long, but making them work with the enterprise network will require a
commitment for cooperation between a manufacturer’s enterprise Information Technology Department
and plant-floor network engineers.