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Q.
Ethernet is being deployed in new environments and for new solutions that traditionally have required very low
bandwidth. Why do they need intelligent services?
A.
Different issues are driving the move to Ethernet in multiple new markets. In general, the level of information
traversing networks is increasing as the hosts on these networks increase their functionality and users look for ways
of retrieving real-time data from the processes they are controlling and monitoring. Traditional proprietary networks
(fieldbuses) do not have the bandwidth to handle these new informational requirements, but they have traditionally
been very reliable and deterministic (based on token-sharing topologies). This has allowed for critical control traffic
to be delivered on time, but not much more.
As Ethernet-based solutions are deployed, critical traffic will be sharing the network bandwidth with non-critical
(data collection and configuration) traffic, creating the possibility that delay-sensitive information is affected as the
data traffic in the network grows. This will be aggravated by the addition of traditional applications (voice, video,
and e-mail) to a common Ethernet infrastructure, similar to the convergence of voice and data networks now
prevalent in the traditional LAN markets. By providing traffic prioritization based on the parameters of Layers 2–4,
a network administrator can guaranty that delay-sensitive and critical-control traffic always has precedence over
non-critical traffic.
Another element driving the deployment of Ethernet networks is the recognition that internetworking technologies
that allow for data sharing through various networks (internal and external) can be a competitive advantage for
an organization. With their industry-specific networking schemes, traditional field buses were essentially closed
networks and did not facilitate data exchange or intrusion into the networks. Industrial Ethernet deployments are
based not only on Ethernet, but also on IP addressing schemes that allow for new levels of communication and
information exchanges. This in turn requires a new set of policies and security services, which the Cisco Catalyst
2955 offers.
In a manufacturing operation, the automation process is the revenue engine of the organization. Network downtime
is easily equated to losses. It is critical that the network is highly available. Intelligent services such as fast spanning
tree, storm control, and multicast management are part of the services that provide the level of resilience demanded
by nontraditional Ethernet deployments.
Q.
Why is IGMP snooping important in manufacturing networks?
A.
New markets and applications may involve data flows that differ from traditional LAN deployments. Most
industrial Ethernet implementations rely on a producer-consumer model, where a host that needs to send data
(producer) to another device in the network (consumer) multicasts the information instead of sending a unicast
message to the device. This model was developed to ensure that if two or more devices (consumers) needed a set of
data, that all the devices requesting that data would have access to the same information at the same time. IGMP
snooping prunes the multicast traffic so that only the devices that need the information from a given consumer will
receive it. Without multicast management services, the traffic in the network grows exponentially with the number
of hosts that become producers. This not only overburdens the network, but may also stall the hosts receiving
unneeded traffic. Many I/O devices common in industrial networks have limited processing power and will not be
able to process multiple streams of unneeded data—potentially choking these devices.
