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.
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