The ten commandments of EtherNet/IP
One of the biggest trends in today’s modern manufacturing environment is the move towards open and fully conversant automation systems. And without a shadow of doubt, one of the biggest enablers has been the introduction of Ethernet into the industrial environment. Indeed its introduction has had a profound impact on industry. But can Ethernet really be all things to all people?
It is often argued that off-the-shelf commercial Ethernet and IP solutions lack the degree of determinism and predictability required for industrial control. To overcome these perceived shortcomings, several Ethernet or Ethernet-based systems have been developed for industrial use. One – EtherNet/IP – offers the industrial optimisation of a specialised control network with the openness and flexibility of standard Ethernet, taking advantage of today’s Ethernet technology without resorting to modified switches, silicon or stacks.
The decision to put Ethernet on the factory floor should not be taken just because it works, instead it must be because there is a business case to add automation to the growing long list of services that are currently being carried over the existing infrastructure. Rockwell Automation, one of the suppliers of the EtherNet/IP devices and solutions, takes those on the cusp of making a migration decision through a simple checklist of factors that must be considered.
The decision to put Ethernet on the factory floor should not be taken just because it works, instead it must be because there is a business case to do so.
Without an understanding of what you actually require and, more importantly, what you want it to do, the installation could either be under or over specified or, indeed, not suitable for your application. At system environment level it is important to gauge what type of plant floor control is needed and how it would integrate into an IT network. The ability to future proof the system to a greater or lesser extent must also be considered, with expandability being at the top of the list.
Performance is another major system issue. The amount of data being carried over the network and how fast it changes can have a big impact on its architecture. With Ethernet, this is not just limited to automation data, but all of the data needed to manage a business. Users must not only consider the media being used to transfer all of this information but also hardware and software factors such as switches, routers and firewalls.
Step 2: Learn the system environment
Only by learning the system environment can you get an idea of the levels of complexity. The primary question to ask is: Will your automation system be integrated (free exchange of all types of data), connected (exchange of automation only data) or isolated (no exchange of information) from the IT system? Only by asking this question can you make judgements on the benefits that you will get from, and the level of complexity of, the potential system.
Step 3: Make IT Aware
Automation applications create a great deal of I/O control data – traffic that can impact the rest of the IT enterprise. Good network design and implementation will help resolve all of these issues but IT departments can’t take these steps if they don’t know what is happening on the factory floor. This gives you the opportunity to address other internal issues that may also arise: Who owns the network? Who is responsible for maintenance? Who assigns IP addresses?
Step 4: Segment networks properly
It is important to undertake proper traffic segmentation. Not only will it simplify network management but it also maximises backbone or control network availability. It is also possible to deal with security issues at this level. Segmentation can be achieved by two means; either a physical segment can be used, such as a switch, or logical segments can be created using a virtual local area network (VLAN) or IP Subnets.
Step 5: Thou Shall not use hubs
Hubs or repeaters can allow data collisions – a particularly unattractive feature for control networks; this is why switches and routers are more attractive propositions. A switch will not only eliminate the possibility of collisions but it will also segment traffic within an IP Subnet, while routers help segment networks and traffic.
Rockwell Automation has an enviable depth of expertise and knowledge when it comes to automation installations and the associated networking hardware, software and media.
Ask these questions: What is the switch expected to deal with? Is it suited to the operating environment? And, what type of data will it be handling (commercial or industrial)? It is also important at this stage to define what is required, what is recommended and any elements that may make up part of a “wish list”.
There are a number of features that are prerequisites for EtherNet/IP switches, these include: full-duplex capability on all ports; IGMP snooping, to constrain multicast traffic only to ports associated with a particular IP multicast group; and port mirroring, the ability to direct a duplicate of the frames being transmitted on one port to another port for troubleshooting. Switches that fit these criteria are available from a number of Rockwell Automation Encompass partners.
Step 7: Select and install the right media
You must ensure that suitable media is used for the transmission of data. Users have a choice of two, each of which has its own advantages depending on the application. CAT 5e and 6 copper cables and connectors are recommended for industrial applications. UTP (unshielded twisted pair) is generally recommended, while STP (shielded twisted pair) is recommended for metal conduits and noisy environment. It is important to ground one end only.
Fibre optics are good for noise immunity and long distances when connecting switches together. Single-mode fibre optic cable, through which only one mode will propagate, is more resistant to attenuation and can be used in significantly longer cable runs, while multi-mode fibre optic cable gives high bandwidth at high speeds over medium distances, and is a more of a general-purpose media.
Step 8: Understand end-device limitations
It is unlikely that traffic over a 100Mbps or 1Gbps infrastructure will be the cause of any bottlenecks. With high-bandwidth networks like Ethernet, the limitation on system performance is almost always due to the processing power of end devices. It is for this reason that end device vendors must provide performance information and calculation rules for their devices and users must factor all devices into the system calculations – not all end devices offer the same capabilities.
Step 9: Be aware of potential security issues
By sharing a network, information can be spread further and so security could become an issue. But, if it is managed and controlled from the outset, there is no reason why an Ethernet network should be any less secure than any fieldbus is today. In fact, use of standard Ethernet is an important tool to make business critical data and systems far more secure! And because it is using standard Ethernet, there are a wide variety of consultants (including Rockwell Automation) qualified to help get it right.
Step 10: Don’t hesitate to get help
Rockwell Automation has an enviable depth of expertise and knowledge when it comes to automation installations and the associated networking hardware, software and media. Organisations investigating the possibility of a move over the industrialised Ethernet should take advantage of this depth of knowledge, as it is more than likely that their questions have already been answered.
Remember, EtherNet IP is not difficult – it’s just different!
An important final note – while Ethernet is very versatile and can perform some functions that dedicated device-level networks cannot, it does not offer all the features of a purpose-built control network. So, for specific control applications requiring the robustness of ControlNet or the scalability of DeviceNet, an industrial Ethernet is unlikely to fit the bill and, as a result, Rockwell Automation remains committed to the development and support of products using these networks.
For more information visit:
http://www.ab.com/networks/ethernet/next-step.html
http://www.ab.com/networks/get/UnmanagedSwitches_07252005.pdf
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