The Tough Connection

With Ethernet increasingly becoming the choice network for the factory floor, Eddie Lee & Andrew Hsu discusses the factors to consider to ensure it works as well down there as it does up in the office.

The capabilities of Ethernet, despite the shortcomings of the technology when it was first developed over 30 years ago, have been dramatically enhanced in recent years. New advances in technology are constantly being applied to Ethernet to accommodate the requirements of industrial networking.

As a result, “industrial Ethernet” adds value in industrial automation network architectures by streamlining communication and interfaces, simplifying integration, and improving access to information without compromising network security.

Unfortunately, new technologies and implementations can also deter users from taking the risk of trying “bleeding edge technology.” According to David Humphrey, Senior Analyst at ARC Advisory Group, “Many end users still have no clear strategy as to how plant maintenance and IT should manage and share responsibility for factory network and device maintenance when industrial Ethernet is employed.”

For many, the first step should include determining the key goals of the network followed by selecting the proper equipment to facilitate achieving those goals.

Setting goals

What are the critical elements of the network and what benefits will be attained by a successful implementation? Goals for industrial networks can range in complexity from simple consistent data transfer between a few devices to redundant mission critical communications involving high speed performance and large bandwidth applications.

For example, in order to get away from a master switch representing a single point of failure for the entire network, communication redundancy may become a top goal or necessity. If the facility is migrating to an Ethernet/IP

network, the ability to handle multicast traffic (e.g. IGMP Snooping) becomes a priority. If the PROFInet protocol is in the plans, Quality of Service (QoS) for prioritization becomes integral. Thus, different goals and benefits require the careful selection of Ethernet infrastructure components with targeted features.

Besides cost, is there really an appreciable difference between Industrial v Commercial grade networking equipment? Some of the key differentiating factors are discussed below.

Different environment

Ethernet’s long time availability in the commercial environment long before industrial Ethernet equipment existed means that Ethernet office grade equipment is well accepted and known for it performance.

When connecting Ethernet components on a plant floor, the temptation might be to select similar, office-grade Ethernet devices from a local consumer electronics retailer. This type of equipment is certainly inexpensive and familiar to most people. However, what is commonly forgotten is the intended environment for which the commercial grade equipment was designed. Sitting on a desktop in an air conditioned home or server room is a far cry from the challenges facing networking equipment needed in an industrial control panel on a plant floor.

Hence, industrial Ethernet components are specifically designed to operate in plant floor environments. The specifications of industrial Ethernet switches –temperature, immunity to electromagnetic interference, shock, vibration, etc, often exceed those of the devices being connected (PLCs, HMIs, etc.), and can be two to three times stronger than the ratings found in comparable office grade equipment.

Industrial Ethernet switches also carry a Class I Div 2, group ABCD rating while the commercial counterparts do not. This allows the Industrial Ethernet switches to operate in hazardous locations where combustible gases or particles may be present – common in markets such as oil & gas, chemical, mining, pulp & paper. Furthermore, industrial Ethernet switches are housed in rugged metal enclosures using DIN-rail or panel mounting options. Most commercial switches cannot mount conveniently inside control panels without the inefficiencies of building a shelf and strapping the unit in place.

Switch not hub

A hub, also known as a repeater, is a simple device that connects Ethernet nodes. Hubs forward data packets they receive from a single device to all of its ports. Moreover, devices connected to a single hub or interconnected hubs share the same bandwidth. As nodes are added to the network, they compete for a finite amount of bandwidth (typically 10 or 100 Mbps). As a result, data collisions can occur frequently when hubs are used. Consequently, network determinism – the ability to guarantee that a data packet is transmitted/received in a finite amount of time – is not possible.

The primary reason Ethernet was not readily accepted in industrial control applications in the past can be attributed to this lack of determinism. Most control systems have a definite time requirement for packet transmission. This cannot be guaranteed with a hub and is especially unlikely if the network is busy.

On the contrary, an industrial Ethernet switch, is a more complex device with the intelligence to connect Ethernet nodes. The switch eliminates the problem of network determinism by providing full bandwidth with storage to a node or group of nodes. The switch can eliminate the collisions that previously made Ethernet non-deterministic. Unlike hubs, switches can recognize the physical or "MAC" address of a device and regulate message flow accordingly.

When a message frame reaches a switch, the switch checks the destination address against an internal Learned Address Table. If the destination address corresponds to one of the devices attached to the switch’s ports, it forwards the message specifically to that port. Message frames addressed to devices elsewhere on the network are passed to the appropriate switch on the network. The architecture of switches also permits multiple simultaneous transmission paths which significantly improves bandwidth.

Reliability & diagnostics

Network downtime can be dangerous and expensive. Industrial Ethernet networks must thus be highly reliable and continue to operate during harsh environmental conditions, accidental network disruptions, and equipment failures. Consequently, something as simple as an alarm contact to signal a communications failure or cable damage is commonly found on industrial switches and not available on office grade switches.

A basic redundancy requirement for control systems is that every part of the communication network should be hooked up to a backup power supply in case of a power outage. For example, to provide operation even during loss of a power supply, Moxa products support dual redundant power inputs, which ensures that no single power supply failure can bring the network down.

Reliability is also provided through media redundancy, coupled with firmware in the network devices that instructs the network to switch to alternate paths upon specific failures. Media redundancy, which involves forming a backup path when part of the network becomes unavailable, is a basic requirement for automation.

One of the first technologies developed for media redundancy, IEEE 802.1D Spanning Tree Protocol (STP), uses an Ethernet ring topology with backup paths. In the early years, it was not possible to create an Ethernet ring topology since loops in an Ethernet network are not allowed.

What IEEE 802.1D does is to identify one of the switches in the network as the “root switch”, and then automatically block packets from traveling through any of the network’s redundant loops. In the event that one of the paths in the network is disconnected from the rest of the network, the STP automatically readjusts the ring and uses the redundant path. The actual topology of the redundant ring (i.e. which segment will be blocked) is determined by the number of switches that make up the ring.

Although IEEE 802.1D STP has solved some limits of Ethernet network technology, it also has limitations, including lower convergence speed, constraints of bridge diameter, VLAN insensitivity, and link blockage (when the bandwidth is not enough for all traffic).

For this reason, IEEE 802.1W Rapid Spanning Tree Protocol (RSTP) was developed. This newer protocol has all the advantages of IEEE 802.1D, but provides higher performance (less than five seconds recovery time).

Ethernet device manufacturers are developing proprietary protocols based on 802.1W to meet the fast recovery time required in industrial automation. Moxa joined this movement by presenting customers with the Turbo Ring, which is able to provide a recovery time of under 20 ms at a full load of 250 devices.

Network management

As the size of a plant Ethernet network grows, and the number of networked devices increases, it becomes increasingly important to be able to monitor and verify the health of the network in real time.

Simple Network Management Protocol (SNMP) was developed to allow a network administrator to be able to configure and monitor, from a central management station, the distributed switches, PCs and other network infrastructure equipment while they operate. The SNMP management station displays critical data about the health of the Ethernet system, such as port link status, network errors, and network traffic information.

The real-time data regarding network health is gathered by polling information from SNMP agents in the network infrastructure devices. As a result, a network administrator can anticipate and reduce problems in the network.

Not all network devices are manufactured with embedded SNMP agents. Moxa offers both SNMP-managed switches as well as simple plug and play unmanaged switches.

In addition, since many industrial users already have powerful HMI data acquisition and control software packages that offer control of process equipment connected via the industrial Ethernet network, SNMP-OPC "gateway" software packages are available. These packages allow the existing HMIs to become the Ethernet network management interface.

Security concerns

Network security is quickly becoming the next great challenge for today’s

industrial automation engineers. The main task of a network security system is to allow only communication that is necessary for the information flow. Any

other data exchange is prevented by appropriate filters. Three primary areas of concern are:

• Integrity

Protecting network packets from modification by other parties

• Confidentiality

Keeping unauthorized users off the network, and keeping eavesdroppers within range from gaining useful information

• Availability

Low level Denial of Service (DoS) is hard to prevent

Unfortunately, there is no “silver bullet” to address all of the potential security concerns within an industrial Ethernet network. Before designing a security plan, knowledge of the communication relationships in the network is required. Specifically, which devices need to communicate to what, when should they be allowed to communicate, and where will they be located on the network?

Threats from outside the network (e.g. the Internet) can often be countered successfully using routers/firewalls and constantly updated virus scans. In most instances, a firewall or firewall with a virtual private network (VPN) acts as the main obstacle for unauthorized access to the network from an external threat.

Internal factors offer different risks. For example when the network is overloaded due to faulty devices or operating errors, firewalls will offer little relief. Managed switches (in the same network as the firewall) with features such as rate limiting or VLAN capabilities can help limit the damage or at least isolate the effects of the problem.

Additional switch features including password protection, port locking, and MAC ID filtering can also alleviate the likelihood of network trespassing or inadvertent tampering.

Leading technology

With the recent growth and popularity of Ethernet networking in both factory and process automation, engineers are tasked with selecting optimal yet cost effective infrastructure components from the litany of vendors and models available in the marketplace. Take into consideration the rapid rate by which networking technology is advancing, and it’s no wonder that confusion and fear of selecting the wrong components can paralyze even the most seasoned automation engineer.

And with Ethernet undoubtedly becoming the leading technology to provide seamless communication between the enterprise network and the plant floor network. The technology available for industrial automation will continue to improve and change.

Nonetheless, the basic considerations used in selecting the proper infrastructure components will remain fairly consistent. There are now a vast assortment of industrial Ethernet solutions available on the market to help form the foundation of a highly reliable industrial automation network and able to meet the demands of today with the versatility and flexibility to adapt for tomorrow.

Eddie Lee is currently Product Marketing Manager, Moxa Technologies; Andrew Hsu, is currently Product Sales Manager, Moxa Networking (www.moxa.com).

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Boosting the Bandwidth

With Belden’s acquisition of German industrial Ethernet specialist Hirschmann Automation and Control making the headlines earlier this year, Asia Pacific head Naresh Kumra tells CE Asia all about the company’s bold ambitions.

Prior to joining Belden as Vice President, Business Development, Naresh Kumra was Associate Principal, McKinsey & Co, where he was responsible for private equity and growth and innovation practices. He also previously worked for Schlumberger Industries, in India and France, as a software engineer, manufacturing manager, and product line manager. In June 2006, Belden appointed Kumra to his present position of President, Asia Pacific.

In recent months, Belden has made headlines with a number of high profile acquisitions: Hirschmann Automation and Control (HAC), LTK Wiring, and Lumberg Automation.

CEA: It seems to been a very busy time for Belden recently. What was the trigger for this burst of activity?

Kumra: The merger with CDT in 2004 propelled Belden into the billion dollar plus (annual revenue) league of companies, and playing at the level and to take the company forward, the board decided it was necessary to refresh the management team and include individuals with experience in the industrial field, although not necessarily with a background in cable.

For myself, coming from a strategy background at McKinsey, one of my tasks was to introduce a proper strategic planning process to the company and engage the leadership to buy into it. Now everything we do is in relation to the strategic plan that was developed.

CEA: And what is that plan?

Kumra: It comprises a number of elements in a three-level approach: Strengthen the Core; Grow the Core; Expand the Core.

Strengthen the Core elements include Talent Management – getting good people and giving them opportunities; Brand Management – repositioning from a cable company to a signal transmission solutions company; and Regional Manufacturing – having manufacturing centers of excellence in each major continent.

Grow the Core is all about increasing our scale and capitalizing on growth in emerging markets. And Air, Light & Connectivity in Expand the Core signifies the desire to offer signal transmission over all media – wireless, fiber, copper.

CEA: What was the rationale behind the Hirschmann acquisition?

Kumra: The Hirschmann product range of industrial Ethernet components and industrial connectors for sensors and actuators is highly complementary to Belden’s industrial cable product line, and the acquisition fits into our strategic plan of expanding our overall connectivity portfolio and being able to provide a total solution to customers. The company also has wireless technology and products.

Because there is a wide range of industrial connectors, one acquisition was not enough; hence the subsequent purchase of another German company, Lumberg Automation, to give us what is now a very broad industrial connectivity portfolio.

CEA: These are both German companies. A coincidence?

Kumra: Many of the leading machinery manufacturers are located in Germany and Switzerland, and both Hirschmann and Lumberg have many decades experience supplying products to demanding companies like these. Thus, they have considerable technological expertise, and when we were identifying acquisition targets, innovators like these were preferred over technology followers.

CEA: Your take on industrial Ethernet?

Kumra: The industrial Ethernet market is growing tremendously. Drivers include the rollout of new manufacturing facilities, especially here in Asia, and the desire to link the enterprise and factory via a single, cost-effective network. Hirschmann is already the global market share leader for rail-mounted industrial Ethernet products, and we anticipate increasing adoption by customers in the years ahead.

CEA: Presumably the acquisition of LTK Wiring strengthens your position here in Asia?

Kumra: Yes, absolutely, and it also satisfies the strategic goals of growing in emerging markets and having manufacturing capability close to customers. LTK Wiring, which supplies a wide range of wire and cable products, is headquartered in Hong Kong, has production plants in Shanghai, Dalian, Huizhou, and an extensive sales network throughout Asia.

This acquisition really changes the game for Belden here in the region. We have quintupled our business in Asia overnight, have access to extensive, lower cost manufacturing resources, along with a pool of talented people familiar with Asia.

CEA: It sounds like an exciting time at Belden. What more can we expect?

Kumra: The organization is certainly reenergized and we are set to charge ahead further. Even after the three acquisitions, which have all been successfully completed now, Belden is in a strong financial position.

We are a company that wants to lead and win, and do it in a way to help our customers. Belden products are used by brand name clients like Sony, Dell, Google, GE, Boeing, etc, and we see ourselves as helping shapers to shape the world, and as leaders helping other leaders to succeed.

For rough, tough environments

Ethernet switches

Dual redundant power inputs

The switch

Naresh Kumar

Belden's strategy

Hirschmann