1 September 2002

Industrial Ethernet gaining factory floor strength

By Manrique Brenes

Rugged technology delivers reliability, security, and intelligence

The move to Ethernet on the factory floor has been growing steadily, as large enterprises move to what is clearly now the network of choice on the factory floor.

This migration to a single, standards-based technology is the natural progression to more open architectures, as manufacturers strive for more efficient and cost-effective plant floor technologies.

Backed by a wide array of plant equipment vendors, industrial Ethernet–based systems allow manufacturers to standardize and consolidate different manufacturing network architectures prevalent in many factories today. This natural convergence (already completed in the front office a decade ago) provides process engineers with greater economies of scale, vast technological innovation resources, and intelligent features that dramatically increase control over the array of manufacturing devices linked by the control network.

"We fully promote Ethernet as a technology for plant floor manufacturing systems," said Doug McEldowney, NetLinx strategic marketing manager for Rockwell Automation. "This open, widely deployed standard networking technology, coupled with an open, accepted industrial application layer protocol—the Control and Information Protocol, or CIP—provides tremendous flexibility and functionality to the shop floor in EtherNet/IP solutions for a wide variety of applications."

As a result, companies are able to reliably transmit information intelligently and securely throughout the company. These capabilities will eventually facilitate an end-to-end flow of information, letting manufacturers achieve tremendous efficiencies and productivity.

Today, separate networks

Today, many manufacturing companies maintain separate networks. Over the years, these networks took shape to respond to diverse information flows and control requirements.

The corporate information technology network supports traditional administrative functions, such as human resources, accounting, and procurement. This network is based on the ubiquitous Ethernet standard.

The control-level network connects control and monitoring devices, including programmable logic controllers, PC-based controllers, I/O racks, and human-machine interfaces. This network, which has not been Ethernet in the past, requires a router or, in most cases, a gateway to "translate" application-specific protocols to Ethernet-based protocols. This translation allows information to pass between the control network on the factory floor and the corporate network infrastructure, which otherwise are not connected.

The device-level network links the plant floor’s I/O devices, such as sensors (transducers, photoeyes, flowmeters, etc.), and other automation and motion equipment, such as robotics, variable frequency drives, and actuators. Interconnectivity among these devices has traditionally been achieved through protocols that have been highly reliable but are somewhat limited in terms of data throughput and interconnectivity with upper-level networks.

These networks evolved to support different types and streams of information as well as high noise and environmental conditions. There are, however, several disadvantages to maintaining multiple networks based on various traditional fieldbuses.

Lower efficiency and productivity: Due to the nature of most traditional non-Ethernet control networks, it is difficult to share data between the factory floor and the higher-level software entities—enterprise resource planning (ERP), manufacturing execution systems—without a gateway that mediates between the corporate network and the factory floor. This gateway limits implementing real-time scheduling, monitoring, and maintenance systems.

Higher costs: Traditional manufacturing systems usually have their own Layer 1 (cabling and signaling) transmission architectures. These interfaces tend to have higher costs and fewer suppliers.

Higher complexity and training duplication: Most organizations have already developed skills around Ethernet to support their corporate network. Ethernet-based control systems can use this expertise and concentrate on developing networking skills around a single network architecture shared by multiple control equipment vendors, reducing the level of complexity created by multiple networking platforms.

Bandwidth and network addressing limitations: Shared bandwidth available today for a large part of traditional control networks is normally measured in kilobits per second, with the fastest implementations sharing 12 megabits per second (Mbps) between multiple nodes. This amount of bandwidth limits the potential to transmit real-time data and makes it virtually impossible to incorporate devices (such as digital cameras) that demand significantly more throughput. Even if greater bandwidth were available, there is no link or structure that can associate a given device to an IP addressing scheme, which limits polling data (diagnostics, health monitoring, etc.) to within the network itself.

Enter industrial Ethernet

Industrial Ethernet provides a more robust solution that lowers costs, boosts productivity, and streamlines system complexity. It is based on an inexpensive and universally deployed data link standard.

Ethernet has long been considered an alternative for data transmission on the plant floor. Its acceptance, however, grew dramatically in recent years, thanks to the emergence of impressive reliability. For example, network consortia such as the Open DeviceNet Vendor Association are including details for industrially hardened Ethernet cable systems in their specification.

While data-oriented networks, such as ones used in offices, were designed to maximize bandwidth, control- and device-level networks were optimized to obtain a very deterministic performance with very low latency. Ethernet’s early, collision-oriented implementations made the level of determinism unacceptable on the plant floor.

Today’s Ethernet installations (100 Mbps, full duplex in a switched network) show latency measured in microseconds—many orders of magnitude better than most factory floor reliability requirements. Therefore, a multiple network structure is difficult to justify as current Ethernet implementations meet and/or exceed the throughput, reliability, resilience, and determinism required by the factory floor.

Different approaches have been used while deploying Ethernet-based architectures.

Industrial Ethernet’s advantages

Ethernet-based control applications are perfectly suited for challenges manufacturers face today and far into the future. Simply put, industrial Ethernet is able to unite a company’s administrative, control-level, and device-level networks into a single system.

Enhanced productivity and efficiency: With a more integrated network, mission-critical information can flow freely and in real time throughout the company. As a result, manufacturers experience great gains in collaboration, efficiency, and work quality. In addition, companies may choose to share data from their plant floor process with other business partners, turning their businesses into e-businesses. With an Ethernet network supporting an IP addressing scheme, a company has the ability to collaborate electronically with suppliers, customers, and contractors. The partners can enjoy far better access to certain information such as order status and shipment dates, which they can access in real time right from their own desktops.

Reduced costs: A standard Ethernet interface brings to the factory floor the economies of scale enjoyed today by hundreds of millions of Ethernet users, lowering costs and increasing the number of potential equipment vendors and products for a particular manufacturing application. In some instances, potential cost reductions can reach an order of magnitude.

Greater bandwidth and overall functionality: Ethernet delivers shared bandwidth far in excess of today’s networking systems—typically at full-duplex 10 Mbps to 100 Mbps using switching technologies that can guarantee the throughput to all nodes hooked into the network. This capability allows networks to deliver substantive, actionable information. An Ethernet network, for instance, allows transmitting detailed control information in real time to a company’s ERP system. With enough bandwidth, additional applications can even be added to the network, including those requiring simultaneous data, video, and voice transmission.

Streamlined network structure: A single network eliminates the need to implement, support, and maintain three or more separate systems, reducing overall network costs and improving information access.

Manufacturers no longer need to endure the high costs and limited functionality of maintaining multiple separate networks. Industrial Ethernet has the potential to deliver a single, high-quality network throughout the entire enterprise, substantially lowering costs and boosting capabilities companywide.

Intelligent services added

Companies should be careful to select Ethernet products that add vital intelligence to their networks. Industrial Ethernet has many advantages over proprietary technology that exists in many manufacturing environments. But be advised: Not all Ethernet solutions are created equally.

What do we mean by "intelligence"?

Specifically, an Ethernet-based solution should provide additional services that make the network highly functional, manageable, and secure. For industrial environments, these intelligent services should include the following:

Advanced security: A variety of mechanisms exist to secure Ethernet networks. Manufacturers should deploy robust security mechanisms to prevent outside intrusion, as well as ensure that internal communications remain private.

Virtual LAN: Support provides security and isolation by virtually segmenting factory floor data from all other data and users.

Port security and access control lists: At different layers, they provide granular and secure filtering. This capability allows a network administrator to prevent/allow access to information based on its source, destination, and type of application. Access can be based on physical parameters (for example, port number or MAC address), IP address, or TCP/UDP port (essentially determining whether the packet is from an application that should be running on the network).

Fast Spanning Tree: The Spanning Tree protocol permits the rapid convergence of a network. If a problem occurs on a network node, a redundant alternate link will automatically come back online. With Fast Spanning Tree, networks converge very quickly, and node will become available again in less than 1 second. This is known as "subsecond convergence." Previous Ethernet deployments lacked this feature (leading to convergence times higher than 50 seconds). Fast Spanning Tree has now been sanctioned by the Institute of Electrical and Electronics Engineers.

SNMP support: The simple network management protocol (SNMP) forms the basis of virtually every major network management system. Intelligent Ethernet devices must support SNMP, allowing it to interface with a company’s existing management system or with commercially available management systems.

Quality of service: An industrial Ethernet network may transmit many different types of traffic, from routine data to mission-critical control information to bandwidth-hungry video or voice. The network must be able to distinguish among and give priority to different types of traffic. Quality of service mechanisms do just that. They ensure all traffic receives the required bandwidth, priority, and latency so the network runs smoothly and efficiently.

IGMP snooping: Internet group management protocol (IGMP) snooping allows multicast traffic to be easily managed in a switched network. Without this feature, the potential exists for flooding the control network with multicast traffic. IGMP snooping becomes critical for control applications that use a producer consumer model (a network element producing a stream of data used by one or more consumers).

For manufacturers, networks must be available, reliable, and secure. At the same time, network elements must provide highly intelligent features that allow companies to take advantage of the flow of information available today within their networks.
Industrial Ethernet fulfills these requirements—and more. WBJ

Behind the byline

Manrique Brenes is a product manager for Cisco’s Desktop Switching business unit in the Ethernet Access Group.

Coming Next

Ask The Experts

Read questions answered by our experts or join the email list.