Software Defined Networks |

Software Defined Networks

September 152014
Software Defined Networks

By Dave Cronberger, Cisco for Industrial IP Advantage

September 15, 2014 - Software defined networks (SDNs) are a hot topic at the enterprise-level. The reasons vary – but they’re piling up. The most promising – and potentially profitable – benefit of an SDN is its potential in making the network directly programmable.

Imagine using an SDN controller to send messages to switches and routers to determine which ports are on, how the data is flowing and so forth. It operates in a similar way to a PLC that might tell a drive to start, slow down or speed up – by controlling the flow programmatically.

Today, SDN networks are in their infancy in the enterprise and are foreign in the industrial space. However, SDN concepts hold the potential to streamline the network architecture on factory floors.

As industrial networks move from serial-based communication to Ethernet, and as those Ethernet network devices become more sophisticated, monitoring and management become more critical. Having network devices participate as another path element variable in the control application simplifies the use of these new, sophisticated features and adds overall value to the manufacturing process.

SDNs simplify the configuration and implementation of network architectures by creating reusable configurations and designs that improve system performance. This simplification improves corporate margins because plants don’t need to rely on network specialists on the factory floor, thus lowering personnel costs, improving implementation time, and reducing troubleshooting and repair costs.

Present Versus Future Networking
The current method of managing a network separate from the application, and at scale, is inefficient.

A network is configured via a command line interface or a web browser on a node basis. Even with the use of web interfaces on newer switches, nodes are configured individually and remain static. A network specialist then must help the control engineer create a process solution for the plant. To avoid this complexity, some controls engineers turn to unmanaged switches – thus creating an unintelligent network environment.

But with the use of SDNs, users can manage, configure and control the network through a single controller. This in turn provides a “touch one, configure many” system through the use of automation verses the current “touch many, configure many” model.

The Role of Ethernet
The implementation of an SDN requires the use of Ethernet across the plant floor. Ethernet network devices all contain a management capability, a control capability and a data capability. Network Engineers often refer to these three parts of a network device as “planes” in order to think about them across many devices. The management plane facilitates monitoring and remediation, while the control plane focuses on the behavior and characteristics of the network and how things operate. Meanwhile, the data plane focuses on the transport of the information through the network.

Traditionally, each network device must be touched to configure and manage each of these planes. Because the control plane is used to configure individual devices, it gets touched the most. This constant interaction contributes to the complexity inherent in most industrial automation networks today. This complexity in turn can open the door to human error, which can trigger downtime and losses to the bottom line.

An SDN will help eliminate these risks. That’s because the control plane will exist in the SDN server, separate from the network node. From there, all devices can find it. Additionally, the network doesn’t need the server to operate, so any loss of connectivity to the server won’t disrupt any cell or zone network. This is especially beneficial in an industrial manufacturing environment, where network downtime can cost thousands, if not millions of dollars.

In transitioning to a software-defined network, the key challenge involves changing traditional practices on the plant floor. The typical factory includes specialists in areas ranging from robotics, to welding, to conveyor control.  These workers are well versed on how to deliver solutions in their areas. But they’re typically not trained network experts. So, for example, if a switch fails, an electrician is expected to quickly fix the switch to keep production moving. To do that, many factories use unmanaged network equipment because it’s easy to change. However, if it’s not a hard failure, the problem can be difficult for a factory floor worker to find and troubleshoot. They could call in IT, but that often creates a sense of tension.

Manufacturers must address this expertise gap to successfully implement and maintain a more intelligent network. That means providing these employees with the tools and knowledge they need to easily move toward a new, more intelligent infrastructure. In the end, the skilled trades are a critical part of the repair and replacement of equipment in the factory.

Machine design is another area that must be addressed differently. When machine builders construct a solution, the individual components used for the machine are not often questioned. However connecting the machine to the existing programmable automation controller (PAC) can be a challenge when Ethernet is not used and standards are not followed. Some machine builders leverage technology that is so disruptive to systems in the plant that redesigns are required of those other systems. To address this, it is critical for manufacturers to specify that the wireless and Ethernet components communicate seamlessly with the other systems.

Conceptual Architecture
SDN as an architecture is based on a set of programmatic abstraction layers that will be transparent to the controls engineer (see Figure 1).

Currently, these layers – as used in data centers – allow end-users to define a complete network within a set application without help from IT. SDN bases itself on open-source initiatives, offering the opportunity for anyone to create and market systems for industrial manufacturers in the not-so-distant future.

Specifically, automation control manufacturers, machine builders and end users will be able to create specialized and generic applications that add more value to the process control solution by making better use of the industrial Ethernet and wireless network.

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