1. Using Intelligent Ethernet for Automation Control 

Context in source publication

Context 1

... 10BASE-T Ethernet delivers performance of up to 10 Mbps over twisted-pair copper cable. ● Fast Ethernet delivers a speed increase of 10 times the 10BASE-T Ethernet specification (100 Mbps) while retaining many of Ethernet’s technical specifications. ● Gigabit Ethernet : increasing speed tenfold over Fast Ethernet to 1000 Mbps or 1Gbps. ● 10 Gigabit Ethernet , ratified as a standard in June 2002, is an even faster version of Ethernet. Speed at 10Gbps Industrial Ethernet applies the Ethernet standards developed for data communication to manufacturing control networks (Figure 3.1). Using IEEE standards-based equipment, organizations can migrate all or part of their factory operations to an Ethernet environment at the pace they wish. For example, Common Industrial Protocol (CIP) has implementations based upon Ethernet and the IP protocol suite (EtherNet/IP), DeviceNet, and ControlNet (among others). Most controllers (with appropriate network connections) can transfer data from one network type to the other, leveraging existing installations, yet taking advantage of Ethernet. The fieldbus data structure is applied to Layers 5, 6, and 7 of the OSI reference model over Ethernet, IP, and TCP/UDP in the transport layer (Layer 4). Although Industrial Ethernet is based on the same industry standards as traditional Ethernet technology, the implementation of the two solutions is not always identical. Industrial Ethernet usually requires equipment that can handle more severe environmental conditions, flexible node counts, varieties of media, very predictable real-time data traffic performance, and increased levels of segmentation as compared to traditional Ethernet networks in a corporate data network. The primary difference between Industrial Ethernet and traditional Ethernet is the type of hardware used. Industrial Ethernet equipment is designed to operate in harsh environments. It includes industrial-grade components, convection cooling, and relay output signalling. And it is designed to operate at extreme temperatures and under extreme vibration and shock (and other conditions). Power requirements for industrial environments differ from data networks, so the equipment runs using 24 volts of DC power. To maximize network availability, Industrial Ethernet equipment also includes fault-tolerant features such as redundant power supplies. The equipment is also modular in order to meet the highly varying requirements of a factory floor. Ethernet Switches usually work at Layer 2 (data link) of the OSI reference model using MAC addresses, and deliver a number of important advantages compared to hubs and other LAN devices. ● Predictable performance: The ability to ensure that a packet is sent and received in a specific period of time is an important design goal for industrial networks. For the network to support predictable, real-time traffic, the design must be as simple and highly structured as possible. ● Increased speed up to 9.6kbits/s with RS-232 to 1Gbits/s with IEEE 802 over Cat5e/Cat6 cables. ● Standardization: One of the main motives for using Industrial Ethernet is the need to standardize a common infrastructure. ● Better interoperability. ● Managing a whole TCP/IP stack is more complex than just receiving serial data. ●The minimum fast Ethernet frame size including inter -frame spacing is about 80 bytes, while typical industrial communication data sizes can be closer to 1-8 bytes. This often results in a data transmission efficiency of less than 5%, negating any advantages of the higher bit rate. ● Some of the industrial Ethernet protocols introduce modifications to the Ethernet protocol to improve efficiency. At the physical layer, a number of techniques can be applied to help achieve a resilient, highly available network. First, the various components can be configured or purchased with resilient features such as redundant power supplies (or even UPS), and redundant components (such as fans, CPUs, network interface cards [NICs], etc.). Using redundant devices may also help maintain high network availability. For example, multiple switches or routers can be configured in a high-availability manner so that in the case of disruption of one device, the other device will take over the network services quickly and automatically. Two network topologies most often used to achieve higher availability are ring and redundant star. The topology chosen also has implications on wiring cost and complexity, performance, and installation and maintenance cost In redundant star designs (Figure 4.1), switches and routers are connected in a hierarchical fashion. The first layer where devices are connected to switches is often referred to as the access layer. These switches provide connections for endpoint devices such as PLCs, robots, and HMIs. Access-layer switches generally operate at Layer 2 (data link) of the OSI model. Above the access layer is another layer of switches referred to as the distribution layer. These switches interlink the various access layer switches. If they support multiple cell/area zones, they may need to operate at Layer 3 (network) of the OSI model, referred to as Layer 3 switches or routers, to support multiple VLANs. (Cisco, 2010). In ring topologies (Figure 4.2), all devices are connected in a ring. Each device has a neighbour to its left and right. If a connection on one side of the device is broken, network connectivity can still be maintained over the ring via the opposite side of the device. It is important to understand the physical environment and network performance requirements when determining the optimal network topology. The physical layout of automation networks is often different than a traditional IT environment, which may drive the use of the ring topology. Table below highlights the appropriate topology based on some common concerns (cisco, 2010): Table 4.1: table highlighting appropriate ...