Tips for understanding ‘IT-speak’
In most plants, there has traditionally been a communications gulf between maintenance and IT. That’s largely been fine, except that now, increasingly more process controls are connected to industrial networks, and plant engineers are experiencing network-type problems that cause downtime and affect plant output.
IT might be able to help. The tools and methods for troubleshooting networks have been around for more than a decade. But the average IT technician has no idea what a PLC is, much less how it works.
If the engineer doesn’t know how to describe “the network problem” in more detailed “IT-speak,” the IT technician may not know how to help.
If plant engineers, control engineers and IT technicians can build an understanding of the network that their devices attach to, troubleshooting logic and good communications will follow. Toward the goal of better understanding, and hopefully better cooperation, communication, collaboration and coordination among plant, control and IT professionals. What follows is a glossary of key network terms and their plant floor translations.
AP client: The most common use of AP in networking describes a wireless access point (802.11 standard). The AP is somewhat comparable to an Ethernet switch in that it provides connectivity to the network for a wireless PC %%MDASSML%% the client. Specifically, the PC uses the wireless protocol to attempt to associate with (attach to) a detected AP.
Attenuation: The loss of signal strength. A signal is said to be attenuated if it has decreased in strength over distance.
Bridge (connection): A bridge often carries traffic between two networks, and often manages that traffic as well.
Cabling: There are three common forms of network cabling: coaxial cable, twisted pair and fiber optic: Twisted pair cable comes in two basic configurations: unshielded (UTP) and shielded (ScTP or STP, depending upon the shielding) Fiber optic cables come in two common types: multimode and singlemode UTP is probably the most common LAN cable system. It’s fairly easy to install, and is the least expensive overall. It terminates in an 8-pin modular plug called an RJ-45 connector. Many industrial systems are converting to the more rugged M12 connector, which requires a different interface.
Client/host: A device communicating on a network. Client, host, station and device are often used interchangeably. Host is commonly used to describe any device (client, server, router, etc.) using the Internet Protocol (OSI Layer 3) communications. Client is often used to describe a device that is communicating with a shared resource, such as a file server.
Client/server: These communications are common, and may indicate whether the particular device is offering a service (server) or asking for the service (client).
Congestion (heavy traffic): describes any situation where more traffic has arrived somewhere in the network than it has the capacity to forward at one time.
Connection: A network connection represents any attachment by any device to a common network. In most cases, what is actually being discussed is the presence of a connecting cable between a PC and an individual switch port: Simple discussions usually focus on whether the connection is electrically complete; that is, if the cable path, as well as the port on the PC and switch are fully operational More advanced discussions may involve a logical attachment between a PC and a server or service, such as connecting to a particular Website. For example, an IT technician may ask, “Could you connect to www.google.com?” That question would assume that the PC has an electrically operational connection to the switch, and would be inquiring about logical connectivity beyond the switch.
Crosstalk: is a form of interference that originates from other pairs of wires in the same cable, or from adjacent cables. There are several kinds of crosstalk: Near-end crosstalk (NEXT or ACR-N) is measured near the signal source. Far-end crosstalk (FEXT, ELFEXT or ACR-F) is measured at the end of the cable away from the signal source. Alien crosstalk is measured from adjacent cables. In testing, a signal is transmitted on an adjacent pair or cable, and the tested pair is monitored to see how much of the transmitted signal can be detected.
Fast Ethernet: describes networks operating at 100 Mbps (within the 802.3 standard). When fast was coined to describe Ethernet systems, the common operating speed was 10 Mbps. Since then, faster systems have been developed, and, today, Ethernet may operate at any speed from 10 Mbps to 10 Gbps with 40 Gbps and 100 Gbps Ethernet soon to be available.
LAN/VLAN: Before switch features became complex and varied, a local area network (LAN) described all of the PCs and other devices connected to hubs, bridges and switches on one port of a router. The router defined the end of what was called a broadcast domain. Everything attached to that router port was within that broadcast domain, network or LAN (depending on which term was appropriate for the discussion). To change router ports was to change broadcast domains. When switch features became more complex, it became possible to logically divide the switch into different broadcast domains. Instead of being physically separated from another broadcast domain by the interconnection of a different set of hubs, bridges and switches attached to a router port, it is now possible to logically separate them via the switch configuration. This logical separation is called a Virtual LAN (VLAN).
Link: is used in two different ways in networking lingo: A link might be the cable path from the PC to the switch A link might be an electrically operational, active connection between a PC and the switch.
Noise: Interference. Noise on a network manifests itself as various forms of interference: Electrical pulses or other disruptive signals passing through the power supply on network devices (such as a PC) and into the network Fro interference, for example, from microwave ovens, radio transmitters, high current-draw equipment such as welders, powerful electric motors, fans, heaters, copiers, coffee makers and fluorescent lights Activity on adjacent network cables and other active pairs within the same network cable.
Port: is used in two different ways in networking lingo: A port is the physical connection or connector, such as the port on a switch or router (e.g., switch port 6) A port is also the software address. For example, a Web browser uses TCP Port 80 for communications.
Protocol: A network protocol is a set of common rules. These rules may describe how to transmit on a cable system or how to form messages to communicate between two computers. In fact, the well-known (seven-layer) OSI Model isolates various activities that have explicit hand-off requirements and expectations between layers. Common protocols used for networking include: Ethernet, which operates at the first and second layer Sip, which operates at the third OSI Layer Top, which operates at the fourth Layer.
Provisioning/certifying/characterizing/pre-testing (commissioning, base lining, benchmarking): When a new server or service comes online, provisioning includes specifying, configuring and testing its delivery (a plant engineer might call this commissioning or base lining). When installing any new system or capability, someone has to verify that the new installation has been certified in comparison to the standards. Ensure that the installer (contractor) has (in IT-speak) characterized it (or in plant speak, taken baseline data readings for the new system’s cabling, connections, etc.) Both IT and plant engineering must have benchmarks against which to compare operational values during troubleshooting.
Switch: In IT-speak, a switch is any multi-port bridging device. Today, switches include highly complex and configurable bridges, routers, firewalls and servers. Plant personnel should not be thinking SPST, DPDT, etc. in this context.
TCP/IP: Is the popular networking protocols used for Internet communications. TCP and IP actually refer to two different and distinct protocols: Transmission Control Protocol (TCP) and Internet Protocol (IP): At OSI Layer 3, the dominant protocol today is the Internet Protocol, which is used by routers to forward messages around the Internet to the intended destination At OSI Layer 4, the protocol TCP is only one of several common protocols. Another common OSI Layer 4 protocol is UDP. TCP is a guaranteed-delivery protocol used for operations such as file transfer, while UDP is a “best effort” protocol for when the extra overhead required by TCP to acknowledge each data packet is not necessary. UDP supports operations such as Internet radio and streaming video. FOUNDATION Field bus HSE and Prefabs are based on both UDP and TCP; traditional Field bus and CAN are based on UDP; and Ethernet/IP is based on TCP/IP.
Rogue device: most often applies to a wireless device (802.11 standard). In this context, it is as an unauthorized presence on the wireless network. It might mean one of three things: An unauthorized access point offering connectivity to the network A previously unknown network device, for example, a new Pectin a security context, it might include someone close enough to the premises where the network is deployed that they can attempt to gain unauthorized access. Know what? It professionals need not worry that plant and control engineers may be configuring enterprise software for the finance department. Control engineers need not worry that IT technicians will be swapping I/O modules in the PLC racks. But armed with the understanding of some of the language used by IT and plant floor professionals, communication, cooperation and collaboration can be a much easier process. A technician certifies connectivity and performance for both copper and fiber optic links in an industrial Ethernet network. A technician tests for common device connectivity issues on industrial Ethernet links with up to 10, 100 and gigabit speeds, including cables running power over Ethernet (Poe). A technician uses a scope-type network analyzer to test and analyze traffic on copper, fiber or wireless industrial Ethernet segments. A technician troubleshoots and qualifies cabling on industrial Ethernet networks. The tool shows why existing cabling cannot support the network’s bandwidth requirement. A technician checks electrical signal levels, speed, transition times and distortion on industrial buses and networks.
Neal Allen is a level 3-escalation engineer at the Technical Assistance Center for Fluke Networks. He has worked for Fluke since 1989, and has been in the Fluke Networks networking products group since 1992. Special focus has been placed on technical marketing, product development, beta testing and special projects. In 2002 the Technical Assistance Center was restructured, and in the capacity of a level 3 escalation engineer, Allen has dealt with many of the issues surrounding analysis of the higher OSI layers, while maintaining awareness of the lower layers and how they affect monitoring and troubleshooting.