In addition to tuning control loops or programming programmable logic controllers, engineers must become proficient in network management and troubleshooting. Ethernet has become the de facto networking standard on the factory floor.A key technology for engineers to know as they implement their networks is Simple Network Management Protocol (SNMP). Knowing and using this technology, engineers can avoid some problems in the first place, and then know the questions to ask information technology (IT) people if other problems do arise. Fortunately, some automation companies are working on SNMP solutions designed specifically for use by engineers, as a way to help the process.“SNMP forms part of the Internet Protocol (IP) suite as defined by the Internet Engineering Task Force (IETF). SNMP is used in network management systems to monitor network-attached devices for conditions that warrant administrative attention. It consists of a set of standards for network management, including an Application Layer protocol, a database schema and a set of data objects. SNMP exposes management data in the form of variables on the managed systems, which describe the system configuration. These variables can then be queried (and sometimes set) by managing applications,” states the entry on Wikipedia.The Wikipedia entry notes that SNMP agents expose management data on the managed systems that can then be retrieved by the managing system. Management systems can also send configuration updates or controlling requests. These variables, organized in hierarchies, are described by Management Information Bases (MIBs). This extensible design describes the structure of the management data of a device subsystem. MIBs use a hierarchical namespace containing object identifiers (OIDs) that identify a variable that can be read or set via SNMP.The three key components of an SNMP-managed network include managed devices, agents and network management systems (NMSs). Again, according to the Wikipedia entry, “A managed device is a network node that contains an SNMP agent and that resides on a managed network. Managed devices collect and store management information and make this information available to NMSs using SNMP. Managed devices, sometimes called network elements, can be any type of device, including, but not limited to, routers and access servers, switches and bridges, hubs, IP telephones, computer hosts or printers.” An agent is a software module that resides in a managed device. A network management system executes applications that monitor and control managed devices.
Tools available
Kepware Technologies Inc., of Portland, Maine, offers a network monitor for SNMP designed for automation engineers at a reduced cost and footprint over enterprise-level management systems. The “iSNMP” monitors SNMP-compliant devices and also monitors the health of non-managed devices with a “ping” driver that regularly tests them with a transmission control protocol/Internet protocol (TCP/IP) ping. It also can publish data via SNMP so that IT professionals can monitor the industrial network with their tools. It communicates with human-machine interface systems via OPC (an open communications protocol).Another industrial network management tool comes from Network Vision Inc., of Newburyport, Mass. IntraVue is a network visualization tool designed to give control engineers the ability to identify problems on the network by automatically mapping all IP devices in a network and showing their communication status on a single graphical display. In some cases, this helps control engineers aid the IT department in correcting a problem quickly. In many cases, though, it enables plant floor personnel to correct the problem themselves. That’s because, according to Network Vision President Mark Fondl, most network disruptions are caused by the failure of the connected devices operating in the harsh plant floor environment, not by software.Gary Mintchell,
[email protected], is Automation World’s Editor in Chief.
