Ethernet Gives New a Big Advantage Stanley Liu, Moxa Product Manager (stanley.liu@moxa.com) The main purpose of remote monitoring and alarm systems which are used for applications such as security, restricted access, power substations, and remote site management is to provide vital information in real time, 24 hours a day, 7 days a week. The current expectation is that a remote monitoring and alarm system will provide detailed warning messages in a human-readable format. Engineers who monitor the system should receive all important alerts, but without receiving a lot of nuisance alarms. Maintaining an efficient and secure system is equally important. A new remote monitoring and alarm architecture uses the bi-directional communication advantage of Ethernet to provide engineers with an efficient and cost-effective solution. The Most Common Remote Monitoring and Alarm Systems System integrators have traditionally used one of two different solutions to build a remote monitoring and alarm system. PLCs play an essential role in the first solution, whereas the second solution is based on PC technology. Common solution 1 is PLC-based The overall structure of the PLC-based solution has three levels. The first level consists of PLCs connected to sensors and other equipment, the second level is a proprietary PLC network, and the third level consists of networked PCs. For this type of solution, the host computers are required to poll the Released on April 15, 2008 Copyright 2008 Moxa Inc. All rights reserved. Moxa manufactures one of the world s leading brands of device networking solutions. Products include industrial embedded computers, industrial Ethernet switches, serial device servers, multiport serial cards, embedded device servers, and remote I/O products. Our products are key components of many networking applications, including industrial automation, manufacturing, POS, and medical treatment facilities. How to contact Moxa Tel: 1-714-528-6777 Fax: 1-714-528-6778 Web: www.moxa.com Email: info@moxa.com This document was produced by the Moxa Technical Writing Center (TWC). Please send your comments or suggestions about this or other Moxa documents to twc@moxa.com.
PLC network to collect data from the sensors and devices connected to the PLCs. One advantage of the PLC-based solution is the flexibility that comes from being able to connect to a variety of sensors. The disadvantage, however, is that most PLCs use proprietary protocols, which means that additional devices, such as PCs, must be purchased to convert between the proprietary and Ethernet protocols. Another issue is compatibility, particularly when security cameras are involved. Figure 1: PLC-based Solution Common solution 2 is PC-based In order to reduce costs, a PC-based remote monitoring and alarm solution was introduced. The advantage of this solution is that it eliminates the compatibility issue by relying on the open standard TCP/IP protocol used on Ethernet networks. One disadvantage, however, is that users must purchase specialized monitoring software, which must be upgraded each time the system is scaled up. For large-scale systems an even more crucial problem is the time-lag introduced by the polling done by host PCs. Since the PCs must poll remote I/Os periodically to Copyright 2008 Moxa Inc. Page 2 of 7
obtain data from sensors and devices, as the scale of the system increases (some large systems contain thousands of IOs), the network bandwidth devoted to polling increases proportionally. Figure 2: PC-based Ethernet I/O Solution Pushing vs. Pulling over Ethernet One of the most important features of Ethernet communication is that it is bi-directional. In other words, any device on an Ethernet network has the right to contact any other device. This is great news, since we can take advantage of this bi-directional feature to create a remote monitoring and alarm system that uses push instead of pull. Iinstead of requiring network hosts to pull data up from the sensors and other devices periodically, we enable all such devices to push their status up to the network hosts. The push concept is particularly advantageous for alarm systems, since the status of the devices will only be reported (i.e., pushed ) when an exception occurs. Copyright 2008 Moxa Inc. Page 3 of 7
The Newest The newest remote monitoring and alarm solution uses Ethernet s push concept. Although data can either be pulled or pushed, the greatest advantage comes from allowing devices to push their status to network hosts over the Ethernet network. In this case, the PC hosts do not need to expend a lot of effort retrieving sensor status, since all they need to do is wait until the sensors send the status themselves. Figure 3: Active Ethernet I/O Architecture This new Active Ethernet I/O architecture has the following useful features: Active event-driven messaging uses less Ethernet bandwidth In addition to receiving messages from I/O sensors reporting an exception, hosts can also be notified of user-defined events. Since event-driven messaging does not use polling, it uses far less Ethernet bandwidth than other solutions. This is an extremely important benefit for Copyright 2008 Moxa Inc. Page 4 of 7
monitoring applications, since such systems are set up to report events that occur only rarely. Messages can be sent using any of several methods, including TCP socket, SNTP, email, and SNMP. SNMP with I/O status is suitable for IT users SNMP is a popular remote management tool in the IT industry, particularly since it can be used in conjunction with database systems such as ERP and CIM via SNMP. This is an important feature for IT engineers when it comes time to upgrade existing systems. Real-time I/O time stamp without time delay For most monitoring systems, a time stamp is attached to each event by the controller or PC host. The time stamp lets users know the time lag between when the event occurred, and when the report was received. Real-time time stamps are useful for identifying the sequence of events, and make it easier to maintain the entire system. Front-end intelligent local logic for distributed systems Remote monitoring and alarm applications often involve monitoring sites distributed over a wide area. One problem with traditional remote monitoring and control systems is that all the brains for the system are located in the central control room. If the control room loses contact with the remote devices, there is no way for the hosts in the control room to receive alerts. Front-end intelligence uses a different approach. By placing some of the intelligence near the sensors and devices, the system can make use of local logic to keep the local alarm system working even if the network fails. In addition, combining inputs and outputs in the same local module ensures greater reliability. Copyright 2008 Moxa Inc. Page 5 of 7
Conclusion Ethernet technology has the unique advantage of bi-directional communication, which has given rise in the IO industry to the so-called push and pull technologies. Active Ethernet I/O uses push technology to create a new type of remote monitoring and alarm system, which is particularly well-suited for applications that rarely experience exceptions. This new architecture provides the following benefits: Open standard TCP/IP and Ethernet Uses less bandwidth for bandwidth-critical applications Front-end intelligence reduces host loading 24/7 unmanned monitoring with multiple notification types Human-readable, detailed alarm descriptions Filter out most nuisance alarms Expansion capability for future scale-ups Active Ethernet I/O is an appropriate solution for a broad range of I/O applications. The following list shows just some of the many applications that can benefit from using this new technology: Unmanned Site Monitoring Transportation Power/Energy Telecom Environmental Monitoring Environmental Applications Water and Waste Water Management Alarm Systems Security/Surveillance Factory Automation Building Automation Copyright 2008 Moxa Inc. Page 6 of 7
Disclaimer This document is provided for information purposes only, and the contents hereof are subject to change without notice. This document is not warranted to be error-free, nor subject to any other warranties or conditions, whether expressed orally or implied by law, including implied warranties and conditions of merchantability, or fitness for a particular purpose. We specifically disclaim any liability with respect to this document and no contractual obligations are formed either directly or indirectly by this document. This document may not be reproduced or transmitted in any form for any purpose, without our prior written permission. Copyright 2008 Moxa Inc. Page 7 of 7