The File - Nov 16, 2008 - (Page 6)

In Focus | Data acquisition Working with IT for networked DAQ By Charlie Stiernberg Product Marketing Manager Remote Data Acquisition National Instruments Corp. Have you ever heard of an IT professional who measures strain gauges or an automotive engineer who manages remote authentication dial-in user service (RADIUS) servers? The line between these once mutually exclusive roles is beginning to blur as PC-based technologies familiar to the information technology (IT) sector find their way into measurement applications. This is more true today than ever with advances in networking and wireless technology. Ethernet and IEEE 802.11 (Wi-Fi) have become the de facto standards for enterprise networking, and their performance, reliability and security have matured to make these technologies viable for data acquisition (DAQ) applications. However, most network infrastructure is typically managed by an IT department, and most IT departments have different priorities than scientists or engineers. The key to creating synergy between IT and engineering groups is communication, and to communicate ef fectively, you must understand the IT vernacular. The following guide provides an overview of the key components you should consider when working with your IT department to add Ethernet or wireless measurements to your data acquisition application. The distribution of your measurements is most effectively realised when you use the existing network infrastructure, such as existing enterprise networks. The typical corporate network topology is similar to that shown in figure 1. One of the most common points of confusion in networking is the difference between hubs, switches and routers. All three devices share the same physical appearance (a box with RJ45 jacks on the front or back), but their internal functions are quite different, as explained below: • Hub—An Ethernet hub is nothing more than a repeater. It collects incoming traffic (TCP/IP packets) from each port and repeats it to all other ports, whether the traffic is addressed to those ports or not. • Switch—An Ethernet switch is a more intelligent device than a hub. It inspects each incoming TCP/IP packet before sending it to an appropriate destination, based on its media access control (MAC) address. This reduces packet collisions and unnecessary traffic on the local area network (LAN). Figure 1: The typical IT network consists of clients, switches and routers. also provide a firewall to limit the traffic passing into and out of the LAN. Having all of your devices physically connected is only the first step in designing a network; all devices must also have an address, so they can communicate with each other. When you plug an Ethernet data acquisition device into a switch on a corporate network, it first attempts to obtain an IP address from a dynamic host configuration protocol (DHCP) server. A DHCP server maintains a pool of available IP addresses for clients attached to the network. These addresses are “dynamic,” meaning that they have an expiration date and may change, depending on network administration. If no DHCP ser ver exists or the Ethernet DAQ device is unable to communicate with it, the DAQ device can use a link-local IP address (169.254.1.0 – 169.254.254.255) to establish communication within a LAN. You or your IT department may wish to assign the Ethernet data acquisition device a “static” IP address instead, which you must enter manually. In addition to the IP address, all IP-based network devices have “Subnet Mask,” “Gateway,” and “DNS Server” settings. If your corporate network has a DHCP server, these fields populate Discuss Going for IT? If the next liberating step for measurement is DAQ via wireless network, should engineers take IT training? Would you? Ethernet networking Ethernet is as ubiquitous in the PC industry today as USB. It enjoys such wide acceptance because it is easy to understand, deploy, manage, and maintain. When you plug in an Ethernet cable, it just works. For data acquisition applications, Ethernet offers an extended range of up to 100 metres per segment for highly distributed or remote measurement applications. • Router—Routers are designed to join multiple area networks together. A router serves as an intermediate destination for packets travelling between LANs in a corporate network or between a LAN and the Internet. In a small office or home office (SOHO) network, you can use routers to share one broadband Internet connection between multiple clients. Most routers automatically. If not, you must work with your IT department to fill them in appropriately. Following is a brief explanation of these settings: • Subnet Mask—A subnet is a logical segmentation of a larger network, and is important for making the amount of traffic in a LAN manageable. In most networks, a subnet is defined as all the clients and switches connected to a router. The subnet mask splits an IP address into two parts: the network address and the host address. All clients in the same subnet share the same network address, but have a unique host address. • Gateway—A gateway is also typically associated with a router and serves as a connection point to networks outside the LAN. When a node (client, switch or router) on a LAN has to send a packet outside the LAN, it forwards the packet to the gateway node. The gateway either connects directly to the destination network or continues to pass the packet to the next gateway. • DNS Server—Domain name system (DNS) servers translate user-friendly domain names (or host names) to IP addresses. continued on page 10 EE Times-India | November 16-30, 2008 | www.eetindia.com http://www.eetindia.co.in/SEARCH/SUMMARY/technical-articles/Ethernet.HTM?ClickFromNewsletter_081116 http://www.eetindia.co.in/SEARCH/SUMMARY/technical-articles/MAC.HTM?ClickFromNewsletter_081116 http://forum.eetindia.co.in/FORUM_POST_1000039249_1200094009_0.HTM?ClickFromNewsletter_20081116 http://forum.eetindia.co.in/FORUM_POST_1000039249_1200094009_0.HTM?ClickFromNewsletter_20081116 http://www.eetindia.com/STATIC/REDIRECT/Newsletter_081116_EETI02.htm?ClickFromNewsletter_081116

Table of Contents for the Digital Edition of The File - Nov 16, 2008

EETimes India - November 16, 2008
Contents
Farnell
Embedded System Eases Rail Maintenance
National Semiconductor
Working With IT for Networked DAQ
Digital Telemetry Advances Torque Measurement
Events

The File - Nov 16, 2008