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Internet-Based The potential of Internet-based systems is tremendous, and the technology is available today. Only nagging questions concerning security and reliability are holding these products back. Once the Internet
Frederick A. Putnam, Wouldn't it be great if you could access sensor readings remotely via the Internet? This wish was expressed almost as soon as the Internet was invented, and it was first realized way back in the 1970s. Today, Internet-based sensing is a mature, commercially available technology, though it's application has been limited in many areas. Early Uses of the Internet
In the 1970s, caffeine-hungry programmers in Carnegie-Mellon's Computer Science Department first used the Internet to monitor the supply of Coke in the department's vending machine. This technical tour-de-force was imitated by others and was followed by many other early homebrew systems just to show what could be done. Some of these--including hot tubs, coffee machines, and model trains--are still available. Links to them can be found on a Web page called Interesting Devices Connected to the Net. Long before the Internet, people accessed computers via remote RS-232 terminals connected by modems and phone lines (I personally used these extensively as a student at Dartmouth College, beginning in 1965). Today, the equivalent of this kind of access is provided by all kinds of remote console hardware and software, including software products like Lap Link and PC Anywhere. These now work over the Internet and let you see the display and take over the keyboard of a remote PC. For some applications, these products provide remote access to sensor data, but their use is limited to cases where it's all right to give the remote user total access to the PC. For some, the phrase remote sensing refers primarily to the use of satellite imaging techniques to provide information on geology, weather, and other fields. This is a well developed technology, and the Web is a great medium for making the resulting images available for viewing. To see the extensive number of sites on this subject, type remote sensing into any Web search engine. What is Real Time in Internet Sensing? It's important to keep in mind that real time means different things to different people. Each application has its own time scale. For remote sensing, one day is often referred to as real time. For the direct sensor data viewing applications described below, real-time sensor displays can be as fast as the network in use. For the Internet, this can easily be 10 Hz or more. Direct Sensor Data Viewing from Web Browsers
State-of-the-art methods of Internet-based sensing and control use Web browsers to deliver direct sensor data viewing. Here, the viewer, or client, is most often a PC with an Internet connection. The sensors are wired to one or more server computers, which may be PCs, instruments, or even microprocessors integrated into the sensor (see Figure 1). The key information that allows the server and client to send and receive information is their Internet addresses. These are analogous to phone numbers for telephone communication. They can usually be expressed in two equivalent forms: the host name and the TCP/IP address. The easiest of these to use is the host name. This is an alphanumeric string of characters, which makes it a lot easier to remember than the TCP/IP address. For example, the host name of our company's sensor data server is ltserver.labtech.com. The last part of this string, labtech.com, identifies the domain name of our company on the Internet. The TCP/IP address corresponding to this host name is 209.61 The Web Server Approach Hewlett-Packard pioneered an approach in which a small Web server is embedded in a microprocessor that is connected to a sensor or sensors. Periodically or whenever there is new data, the server creates a Web page containing sensor readings. When a client requests the Web page, it's sent out over the Internet to the client, who can see the data values (see Screen 1). This design is now used in many products. But this approach is limited in flexibility and efficiency because the Web server that constructs the Web page has limited processing power and little ROM. Given these limitations, the Web page layouts are difficult to change. And while the pages are fine for viewing data, they are not well suited if the client wishes to parse the data values and do additional processing or local data storage. Finally, this approach is inefficient because it requires an entire Web page to be sent every time the data are updated, so it's sending much more data than necessary. These drawbacks are overcome by the application server approach. The Application Server
The most efficient and versatile approach to direct sensor data viewing is a system in which you separate the serving of the sensor data from the serving of the Web page. Thus, you are working with two separate data streams. The sensor microprocessors send only the sensor data across the Internet; they don't serve any Web pages. The microprocessors aren't Web servers, rather they are specialized application servers--sensor data servers. The Web page is served separately from a corporate Web server or even from the local hard disk in the client PC. This is good because the Web pages will be served from the same server that all the other nonsensor corporate Web pages are served from. This approach uses a Web page plug-in to receive and render sensor data (see Screen 2). The plug-in is a small, simple software component that runs on the client PC when a Web page loads the component. There are several ways of implementing plug-ins: ActiveX controls, Netscape plug-ins, and Java applets. Any one of these can be used to retrieve sensor data from the server, render the data in a Web page, and provide any processing or storage that might be necessary. This approach was pioneered by Labtech and announced in October 1995. The technology is now commercially available in NetTrender and is also bundled with the Labtech Notebookpro and Labtech Control products. The Future Looking into the future, you can see great potential in Internet-based sensing and control, especially with handheld devices like Palm Pilot and the recently announced Handspring Visor. You'll also begin to see closed-loop control over the Internet. The technology for control is here today, and research and pilot programs are under way. The main reason it isn't widely used today is security and reliability, but these issues will gradually be solved as the Internet becomes more hardened and mission-critical capable. The developers of these ultra-reliable extensions to the Internet will be the new e-commerce industry.
Frederick A. Putnam, Ph.D., is President and Founder of Laboratory Technologies Corp. (Labtech), Two Dundee Park, Ste. B09, Andover, MA 01810; 978-470-0099, x-231, fax 978-470-3338, fred.putnam@labtech.com
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