Just as users are becoming familiar with LXI and its benefits, manufacturers are finding out how to efficiently add LXI capabilities to instruments and build in features users will find attractive and easy to use. So, what are the major product trends you can expect to see in the next months?

In speaking with LXI suppliers, I' ve found them universally very enthusiastic. They say that the move to LXI is simply so logical and obvious that the spec' s success is inevitable, and to be a player in the future, they have to be on-board. As a result, they' ve started making significant investments in terms of time and funding, and we' re seeing their first fruits. But product development is as yet embryonic.

It' s important to recognize that LXI is evolutionary rather than revolutionary. That is, it doesn' t add any fantastic new functions. Everything you could do before you can do now— but in some cases much more easily.

By itself, " LXI doesn' t change the world. There are no earth-shaking measurement capabilities with LXI today," commented Mike Kawasaki, senior manager, Next Generation of Tests Initiative at Agilent Technologies. " There is huge potential, but it will take time. Suppliers need to learn how to best integrate these capabilities into their instruments, and users have a learning curve to climb."

Will LXI take over as the single dominant instrumentation standard? Most people think not. Modular schemes such as PXI and VXI still will have a place. But when it comes to connecting discrete instruments together, that' s where LXI shines.

According to Chuck Cimino, a marketing director at Keithley Instruments, " We envision GPIB as falling by the wayside. USB will be viable for single instruments, and LXI will dominate for connecting discrete instruments. In the transition period, we will likely offer all three, perhaps with GPIB as an option."

From the viewpoint of Peter Allen, product marketing manager at Xantrex/Elgar, " LXI is the next logical thing, and Class C is the next evolutionary step after GPIB." For a summary of classes, see the sidebar.

Manufacturers as well as users are in a transition period. For instance, Kepco is upgrading its existing power supplies and making LXI an option. To make room in the supplies, they remove the RS-232 interface. In new designs, the company hopes that LXI becomes standard with GPIB as an option.

In the meantime, customers are not forced to build complete LXI systems from scratch; their test systems can evolve. They can build around a LAN backbone, but it is key that they can reuse existing test-system components while moving to LXI.

It' s difficult to pin down how many people are actually using it because of the lack of LXI-only instruments. LXI is in the mix, but it' s not yet a primary driver for people buying instruments.

To get some rough indication of where the market is going, consider power supplies from Xantrex/Elgar. For the moment, LXI is available only as an option. Today, 10% of the units the company ships go out with the LXI option, and the number is growing steadily.

Already there' s a wide selection of LXI-compatible products, and with them, you should be able to put together systems that meet a wide range of requirements. Agilent, a co-founder of the LXI Consortium and presently offering the widest selection of certified products, has tried to include at least one LXI instrument from each of its major product lines.

In general, though, only a few LXI products implement the spec in its full form. That is, most conform to Class C specs as opposed to Class B or A.

This situation is changing with a number of product introductions at AUTOTESTCON this month. Besides an extensive demo in the LXI Consortium booth, a number of member companies will demo LXI in their own booths. One interesting demo will be based on a wireless LAN.

What' s Getting Customers Excited?
So what aspects of LXI are actual users getting excited about? Vendors report that initially it' s the LAN interface. Second, they like avoiding investing lots of money in cables and controllers. Third come the software issues such as the capability to program with standard drivers and operate instruments with web-page interfaces. Finally, there are the life-cycle issues.

Today, explained Agilent' s Mr. Kawasaki, users sometimes actually hate new products because when it' s time to replace an instrument they have to reconfigure their systems. With LXI, they can purchase a new box and take advantage of its form factor and functions, yet it will be compatible with the existing system.

LXI also is very attractive for building distributed systems, even in an unconventional sense. Engineers like to work from many locations, whether in the office, at home, or in a coffee shop. With LXI, they can access instruments from anywhere, using built-in web pages to run tests and check results.

For instance, Jon Semancik, formerly corporate marketing and business development manager at VXI Technology, reported that Boeing uses a number of the company' s EX1629 Strain-Gage Boxes, a model built to be LXI compliant but not yet officially certified, to test the wings of its 787 Dreamliner. Similarly, Jochen Wolle, a software development manager at Rohde & Schwarz, explained that for EMC applications people want control of a test receiver inside a shielded chamber. Rather than route standard cables into this protected area, the LAN connection can be based on fiber optics.

For power supplies, noted Xantrex/Elgar' s Mr. Allen, the LAN approach can be very attractive. Many power-supply applications require sense leads on the DUT to help compensate for voltage drops in the cables, and these leads usually are designed for a couple of volts.

But, what if a missile system is located at a distance on the launch pad, resulting in large voltage drops that can be difficult to deal with? Although the test engineer must be far away, the power supply need not be. With LXI, you can simply put a LAN connection close to the missile and not worry about the control computer being too close. Similarly, engineers working in a wafer fab wouldn' t have to dress in a clean-room suit to debug a test setup.

LXI has other attractive features in specific industries. Physical size can be an issue, particularly when working with microwave signals or in switching high currents such as in the automobile industry, reported Bob Stasonis, sales and marketing manager at Pickering Interfaces.

Some microwave relays are so large that only two or three can fit on a PXI card, and a system will need multiple cards and even multiple chassis. That requires lots of plumbing, which, in turn, affects insertion loss and VSWR. With LXI, the company can offer better specs and use larger, lower-cost relays. In this way, users have switching that is inexpensive to scale up.

The Integrated Web Page
The first round of LXI instruments has been dominated by Class C units that are upgrades of existing designs. Some vendors previously had Ethernet-based instruments, even some with built-in web pages. But they weren't standardized, so interconnecting them could require significant time.

But even at this lowest level of compliance, the LXI spec leaves considerable room for interpretation and enhancements. As a result, manufacturers are taking different approaches to how they deal with it. Some implement the very minimum to get a unit certified; others add special features.

   

Actual Front Panel (top) and Replica Built-In Web Page (bottom) of Keithley’s Model 2810 RF Signal Analyzer

Even so, Class C units have much to offer. One core feature is the integrated web page. LXI has fairly minimal requirements in this regard, and here manufacturers can add interesting features.

With Keithley' s Model 2810 Signal Analyzer, users can view a remote version of the analyzer' s front panel on a PC. The web page closely resembles the instrument' s actual front panel and display in what Keithley terms a lively remote interface. Also, multiple users can view the instrument' s front panel simultaneously.

Perhaps an engineer in a lab wants to ask colleagues elsewhere for their opinion of certain test results. In an educational setting, an instructor can set up the instrument and, instead of the students crowding around it trying to get a peek at the settings and results on the display, they all can have the instrument display appear on their PCs.

The web page also will have an impact on how users program instruments. " With that web interface, we think it likely will be possible to eliminate ancillary software for many sequential or analytical applications," added Keithley' s Mr. Cimino. For complex test applications, users will still want a test executive. But for simple sequential tasks, the web page gives customers alternatives to big software applications.

For its LXI switching networks, Pickering wrote a Java applet that allows users to set switches at random. Some of their customers find that they don' t have to write any code; they just manipulate the switches on the web page.

Similarly, Agilent points to how time can be saved when setting up its Model 34980 Switch. On a PC screen, users can visually click through a series of tasks. The software contains a logging capability so that you first click through the tasks, then ask for the commands to generate code from this listing capability.

The situation is somewhat different with power supplies, and Kepco still is tinkering with their web-page design. For now, that page basically lets you set all power supply parameters. The company' s plan with its bipolar supplies, though, is to implement a list command to program waveforms on a point-by-point basis in a sort of basic function generator.

EX2500 LXI-VXI Gigabit Ethernet Slot-0 Interface From VXI Technology

Interestingly, one thing that Kepco discovered is that more than one person can try to control the same power supply at the same time, which would lead to the instrument locking up. As a result, they have implemented a password feature whereby only one person at a time can take control of the instrument.

Class C is perfectly adequate for many power supply applications. Rise times are orders of magnitude larger than the difference between the control signals of GPIB vs. LXI so precise triggering, as in Class B and A designs, isn' t mandatory. Further, power supply control is not an application with a large data package so control commands can move quickly across the net.

Even if there' s lots of bus traffic, a control signal has a delay of only a few milliseconds. According to Mr. Stasonis from Pickering, " Some customers are afraid of sending control signals over the LAN. But by setting up the network properly, we can alleviate these fears."

Class B: Triggers Over the Ethernet
Those who do need precise triggering will start investigating doing so over the Ethernet. Here LXI works with IEEE 1588, a standard that defines clock synchronization over a LAN.

Because early prototypes of this scheme were developed by Agilent, it' s no surprise that the company currently has the largest number of instruments with this capability. Until recently, there have been no pure Class B instruments available; they' ve either been Class C (with no LXI triggering) or Class A (with both LAN-based and hardwired triggering).

There is great potential with this little understood technology. The trick is in implementing it in a particular instrument, and there is a significant learning curve for both users and manufacturers. Some vendors even say that adding 1588 is the most expensive and toughest part of this business.

Rack of Class A Synthetic Instruments From Agilent Technologies

Even so, a growing number of products with IEEE 1588 capabilities will appear shortly. You can get a first-hand look at some at two separate demos at AUTOTESTCON this month. The LXI Consortium is presenting a Class B demo that involves multiple vendors including National Instruments, Rohde & Schwarz, and Agilent. Agilent is showing the power of timing synchronization through a new trigger box and the capability of its MXA Spectrum Analyzer and MXG Signal Generator to communicate through peer-to-peer capabilities.

Class B adds some unique features such as peer-to-peer communications without sending signals over a wired bus. It would be useful, for instance, to have an RF signal generator send a stimulus and then notify a spectrum analyzer directly to take a measurement without having to involve a central controller.

A small program inside each box could send signals back and forth as the two instruments step through a series of frequencies. Users could download a list of frequencies, have each instrument run on its own time, and tell the central controller when that task is done. This approach would take traffic off the bus and speed up system-wide communications.

Class A: The Wired Trigger Bus
Currently, the only Class A products are available from Agilent and VXI Technology. The Class A wired trigger bus (WTB) plays a large role in letting engineers integrate LXI into existing test setups and makes LXI compatible with legacy hardware while allowing people to ease into these new technologies. This is part of the philosophy behind VXI Technology' s EX2500, an LXI-VXI Gigabit Ethernet Slot-0 Interface.

Rohde & Schwarz FSL Spectrum Analyzer With Class C Plus Capability

For the moment, all of Agilent' s Class A products can be used to build synthetic instruments. These modules, building blocks rather than complete traditional instruments, include a digitizer, a downconverter, a waveform generator, and an upconverter.

One distinguishing feature they all share is the lack of a front panel: Everything is controlled via software. By combining these modules in various ways, users can emulate traditional instruments or create specialized instruments. The reusability of modules in different measurement scenarios reduces the total lifetime costs of a test system by extending its longevity and provides obsolescence protection.

Much is said about the cost of GPIB cables, and while LAN cables are inexpensive, WTB cables aren' t throwaways. One of the few suppliers is VXI Technology, whose Class A triggering cables cost from $158 to $475 in distances from 0.5 m to 20 m. The connectors are expensive because they are 25-way microD connectors with shielding.

Class C + WTB = Class C Plus
While Class A instruments must include both the WTB and IEEE 1588 triggering, several vendors have developed Class C instruments that add the WTB but not IEEE 1588. They' re more than Class C but don' t qualify as Class A, so some vendors refer to them informally as Class C Plus instruments.

One such supplier is Rohde & Schwarz, whose FSL Spectrum Analyzer has been certified with its LXI hardware trigger. It has a slot that accepts an option card populated with an FPGA that implements the routing of the trigger signals across the WTB.

In addition, there is room on this FPGA to accommodate hardware support for the IEEE 1588 clock synchronization and time-based triggering. With these counter registers for clock implementation and hardware comparison of timestamps, Mr. Wolle said the IEEE 1588 implementation achieves accuracy of between 10 to 20 µs where a pure software scheme would work at 100 to 150 µs.

C&H Technologies is adding the WTB to the EM405-8, an M module carrier already approved as a Class C instrument, to make it another Class C Plus box. Interestingly, the EM405-8 is not a product upgraded to LXI. The company planned to include Ethernet capability and designed it from the ground up for Class C operation.

Reference
1. Dewey, M., " LXI Instrument Classes," LXI ConneXion, January 2006, pp. 8-11.

About the Author
Paul G. Schreier is a technical journalist and marketing consultant working in Zurich, Switzerland. He was the founding editor of Personal Engineering & Instrumentation News, served as chief editor of EDN Magazine, and has since written articles in countless technical magazines. He earned a B.S.E.E. and a B.A. in humanities from the University of Notre Dame and an M.S. in engineering management from Northeastern University. e-mail: paul@pspr.biz

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LXI Makes Smart Instruments Possible

By Paul F. Franklin, Keithley Instruments

Smart instruments that do more work and relieve the burden on test system designers are becoming more available. These instruments incorporate a number of advanced functions, including the capability to make complex measurements and control timing and sequencing.

Smart instruments also can perform highly sophisticated data analysis that helps transform raw data into useful information. These and other capabilities greatly improve the performance of test systems while simplifying setup, debugging, and troubleshooting.

However, while instruments are becoming smarter, none have reached the level of intelligence most users would like. One factor limiting the development of smart instruments is cost. Defining, designing, and producing truly smart instruments increase development cost, time to market, and product cost.

As a result, instrument makers must strike a balance between the market' s demand for less expensive but more intelligent products and the need to bring products to market faster. For smart instruments to truly make an impact, instrument makers must demonstrate how they can reduce the total cost of test before users will be willing to pay more.

Technical considerations also limit the development of smart instruments. Instruments typically must interface with other equipment and software as part of a complete test system. Because few test systems are configured exclusively with one vendor' s products, the limitations associated with other components and the interfaces may restrict the overall level of possible improvement.

Major instrument manufacturers recognized that current technology and standards limited their capability to provide smarter instruments at lower total cost. This realization played a major role in the formation of the LXI (LAN eXtensions for Instrumentation) Consortium. LXI-compliant instruments provide a number of capabilities that improve the prospects for the development and deployment of smart instruments.

The Power of LXI
The key features of LXI that make smart instruments possible include the following:

●  A LAN interface featuring a defined standard network configuration, a Web page for network configuration, and a discovery mechanism for locating LXI devices on a network.
●  A Web interface consisting of a set of standard Web pages that provides information about the instrument, a standard way to configure the LAN interface, and other features.
●  Timing and synchronization based on IEEE 1588 that synchronizes real-time clocks in each device and can be used to timestamp data or initiate time-based triggers.
●  An IVI-compliant instrument driver.
●  Peer-to-peer messaging from one LXI device to another that implements LAN triggering and supports a short data payload.
●  A uniform trigger model and event structure.

These features provide a powerful toolbox for vendors developing smarter instruments, especially when combined with test-script programming that will be available in next-generation instruments.

Smart Instruments at the Interface
Besides being a key factor in making smart instruments possible, LAN connectivity can simplify maintenance and support. For example, the LAN interface provides centralized maintenance monitoring in which the calibration and maintenance status of all instruments can be monitored and tracked from a remote location. This capability also allows remote asset tracking of instruments.

Firmware upgrades also are easier because they can be installed over the network. In addition, in-house and vendor technical support personnel can diagnose problems remotely over the LAN, saving the time and expense of sending a technician to the instrument location. Finally, users can share and administer licenses for advanced features over the network. All these features can reduce support, maintenance costs, and downtime.

The basic Web pages recommended by the LXI specification make instruments easier to integrate and use, but they do not fully demonstrate the potential of a full-featured Web interface. Web technologies such as Asynchronous JavaScript and XML (AJAX) and Java applets can provide a rich, responsive, and easy-to-use Web interface with relatively modest memory and processing power requirements. Potential features include full instrument configuration and control, tabular or graphic data display, extensive user help, and wizard-style guidance for common tasks.

An enhanced Web interface can provide several benefits, including the following:
●  Web pages that can be viewed on any browser from a remote computer.
●  The ability to operate an instrument from anywhere in the world.
●  No requirement to install software on a remote computer.
●  No software version conflict issues because the Web interface is always the correct version for the instrument.
●  Instruments without a front-panel display or a simple one that still can provide an intuitive user interface.
●  Embedded Web-based help to eliminate hunting for lost manuals or CDs.

Embedded Applications
In addition to the capabilities provided by enhanced Web pages, smart instruments can include embedded applications with capabilities rivaling those of discrete applications normally installed and executed on a test- system controller. The peer-to-peer capability of the LAN interface means these applications can involve multiple instruments, allowing small to medium test systems to be constructed without the traditional system controller.

For example, two instruments could be controlled by an embedded application to perform I-V characterization of four-terminal devices. The instrument running the application could use peer-to-peer LAN messaging to control the second instrument and collect data for display on a Web page.

Another benefit of embedded applications is the smaller impact on end applications due to changes in the operating system, I/O libraries, and related software and utilities. In traditional systems, application programs running on a separate computer or controller demand maintenance because they must be retested when those components are updated.

In contrast, Web browsers change less frequently and maintain strict backward compatibility. This translates into reduced maintenance by the vendor, which, in turn, means fewer updates and revisions for the user.

Embedded applications also provide an architectural advantage. A typical application program generally involves interactions between the program logic itself, an instrument driver, an I/O library that supports instrument communications, and the instrument firmware.

Although there are benefits to this type of layered architecture, it also can increase development time and cause maintenance problems. An error in the logic or changes to the instrument can require revisions to all components in the system.

However, with an embedded application, all the necessary logic is contained within the instrument, reducing development time and maintenance. For example, consider a simple application developed to run on a separate controller. The application has a graphical user interface that allows the user to select the measurement range of an instrument. The application uses the IVI driver provided with the instrument and the VISA I/O library to manage communications with the instrument.

Such an application will have logic to check the validity of the user' s range selection in multiple software components. There will be range-checking logic in the user interface logic and perhaps in the main program logic, the instrument driver, and the instrument itself.

However, in the case of an embedded application with the same functionality, all the logic is contained within the instrument so updates become simpler and there is no danger of having incompatible versions of separate components. A further improvement is possible by using a single-range check function within the instrument that is called whenever range validation is required. This eliminates the redundant software code entirely, an ideal solution that is not practical in the stand-alone application.

Some system designers may be concerned about the performance of embedded Web-based applications, especially Java applets. However, many techniques are available to optimize the performance of embedded applications.

In addition, because discrete application programs often use layered architectures, data and commands must pass through each layer, often requiring buffering and reformatting to conform to the standards for each layer. These steps incur extra processing overhead that slows throughput.

However, embedded applications have total control over the data flow from instrument to application. All aspects associated with data and command flow can be fully optimized because there is no need to conform to IVI driver or VISA I/O library formatting standards. For that reason, performance of a Web-based application can be superior to a stand-alone application program implementation.

Scripting Boosts Performance
Adding script-processing capability to smart instruments can greatly improve performance because it supports the concurrent operation of multiple instruments. In a traditional controller-based test system, instruments can experience significant idle time while waiting for the controller to process data from another instrument before sending the next command. Each step in the test program may require several commands be sent to each instrument to prepare for the next step.

With script-processing instruments, each instrument' s portion of the test program can be transferred to it prior to execution. The instruments then can be sequenced through their individual programs using LAN triggers, time-based triggers, or hardware triggers to keep the instruments synchronized and minimize the delay between steps.

In high data-rate or large data-set applications, instruments can post-process data, compressing large data sets or performing sophisticated analysis before the data is transferred to the controller, easing controller or network throughput issues. Scripting and concurrency also can benefit applications that are not controller or network limited. Here, complex problems can be broken into manageable pieces that run independently but also collaborate to solve the larger problem.

In addition to scripting, features incorporated into the LXI standard such as IEEE 1588 clock synchronization, peer-to-peer messaging, and LAN triggers will offer users the ability to develop concurrent test and measurement systems.

Scripting Enables Event-Driven Testing
One strategy for accelerating testing, which avoids bottlenecks in conventional test system architectures, is event driven testing. In this approach, test code embedded in the UUT collaborates with smart instruments to run a series of tests at the fastest possible test execution rate.

The smart instruments are pre-loaded with appropriate test scripts. Once the test cycle has been initiated, the UUT starts and controls the sequence of tests. The UUT can sequence tests using control signals of various types, including hardware trigger lines, Ethernet communications, or some other communications bus.

While this strategy is only applicable to sophisticated UUTs, it provides additional benefits. For example, since the UUT has access to internal data and state information, it is possible to optimize test selection and speed without interaction from a system controller. Preloading test scripts and other configuration information into smart instruments can eliminate controller and communications bottlenecks, improving overall test throughput.

Scripting and Extensible Instruments
Test scripts are an ideal way to extend the functionality of an instrument beyond its base set of functions. Because scripts are executed within the instrument itself, their performance is better, and timing is more deterministic than for an application running on a remote or system controller, regardless of the communications bus used.

For an instrument manufacturer, deploying example programs and small application solutions as scripts greatly reduces its development effort. Normally, such an example program would have to be written in multiple programming languages to suit the needs of various users.

However, when written as a script, it is usable by all users, regardless of their choice of programming language. Writing, testing, and documenting a single example are much easier than supporting multiple versions. Lowering the cost of developing and deploying examples and applications ultimately reduces the total cost of test.

The Future of LXI and Smart Instruments
Several significant enhancements and additions are planned for future LXI specification releases that will further enhance the ability of instrument makers to provide smarter instruments. LXI Identification is a mechanism for obtaining a detailed description of an instrument and its capabilities from the instrument via the LAN interface. Upon request, the instrument will provide an XML document with a structured description of the instrument. This capability is intended to provide an enhanced version of the *IDN? query currently implemented in all SCPI- based instruments.

LXI Resource Management will provide a protocol for managing access to instrument functions and data from multiple clients or controllers. GPIB-based systems, for example, are limited to a single active controller at any time.

LXI systems have no such inherent limitation. LXI instruments with multiple channels or subsystems can be shared by multiple applications or controllers. A power supply with four independent outputs can be used simultaneously for four different test programs. LXI Resource Management also will provide the tools to prevent inadvertent or improper access to a device when it already is in use.

The IEEE 1588 Working Group is pursuing version 2.0 of the specification. When it is released, LXI will require compliance with the version 2.0 specification for LXI Class B devices. IEEE 1588 V2 provides significant enhancements relevant to test and measurement applications. One important change is support for much better timing accuracy.

Conclusion
Smart instruments offer the potential to lower the total cost of test by performing more of the work for users. Limitations in prevailing test-system architectures and communications buses have, until recently, prevented smart instruments from achieving their full potential. LXI technologies and programmable instruments are combining to break through the limitations of the past and allow smart instruments to shine. Planned LXI enhancements will accelerate this trend.

Putting Smart Instruments to the Test The capabilities and benefits of smart instruments can be demonstrated by considering a test system designed to make pulsed RF measurements on an RFIC power amplifier. Testing is done in short pulses (2 ms) to avoid overheating and thermal effects so timing and synchronization are critical design factors. Existing Setup The existing test setup consists of standard instruments; a PC; application programs in visual C, VB, or other ADE; instrument drivers; an I/O library; a GPIB controller and cables; trigger cables; and a controller and communications to determine timing (Figure 1). Figure 1. Existing Setup Possible Future Solution A test system taking advantage of LXI-compliant smart instruments would include LXI Class B instruments with scripting, a PC, an embedded application in each instrument, LAN cables, a hub or switch, and IEEE 1588 timing (Figure 2). Figure 2. Possible Future Setup Benefits The move to smart instruments benefits both the user and the instrument supplier: no software, driver, or I/O library installation and maintenance; no version-itis between software, driver, I/O library, and instrument versions; less costly than GPIB; no trigger cabling; and better performance with timing accuracy tied to IEEE 1588 and optimized communications between application and instruments. Vendors also can reap some benefits. Applications are written only once, eliminating the need for several versions for different ADEs. Also, less maintenance is needed for operating systems and ADE upgrades.

About the Author
Paul Franklin is the manager of Keithley Labs and chairs the LXI Consortium' s Technical Committee. Before joining Keithley Instruments in 2000, he gained more than 20 years of measurement and control industry experience as an engineer and a manager with electronic controls and industrial automation firms. Mr. Franklin earned B.S.E.E. and M.S.E. degrees at Case Western Reserve University and is a member of IEEE, the IEEE Computer Society, the IEEE Instrumentation and Measurement Society, and the Association for Computing Machinery. Keithley Instruments, 28775 Aurora Rd., Cleveland, OH 44139, 440-542-8097, e-mail: pfranklin@keithley.com

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Network Security for LXI Systems

By Mike Dewey, Editor

The ubiquity of LANs and the low cost of Ethernet are features that make LXI a very attractive alternative to other control bus implementations such as GPIB, RS-232, FireWire, or USB. However, unlike test systems that might be controlled by a localized network such as GPIB, systems that rely upon a LAN or WAN must contend with network security issues.

Depending on the specific architecture and span of connections that comprise a LAN-based test system, the requirements for a secure network can vary from minimal to extensive, with each LXI device and the associated system configuration conforming to a company' s IT security policies.

The need for secure networks is universally recognized by all IT organizations. Consequently, implementing an LXI system that uses these same networks requires that test system designers and users apply the adopted policies and procedures to maintain the security integrity of the network.

Understanding Network Security
To understand how the incorporation of an LXI device or the design of an LXI system might impact the overall security of the controlling network, it' s important to know the requirements, policies, and methods associated with creating a secure network. Protecting the integrity of your network and the information transported requires addressing the following questions: How do you protect confidential information that is available on your private network from those who do not explicitly need to access it, and how do you protect your network and its resources from malicious users and accidents that originate outside your network?

Network security involves protecting against a variety of security threats, which can compromise both your network' s information and performance. Several of the more common methods of attack include the following:

Network Packet Sniffers
Network packet sniffers can gain access to system-level account information by monitoring nonencrypted packet traffic. User account information, passwords, and even the integrity of the network can be compromised by intercepting network traffic packets.

IP Spoofing
IP spoofing involves an attacker who can send erroneous or embarrassing e-mail to someone within the organization appearing like it came from a known person within the organization. It also can be used to access user account and password information. The attack could come from within the organization or via a Telnet connection to an SMTP port on the system, which allows the attacker to insert bogus sender information.

Password Attacks
Password attacks can result in an unauthorized individual successfully penetrating the network, compromising a network' s integrity. For example, an attacker could modify the routing tables of the network by having all packets routed to him or her for monitoring prior to delivery, effectively becoming a man in the middle.

Denial-of-Service Attacks
Denial-of-service attacks are somewhat different from other security breaches because they make a network or service unavailable for normal use. Basically, by overloading a service or server, they can effectively shut down a website or server. Depending on a network' s specific architecture and topology, it is possible for a denial-of-service attack to cripple a complete network by flooding it with undesired or useless data packets and providing erroneous information regarding the status of network resources.

Application-Layer Attacks
Application-layer attacks are probably the most visible or at least the most publicized types of security attacks and referred to as malicious software (malware). Viruses, worms, and Trojan horses are all types of malware.

A Trojan horse is any program that invites the user to run it but conceals a harmful or malicious payload. The malicious payload may take effect immediately and can result in many undesirable consequences, such as deleting all the user' s files. More commonly, it may install further harmful software into the user' s system to serve the creator' s longer-term goals.

Trojan horses also can start a worm outbreak by injecting the worm into the user' s local networks. The use of ActiveX controls is a known method for implementing a Trojan horse attack and one of the main reasons that many network computers are configured to disallow the use of ActiveX controls.

A network' s vulnerability to security breaches or attacks can vary depending on the network' s span or perimeter size as well as the number of access points. Generally, the larger the network, the more vulnerable it may be to security incursions. Types of networks include the following:
● LAN— a network that typically operates within a limited part of a building' s floor or area. Private networks also can be classified as LANs.
● WAN— a network of subnetworks that interconnects LANs over a geographical area within a single organization.
● Intranet— a TCP/IP-based logical network within an organization' s internal network structure.
● Internet— a global, public TCP/IP-based network that may be used to interconnect WANs and LANs via a switched or a virtual switched connection using the Internet cloud.
● Virtual Private Network (VPN)— a network where data packets from an internal network are transmitted over the Internet using encryption to ensure a secure connection, resulting in a virtual private connection.

Figure 1 details a simple network that incorporates some of these network topologies.
 

Figure 1. Typical Network Configuration

Regardless of the network' s complexity or size, establishing a secure network involves defining the security perimeter of your network; that is, the outer bounds of the network where traffic is monitored and managed to and from your network as well as defining what users are trusted. To ensure network security, all external interfaces to your network must be controlled including connections to the Internet, PCs, modems, and other network devices including instruments such as LXI devices.
 

All LXI devices conform to current TCP/IP networking standards. When they are connected to a LAN, they will operate in a defined manner. In the case of a network fault such as a duplicate IP address, they will have a benign effect on the network.

Depending on the type and size of a network, various network components will be used, some for simply interconnecting various network devices and others that provide not only connectivity but also a level of security. Network components for interconnecting Ethernet devices, LANs, WANs, and network infrastructure include hubs, switches, routers, and firewalls. Routers and firewalls are key components for constructing a secure network perimeter.

Routers provide the capability to interconnect and isolate multiple networks via high-level protocols such as T