New gear is intended to speed service deployment

March 9, 2000

4 Min Read
Vendors Put DWDM To The Test -- Sort Of

Baltimore, MD--Vendors unveiled a bunch of new analyzers at this week's Optical Fiber Communication (OFC) conference in Baltimore -- claiming that the products take the pain out of deploying the latest high-capacity DWDM (dense wave division multiplexing) gear and services.

But do they? A closer examination of the feature sets of the new products shows that they fall down in some areas, and are downright feeble in others. For instance, the ability to track specific characteristics of DWDM channels is still MIA, as are customization features. And the products are about as user-friendly as a punch in the face.

New DWDM channel analyzers were shown at OFC by Agilent Technologies Inc., Anritsu Corp., Exfo, GN Nettest, and Tektronix All of these vendors offer diagnostic boxes capable of viewing over 100 DWDM channels.

Up to now, the range of test equipment available for DWDM has been limited to 'scopes' that plot the condition of several channels on a wavelength. But demand from vendors and carriers to increase DWDM channels has led test gear suppliers to multiply the number of channels they can view. As reported previously by Light Reading (see What's Hot At The OFC), GN Nettest takes the prize for monitoring most channels. The vendor's CMA4791 Optical Channel Analyzer can view up to 256 DWDM channels. In comparison, Agilent's 86145A Optical Spectrum Analyzer views 180 channels; Anritsu's MS9720 monitors up to 120; and Tektronix's Q8384 tracks 128. (Exfo's booth staff wouldn't give even this basic information about its FTB 5240 product to Light Reading, although it claims it's designed to compete with the ones mentioned here.)

However, simply being able to monitor a lot of channels isn't enough. It's also important to view channels as clearly as possible. DWDM channel analyzers measure the power and accuracy of optical signals. They do this by attaching directly to the fiber in the network and measuring the strength of the signals traversing individual channels. This information helps determine the degree to which an optical signal maintains its power as it passes through devices and traverses distances in the network. This information in turn helps designers of optical systems determine the right power laser kit and power amplifiers they'll need to make sure light will travel as desired through their equipment.

Vendors refer to an analyzer's ability to measure the strength of optical signals as its bandwidth resolution. The parameters of bandwidth resolution are usually given in terms of the tester's ability to home in on optical frequencies where the distance between wavelengths is narrowest. Thus, the smaller the bandwidth resolution figure a vendor gives, the better. Tektronix bests the competition in this regard, claiming to offer a 10-picometer bandwidth resolution. GN Nettest and Anritsu both claim 50 picometers; and Agilent, 60.

But today's optical channel analyzers lack some key functionality. With the exception of Anritsu, they do not measure the degree to which signals are distorted as they traverse a strand of fiber. This kind of distortion is caused by a range of effects, but it can result in garbled data if it's not controlled. Now, the ability to measure the smudge or smearing of DWDM channels requires specialized hardware such as polarized mode dispersion (PMD) testers, which gauge how the polarization of light affects it performance over distance. These devices are bulky and costly (GN Nettest's PMD analyzer, for instance, costs roughly twice as much as the channel analyzer itself, which starts at $20,000).

Anritsu alone has added integral PMD testing to its MS9720 channel analyzer. A button on the unit activates a PMD test. (No information was available at press time on the level of detail offered by this test.) But each of the vendors interviewed said adding integral PMD testing is an attractive future possibility.

There is also plenty of room for improvement in the area of customizability. "Our engineers want test equipment that is programmable," says a spokesperson for Luxn Inc., which makes optical access platforms. So far, none of the testers offered has a graphical user interface for programming tests, although all support the importing of scripts through text files or the use of command-line interfaces. But not much thought has gone into making these more user-friendly. "Sure, we support scripting-through IEEE whatever," said one Tektronix booth technician.

DWDM channel analyzers are also bulky and expensive. They look, weigh, and cost as much as traditional spectrum and protocol analyzers. Anritsu and GN Nettest say their units start in the "low $20Ks" range; Agilent gives $35,000 as a starting price, and Tektronix's box starts at $43,000. But with all bells and whistles, vendors acknowledge that most systems will run nearly twice the starting price.

-- by Mary Jander, senior editor, Light Reading

Subscribe and receive the latest news from the industry.
Join 62,000+ members. Yes it's completely free.

You May Also Like