Tackles jitter on optical transport networks with new upgrade based on latest standards

August 2, 2004

4 Min Read
Agilent Claims Jitter Test Breakthrough

Agilent Technologies Inc. (NYSE: A) claims to have put a serious dent in one of the toughest test challenges facing vendors of 10-Gbit/s Sonet (Synchronous Optical NETwork) and SDH (Synchronous Digital Hierarchy) gear by producing a jitter measurement tool that can save component makers, equipment manufacturers, and their customers time and money (see Agilent Raises Jitter Test Bar).

Agilent says it has upgraded one of its products, the OmniBER OTN communications performance analyzer, to measure levels of jitter, or signal noise, produced by 10-Gbit/s optical gear at a significantly greater accuracy level than has previously been achieved.

That accuracy comes at a price, though. The new product comes in at just more than $200,000 per unit, and although this is an "enhanced" version of the OmniBER product, previous versions cannot be upgraded to perform the exact same tasks to the same degree of accuracy.

Ronnie Neil, market segment manager for Agilent's Data Networks Division, says the breakthrough comes from the application of a callibration procedure based on new International Telecommunication Union, Standardization Sector (ITU-T) standards (O.173 and an amendment to an existing standard, O.172) and "new procedures within our design process" for the OmniBER product.

The result is that Agilent can guarantee that the jitter measurement produced is accurate to within plus or minus 15 mUI (milli-unit intervals), whereas before, the typical, though not guaranteed, accuracy has been plus or minus 35 mUI. As the standard design limit for 10-Gbit/s SDH and Sonet jitter levels is 100 mUI, the reduction in the accuracy range is significant.

Now, if a component is tested and shows a consistent jitter level of 80 mUI, for example, it is guaranteed, according to Agilent, to be within the 100 mUI limit, whereas previously, a score of 80 mUI could have meant the actual jitter level was as high as 115 mUI, which would have made the product unusable.

So under current typical accuracy levels, a score of 65 mUI or less was required to guarantee standard compliance, and it also meant that perfectly good items could register jitter test levels of up to 135 mUI, but would be rejected because of that high score. A shorter accuracy range means less good kit will be failed, and fewer bad items will make their way into vendors' gear and carrier test labs, only to be rejected at a later stage.

"Jitter is inherent in transport networks," says Neil. "Every piece of kit has intrinsic jitter, so it's very important that level can be measured as accurately as possible, but it takes very sophisticated methods to make such meaurements, as the test gear has to be 'noise free' itself."

He says Agilent's new design procedures include a process by which a jitter signal of 100 mUI can be generated, against which the measurements of each OmniBER analyzer can be tested. It also allows for the simulation of different types of jitter with different characterstics, such as spikes, says Neil.

He says Agilent has had its new upgrade put through the mill by several vendors that "are very pleased with this advance."

The end result, says Rick Pearson, marketing manager for the vendor's computing and networking solutions group, is that "vendors can be sure of making better gear. We know they are hit by this jitter problem and that they are shipping products that don't comply with the 100 mUI standard. It also means carriers will be getting better products, and will be able to save on network engineering resources."

Pearson adds that he doesn't believe Agilent's main competitors in the transmission jitter measurement market, Acterna Corp. and Anritsu Corp., can achieve the same levels of accuracy. But Neil says the two rivals, which both contributed to the new ITU standard along with Agilent, "could do similarly, but part of the performance of the product is down to the design process. They'd need to match the quality of our design."

Those competitors could be closer than the Agilent executives think. Back in March, Anritsu announced a product based on the same ITU standard that offers accuracy of plus or minus 20 mUI, and at less than half the price (see Anritsu Tests Jitter the ITU Way). Acterna launched a module for its ONT-50 tester about a month ago (see Acterna Breaks New Test Ground. The company was unable to respond to requests for comment by the time this article was published, but its ONT-50 data sheet says the "measurement accuracy conforms to ITU-T O.172/O.173."

— Ray Le Maistre, International News Editor, Light Reading

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