Degrees of Twaddle

Degrees of Twaddle – Peter Heywood

July 18, 2001

4 Min Read
Degrees of Twaddle

"How long is a piece of string?"

Optical networking vendors don't know the answer to that old chestnut any more than you or I (Steve Saunders claims to know the answer, incidentally, but that's just Steve being Steve).

But based on the nonsense they pulled at the NFOEC conference and exhibition last week (in Baltimore, tragically) vendors would surely have an opinion on the correct unit of stringometry ("A cord!" "No, a spool!" "Fool! It's a fur-long!" "You stinking liar...!" and so on).

Basically, when it comes to how to measure different aspects of optical networking, vendors at the show used more benchmarks than a home improvement show.

This isn't just a case of engineers with too many brands of slide-rules in their pocket-protectors, incidentally. A lot of the time a vendor's decision to use one unit of measurement over another is based more on business and marketing considerations than engineering preference. For instance, choosing a really obscure, olde worlde unit of measurement can be a great way to impress investors – and ensure that no-one can work out what your company is really up to (anyone for cubits?).

I first started noticing vendors' measurement mores when Optical Switch Corp. announced its new phase mask developments aimed at making FBGs (fiber Bragg gratings) for chromatic dispersion compensators (see Optical Switch Announces Components).

As it happened, Southampton Photonics Inc. also announced FBG developments aimed at exactly the same application at the same time (see Southampton Ships FBGs, Names VP). And that’s where the fun began.

Optical Switch said its developments could make chirped FBGs (cluck cluck!) with a resolution of 13 nanometers per centimeter, while Southampton Photonics made a big thing of its group delay of plus or minus 3 picoseconds. To be frank, I was in a total fog. How did the two compare? After a lot of heavy number crunching, Optical Switch came to the conclusion that the end result was broadly similar dispersion compensation performance (in other words, who cares?).

Anyhow, that got me started, so I asked other folk at the NFOEC how they measured things. Professor David M. Bloom, a founder of LightConnect Inc. (see LightConnect Comes Into Bloom) came up with a couple of classics.

In the early days of lasers, Bloom says, their power was measured in “Gillettes” – the number of razor blades they could burn through.

Bloom also put me onto A Dictionary of Units of Measurement compiled by Russ Rowlett at The University of North Carolina. It cites some really strange units, including “gillions”, an obscure way of saying thousands of millions (giga-millions) for purist Brits, who think billions should refer to millions of millions. The best one, however, is “degrees Twaddle”, a measurement of specific gravity of liquids denser than water.

This gives me a suitable segue to bring up the degrees of twaddle surrounding another unit of measurement at the moment – the percentage utilization of fiber capacity – which got a big airing at the NFOEC, courtesy of Corvis Corp. (Nasdaq: CORV) and Williams Communications Group (NYSE: WCG) (see Williams, Corvis Lash Back).

In essence, analysts have come up with the notion that having lots of fiber in the ground and using very little of it is bad. This penalizes new carriers unfairly because it hardly costs them any more to install cables with, say 144 rather than 24 fibers in them. It also fails to recognize that modern fiber can support far more DWDM channels than older fiber, giving new carriers an intrinsic advantage over established ones, according to David Smith, VP of hardware engineering at Corvis. On top of that, new carriers may be just getting started on filling their infrastructure with traffic, he notes. See Fiber Utilization Figures Challenged for more on this subject.

Another type of twaddle was evident at a breakfast meeting held by Altamar Networks at NFOEC that I attended. My colleagues at the breakfast reckoned that the price of telecom equipment is nearly always reflected in its size. By that reckoning, someone joked, vendors could sell their gear for so much a pound, like potatoes.

Plenty of other optical networking phenomena are measured in units that non-physicists have trouble getting their heads around – like decibels, which don’t appear to follow a linear scale, and bandwidth measured in GHz rather than Gbit/s. Happily, Light Reading has just published a Beginner’s Guide on this subject: Optical Units Reference.

If you know of some other examples of strange ways of measuring optical phenomena, please share them on the message board following this article.

— Peter Heywood, Founding Editor, Light Reading

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