Cell Relay Archive

[albert.e.manfredi@boeing.com]

In article <8dr8cn$u4s$1@nnrp1.deja.com>,
  zombiesquad@onebox.com wrote:
> All,
>
> I've done some research about sonet and dwdm.  I would like any input/
> insights on two issues that arose.
>
> 1 - Are sonet and dwdm competing technologies?  If so, where do you
see
> sonet heading, will it be overtaken by dwdm?

I think that in many people's minds, they are competing technologies.
Because WDM designs are trying to incorporate a subset of services that
SONET provides now, without providing the services that perhaps are not
needed in future packet-oriented infrastructures (e.g. the strictly
isochronous features that SONET supports).

However, if you put aside all the hype, I think that WDM is just
another one of many TDM-WDM-TDM-WDM iterations.

Why does anyone care about WDM? Because it's supposed to allow one to
make better use of the bandwidth capabilities of fiber cabling. But
haven't we seen this before? Of course we have, with coax cable.

1300 nm lasers over glass fiber have a frequency of 153 THz. Can we
pretend that this is RF, and just modulate that light to carry data? If
we had fast enough electronics, sure, why not?

For example, if we used pure FSK, we coud achieve data rates of 76.5
Tb/s. If we used QAM, we could drive that number way up. Problem is,
today it would be pretty tough to design boxes that could switch
packets at these rates. So we frequency divide, and make use of slower
channels, just as we do when watching over-the-air or cable TV.

> 2 - Is there a future for sonet technology?

I'm sure that SONET will survive as is for many years. But I expect
that we'll go through a frequency division phase again, followed by
another baseband digital phase when we build electronic or optical
circuits that can directly use all of the optical bandwidth. And then
we'll probably invent SONET II for this new baseband digital service.

--
Bert
albert.e.manfredi@boeing.com


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