RE: 10xGbE on DWDM

["Bill St. Arnaud" <bill.st.arnaud@xxxxxxxxxx>]

Paul:

> Many industrial research teams: Alcatel, NTT, Nortel and
> BT and university teams: TUD-Denmark, ETH-Zurich, HHI-Berlin,
> have had active research programmes in the optical regeneration
> area for the past decade. Prototypical devices have been built
> and demonstrated, but a market hasn't yet emerged because
> electronics has alays provided a cheaper alternative. I'm not
> convinced that 10xGbE will kickstart the market for optical
> regeneration---a pity. However I believe that 100xGbE WILL!


I think the major issue is cost.  There several trans-oceanic cables (e.g
the new USA-China cable) up to 12,000 km in length that use 100% optical
repeaters.  The technology is there, but as you point out electrical
regeneration is a lot less expensive.  That is why currently CWDM technology
is proving more attractive than DWDM solutions.  I am sure in time that
situation will change.

I suspect in a few years most networks will be 100% optical and data
transparent and many of the debates we are having about the type of coding,
scrambling, etc will be largely irrelevant.  In fact some researchers are
proposing that we use only SDL - simple date link protocols as a replacement
for SONET and/or GbE.  SDL protocols only have a start of packet indicator -
no CRC, no overhead bits, etc

>
> Moreover each network node can have an independent
> local clock; every clock within the network being
> nominally synchronous. Global synchronisation IS NOT
> required much the same as with current Ethernet networks.

Packet over SONET routers and Ethernet networks do not require any form of
global clock hierarchy like traditional SONET networks.  The clock is
recovered internally in both cases.

>
> Also why are Cisco moving away from full-blown SDH/SONET
> functionality with their DPT technology?

I can't speak for CISCO, but DPT is a much more efficient use of bandwidth.
Most SONET systems have an unused protection fiber which DPT can utilize
simultaneously with the working fiber.
/
> Note: Synchronisation between adjacent nodes is not effected
> via SONET/SDH with DPT. What are the deployment plans
> for 40Gbit/s SONET/SDH? Are solutions available now? Soon?


Nortel and NEC have both announced OC-768 SONET products



>
> Ultimately the most compelling advantage of Ethernet lies
> in its modularity and simplicity. Sure even I can plug
> the RJ45 into the wall socket beside me and it works!!!!
> I fear that some of the solutions proposed for 10xGbE so
> far have lost sight of this....and the fact that 100xGbE,
> ...1xTbE will inevitably follow.
>
> 	Keep it simple, keep it serial!



Agree 100%
>
>
> Finally, a plea for tolerance and respect. I think 10xGbE
> is where two communities: Datacomms and Photonics are
> meeting for the first time we really have a lot to
> learn from each other.

Agree 100%

>
> Paul.
>
> p.s.  The EDFA window is not narrow. It's 25THz from
> 1535 -> 1565 nm! Indeed there is an extra 25THz available
> from 1580 -> 1610 nm using next generation EDFAs.
> Plenty of room for expansion!

But it is a lot narrower than CWDM.


>
> The filters and optical sources used for DWDM based
> on Arrayed Waveguide Grating (AWG) technology will
> cost next to nothing when Moore Law economics prevails.
> Just like IC's before them, its only "processed sand"
> festooned with a few choice elements.

Agreed but the same economics will also affect CWDM

Bill