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Re: 10xGbE on DWDM

Hi Paul,

much obliged,



Langner, Paul (Paul) wrote:
> Hi,
>  Martin Nuss asked me to forward you a link on some SDL specs, etc.  They
> can be found at:
> <>
>   Some additional comments:
> 1) SDL was designed to correct some flaws in POS, and can be used to map
> data into any bit oriented link (i.e. into SONET or directly over fiber,
> etc.)
> 2) It uses x^48 set/reset scrambling as opposed to x^43 self-sync scrambling
> as the x^43 is open to DC balance/transition density attacks on
> clear-channel mappings.  In non-clear channel mappings (such as STS-12 in an
> OC-48) there are no issues and x^43 SSS works fine.
> 3) It suffers no byte expansion as seen by things such as 8B10B or byte
> oriented HDLC.
> 4) It has 2 messaging channels that allow 6 byte messages to be passed
> between ends of the link (i.e. you can map GbE out of band signalling into
> these).
>   Any questions on this, let me know.
> P
>         ----------
>         From:  Bill St. Arnaud []
>         Sent:  Sunday, June 06, 1999 3:44 PM
>         To:  Paul Gunning
>         Cc:  bin.guo@xxxxxxx; rtaborek@xxxxxxxxxxxxxxxx;
> dwmartin@xxxxxxxxxxxxxxxxxx; stds-802-3-hssg@xxxxxxxx; sachs@xxxxxxxxxxxxxx;
> widmer@xxxxxxxxxx; Iain_Verigin@xxxxxxxxxxxxxx
>         Subject:  RE: 10xGbE on DWDM
>         Paul:
>         > I fully concur. I would welcome a pointer as to where I could
>         > find out some more information about the SDL protocol(s). It(they)
>         > sounds very, very interesting.
>         Lucent has been doing a lot of work in this area.  I can't point you
> to a
>         specific paper, but I have seen numerous presentations from Lucent
> on SDL.
>         Their web site might be a good place to start.
>         >
>         >
>         > I realise that. But is there a requirement for additional
>         > frame overhead in that you need a contiguous sequence
>         > of preamble "training" 'bits' at the front of the frame
>         > to phase sync. the Rx PLL?
>         If you have loss of sync that may be required, but in general I
> don't
>         believe there is a requirement for "training" bits
>         >
>         > Agreed. But there ARE clock management issues between
>         > adjacent nodes on a DPT ring in that you have to
>         > explicitly nominate a master and slave relationship.
>         Hmmm.  I will have to check into this.  DPT and Nortel's IPT which
> is very
>         similar allow for auto-discovery etc which implies that there is no
>         master/slave relationship.
>         > Unfortunately I can't attend the meeting in Idaho
>         > but I would be very interested to learn of any proposals
>         > for 100xGBe.
>         I remain skeptical that we will see serial speeds beyong 10Gbps or
> "all"
>         optical switches in the near future.  The problem with serial speeds
> in
>         excess of 10 Gbps is the processing required at switching or routing
> nodes.
>         Every router manufacturer I have talked to has found it exceedingly
>         difficult to build router interfaces that can work at 10 Gbps line
> speeds.
>         To do this a router must process an incoming packet, perform a
> 256,000 entry
>         address table lookup and the forward the packet across a backplane
> in a few
>         nanoseconds.  At these speeds we are closely the physical limitation
> of
>         light propagation across the phsical dimensions of the box.
>         Right now the I believe the propagtion time of an electrical signal
> for
>         "copper on copper" semi-conductors is comparable to the speed of
> light
>         through glass. But more importantly is the small component size of
>         semi-conductors versus existing opto-switching devices.  At these
> speeds the
>         size of components and the length of their interconnection path
> becomes very
>         critical for high speed processing.  As I understand it when you try
> to
>         reduce optical components to the size and density as semi-conductors
> you are
>         approaching the wavelength distance of the actual light path which
> causes a
>         whole set of new refractive and light bending problems.  There was
> an
>         excellent article in the last issue of Scientific American on this
> topic.
>         Finally when you have serial speeds in excess of 10 Gbps you run
> into a
>         whole set of new non-linearities in the fiber itself. Polarization
> mode
>         dispersion, for example becomes very significant and now cannot be
> ignored.
>         Jitter and BER becomes increasingly tougher and tougher as well.
>         I think someday we will reach these speeds but maybe not serially,
> perhaps
>         through Silkroad's or Transact's technology solutions.  But I don't
> see it
>         happening for several years.
>         >
>         > Yes. But deployment economics would tend to prefer DWDM
>         > so as to maximise bandwidth per physical fibre. DWDM allows
>         > you to have many additional "virtual" fibres per physical fibre.
>         The same economics apply to supercomputers.  The cost per memory bit
> of a
>         supercomputer is significantly less than that of a a standard PC.
> It would
>         be more economical to move all our applications to supercomputers.
> But you
>         don't see many people doing that.
>         I think the same rationale will apply to DWDM.  Yes, the cost per
> bit is
>         signficantly less than CWDM and yes you can pack in many virtual
> paths.  But
>         the upfront capital is very high.  More importantly you are tied to
> the
>         fortunes of your favourite carrier.  Whereas if I can get access to
> dark
>         fiber I can install my own CWDM system at significantly less upfront
> cost
>         and I am in control of my own destiny.
>         We have actually been going through a detailed economic exercise on
> this
>         very topic for a 1700 km regional network here in Canada.  Even a
> very big
>         manufacturer of DWDM equipment had to admit that CWDM, particularly
> with
>         10GbE is "significantly" cheaper than DWDM.  Because the regional
> network is
>         in a small province the local carrier could not justify the upfront
> capital
>         cost of a DWDM system.  But even if the carrier had the business
> case to
>         justify the upfront capital cost,  the prorated DWDM cost was not
> much
>         better than the total CWDM 10GbE cost!!
>         Bill
>         >

Paul Gunning
Futures Lab
BT Laboratories

Phone:	+44 1473 647049
Fax:	+44 1473 646885
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