Re: 10xGbE on DWDM
- To: "Langner, Paul (Paul)" <plangner@xxxxxxxxxx>
- Subject: Re: 10xGbE on DWDM
- From: Paul Gunning <paulg@xxxxxxxxxxxx>
- Date: Mon, 07 Jun 1999 15:41:09 +0200
- CC: bill.st.arnaud@xxxxxxxxxx, nrjones@xxxxxxxxxx, nuss@xxxxxxxxxxxxxxxxxxx, bin.guo@xxxxxxx, rtaborek@xxxxxxxxxxxxxxxx, dwmartin@xxxxxxxxxxxxxxxxxx, stds-802-3-hssg@xxxxxxxx, sachs@xxxxxxxxxxxxxx, widmer@xxxxxxxxxx, Iain_Verigin@xxxxxxxxxxxxxx, paulg@xxxxxxxxxxxx
- Organization: Futures Testbed, BT Laboratories
- References: <15A2D77655CDD1118B5500805F6FE87A0281C45A@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx>
- Sender: owner-stds-802-3-hssg@xxxxxxxxxxxxxxxxxx
Langner, Paul (Paul) wrote:
> 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,
> 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
> Any questions on this, let me know.
> From: Bill St. Arnaud [SMTP:bill.st.arnaud@xxxxxxxxxx]
> 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
> > 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
> 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
> optical switches in the near future. The problem with serial speeds
> excess of 10 Gbps is the processing required at switching or routing
> Every router manufacturer I have talked to has found it exceedingly
> difficult to build router interfaces that can work at 10 Gbps line
> 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
> light propagation across the phsical dimensions of the box.
> Right now the I believe the propagtion time of an electrical signal
> "copper on copper" semi-conductors is comparable to the speed of
> 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
> 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
> excellent article in the last issue of Scientific American on this
> 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
> dispersion, for example becomes very significant and now cannot be
> Jitter and BER becomes increasingly tougher and tougher as well.
> I think someday we will reach these speeds but maybe not serially,
> 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
> fortunes of your favourite carrier. Whereas if I can get access to
> fiber I can install my own CWDM system at significantly less upfront
> and I am in control of my own destiny.
> We have actually been going through a detailed economic exercise on
> 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
> 10GbE is "significantly" cheaper than DWDM. Because the regional
> network is
> in a small province the local carrier could not justify the upfront
> 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
> better than the total CWDM 10GbE cost!!
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