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RE: Distance Motion

Title: RE: Distance Motion

I'm not sure I agree with your distinction that a LAN is inside the building and ceases to be a LAN when it leaves. Moreover, for the record, I think the distinction between LAN, MAN, and WAN is somewhat arbitrary and archaic. One of the textbooks (can't remember which one--they say the memory is the second thing to go as one gets older, can't remember what the first thing was) compares a gig link between N.Y. and L.A. to a slow bus inside a computer. In essence, performance is about the same. At one time, the LAN was simply the extent of the shared media or collision domain. As technology has progressed, some of the earlier definitions are simply irrelevant.

We're trying to specify links. As part of this process, we look at the environment in which those links will be deployed and try to make it a little easier. However, all we specify is the link.

Walter Thirion
Level One Communications

> -----Original Message-----
> From: owner-stds-802-3-hssg-distance@xxxxxxxxxxxxxxxxxx
> [mailto:owner-stds-802-3-hssg-distance@xxxxxxxxxxxxxxxxxx]On Behalf Of
> Roy Bynum
> Sent: Sunday, June 20, 1999 11:26 AM
> To: stds-802-3-hssg-distance@xxxxxxxx
> Subject: Distance Motion
> Jonathan, et al,
> I laud your motion to alter the objective definition of "distance" for
> 10GbE.  This has become a major hot topic for fiber optic systems
> implementors, both in metro and long haul services.  The advent of
> active and intelligent DWDM systems has compounded the confusion.
> The issue of distance is one of understanding the difference between
> what is a LAN and and what is not a LAN.  While I may be somewhat
> archane, I have always understood that a LAN was restricted to a
> building.  When it left the building, it was no longer a LAN, it was
> something else.  It did not mater if you were bridging or routing, if
> the data system left the building, the part outside the
> building was not
> part of a LAN.  Just because a broadcast domain could be extended over
> great distances by means of bridges did not make that longer
> distance a
> LAN.  What existed over the non-LAN was a virtual segment, not a real
> one.
> Because of a lack of understanding the implications of optical
> networking, 1GbE included a long haul wavelength and power
> implementation, as an extension of the LAN standard.  It exists in the
> telephony standards of Intermediate Reach.  Optical
> networking provides
> for direct conversion of telephony intermediate reach to telephony
> standard long reach simply by using an optical transducer. 
> In spite of
> what was intended or how it is spoken of; 1000BaseLX is not a LAN
> standard.
> In order for 10000BaseXX to be a LAN standard, it must be
> restricted to
> a 850nm, single mode fiber, PHY.  This would allow the 12.5Gb signal
> rate for 8B/10B block code within the confines of a building.  This
> standard would be a "10000BaseSX".
> On the other side of an L2 data switch, for non-LAN systems, long-haul
> optical networking issues must be considered.  This is an environment
> that has different operational support requirements than a
> LAN.  Getting
> access to the fiber plant is not as simple as tracing it through the
> ceilings, floors, or risers of a building.  In some cases,
> you will have
> to dig up the street, to get access to non-LAN optical fiber.  That
> makes the support costs of non-LAN optical transmission systems a
> totally different economic and business model.
> The economic and business model of GbE in the MAN and WAN
> environment is
> based on the lack of conversion from one L2 protocol to another.  L2
> switching has a major econonomic saving compared to L3 switching.  The
> common equipment and interface costs for L2/L3 switches is .10 to .25
> the costs of L3 only switches.  A major portion of the additional cost
> is the processing required to strip the L2 protocol from the
> L3 and then
> put it back on again.  Because of the lack of L2 conversion, today's
> L2/L3 switches have a much higher density and economic
> savings than any
> L3 only switch, and compare very favorably with the new generation of
> "terabit routers" being developed.  The only problem is that
> there is no
> support for operations of the optical fiber plant in the GbE protocol.
> A seperate "long-haul" version of 10GbE will allow continuence of the
> L2/L3 switch interface and common equipment economic model, while
> providing operations support for non-LAN implementations.  This would
> make a distiction between the short-haul, MMF, 850nm standard and the
> SMF, intermediate/long-haul, 1300/1500/1600nm standard.  This
> will allow
> for different signalling standards; block encoding for LANs
> and scramble
> encoding for MANs/WANs. It will also leverage the existing SONET/SDH
> installations and experience of the common carriers.
> Personally, I think that the addional 25Gbps signalling rate will cost
> more than the savings gained by block encoding.  When the issue of
> launch power is removed, I think that a SONET/SDH signaling
> PHY will be
> less expensive for LAN implementation than an 8B/10B signaling PHY.
> Having seperate standards will also allow for economics, not personal
> viewpoints to define the prevalent implementation for the different
> envionments. 
> Thank you,
> Roy Bynum
> MCI WorldCom