Conference 7.286::fddi

As I understand it, SONET isn't a network (in the sense in which we use
the term) but rather a data channel.  It transfers bits from one point
to another, at various speeds.  The idea is that it can be used instead 
of dedicated wires/fibers, especially when those are provided by phone
companies or the like.

So SONET doesn't compete with FDDI.  Instead, it will at some point become
one of the media over which FDDI can run, just as multi mode fiber is an
FDDI medium today and single mode fiber will be soon.  Which of these you
would use to build your FDDI network will vary, depending on distance, cost,
government regulations, etc.  For that matter, parts of an FDDI network
may be made from one medium and parts from another: if you have a ring
split between two buildings that are 10 km apart, you would have to run
single mode fiber (or perhaps SONET) between the two buildings, but all
the other fibers within each building would normally be multi mode.

	paul

    For some info on SONET, B-ISDN, DQDB (QPSX) et al, you might want to
    see my paper "Public Networks in the 1990s:  Future Wide Area
    Telecommunications Technologies".  It's about 1000 blocks .PS
    currently world read at
    
    CARAFE::USER1:[GOLDSTEIN.DOC]FWATT2.PS
          fred

    the file in 30.2 is not open for world read.  can this be changed?
    
    secondly, does anyone know if we/DEC have formed business partnerships
    with any experienced SONET design/implementation companies either at
    the Corporate level or out of local/regional offices?  or better yet, 
    does such design/implementation delivery *experience* lie within DEC?
    
    I heard of my first SONET opportunity last week, and the customer is 
    already talking with ATT for both services and product.  
    
    					Thx, Stan
                                                         

    just got word from author.  file in .2 updated to FWATT3.PS, not FWATT2.PS

    Just where does FDDI and SONET fit?  Can FDDI run over SONET?  Are
    there any proven sites doing this or is it all smoke and mirrors
    at this point in time?
    
    Regards,
    dmm

There is an FDDI over SONET draft standard in the works (being driven by
Buzz Rigsbee from Boeing, in fact) but it's not done yet and last I looked
-- which was about 1/2 year ago -- it seemed stalled for some reason that
wasn't particularly obvious.

It's not at all clear that running FDDI directly over SONET (as opposed to
routing/bridging it onto ATM running over SONET) is going to be what people
will want in the long run.

	paul

    Sonet with its counter-part in Europe called SDH is a transmission
    technology but not a switching technology. It will replace in the
    future (3-4 years from now) existing leased lines facilities offered by
    telco or carriers. It will run high speed from 52M upto 2.4 gigabits.
    It carries its own signalling and management protocols. 
    Consequently, I am not so sure SONET makes sense when talking about
    FDDI. It is to be the transmission platform possibly for B-ISDN when
    combined with ATM switching technologies.
    Sonet will apply in the WAN space, not on the LAN side.
    

I agree with you that SONET/SDH does not make a great deal of sense with FDDI,
but it does make some sense.  Here's why:

If you want to run FDDI between buildings, you often need to go a longer
distance than 2 km, the multimode fiber limit.  So you would use single mode
fiber.  If the link is on private property, that's no problem (in most 
countries) -- you simply string single mode fiber and connect it.  If the
link is not all on private property, you usually have to get it from the
phone company, which has the monopoly on providing links across public land.

So you go to the phone company and ask for "dark fiber".  It turns out that
phone companies often do not like to provide that.  What they prefer to provide
is a transmission service (such as SONET).  This makes some sense: SONET makes
more efficient use of their facilities.

This is exactly what happened to Boeing some time ago.  They needed to connect
several buildings in Seattle.  Since Boeing is a big company in Seattle, they
managed to force the phone company to provide dark fiber, but the message they
got was clear: SONET is what the phone company really preferred to sell.

So that's why there's now a project to define how FDDI will use SONET as a
transmission service -- in other words, how it will use a SONET facility as
a substitute for a dark fiber connection.  (And that's why the representative
from Boeing is the chairman of that subcommittee...)

	paul

    Sonet, although a physical layer transport medium, does have
    "Cells","packets","Frames", Superframes" or whatever one would like to
    call them.  The beauty of SONET is that each "Frame" can contain
    multiple protocol types within the same frame. Therefore can carry, at
    the same time x.25, fddi, isdn, b-isdn,ipx,atm, frame relay. etc.

That's hardly a novelty of SONET.  SONET is a TDM scheme, and those have
been around for ages.  (Consider T1/T3/etc.)  The thing that makes SONET
significant is that it is an international standard (unlike T1 etc. which
is US or at best North America but not applicable in Europe), defined for a
large range of speeds (51 Mb/s up to 9.6 Gb/s), defined for speed ratios
that are integers (as opposed to funny fractions as in T1/T3) with a consistent
format for all speeds.

	paul