Conference 7.286::fddi

    Jean-Marc,
       I'm not sure I understand your failure scenario. If you're thinking
    of using SMF for your secondary ring and MMF as your primary, that
    isn't possible (at least not with the products available today). Since
    each cable caiires both the prinary and secondary ring, you'd have to
    have a heterogenous fiber cable to do what you're describing (if I
    understand it correctly). To answer your other questions, yes, you can
    have a concentrator with the A port MMF and the B port SMF, but that
    would just allow you to have varying distances between concentrators.
    And, no, you can't use MMF in a SMF plug. They use different types of
    connectors, not to mention the whole problem with launch powers,
    numerical aperatures, etc.
    
    Debbie
    

Hello again,

Many thanks Debbie for your first answer, I think I have to simplify
my problem...

After Line failure, the configuration looks like following...

Fiber Length  <-2KM->        <-2KM->       <-2KM->
 sssssssssssssssssssssssssssssssssssssssssssssssssssssssssssss
 s  ssssssssssssssssssssssssssssssssssssssssssssssssssssssss s
 s  s  --------      --------      --------      --------  s s
 s  sss! FDDI !------! FDDI !------! FDDI !------! FDDI !sss s
 ssssss! CONC !------! CONC !------! CONC !------! CONC !sssss
       --------      --------      --------      --------
Port  A        B    A        B    A        B    A        B  

ssss SMFiber
---- MMfiber

The idea is to have a full FDDI dual ring even after a line destruction...

Is now our configuration more comprehensible ??

And now my questions again:
---------------------------
I read the Network Buyers's Guide and the Sales Update (Europe June 91)
and I have a lot of configuration questions.
Our configuration is changing from MMF before line failure to SMF after.
 
What are the modules able to have Port A SMF and port B MMF
and the other case Port A MMF and Port B SMF ??
What are the references of these modules for DECconc 500??

Can we put 2 Mgt Card modules in a DECconcentrator 500 , one for MMF
the other for SMF ??

In case of line failure the only solution is ( I think may be I am wrong )
to swap 2 DECconc 500 Mgt Card.
Before failure 
2 DECconc with Mgt Card (A MMF and B MMF)
After failure
1 DECconc with Mgt Card (A MMF and B SMF)
1 DECconc with Mgt Card (A SMF and B SMF)  

I apologize about my ignorance but I think this kind of configuration
is about to be more and more frequent. Actually the Optical Fiber Providers
are pushing more and more optical links with SMF and MMF mixture.

Many thanks for your answers and suggestions...
Best regards,
					      Jean-Marc MOSER
					DECmail= @ZTO  JEAN-MARC MOSER
				  	VAXmail= STRASB::MOSER(47.152)

    Jean-Marc,
       I'll answer the easy questions first. The module for the
    concentrator where the A port is SMF and the B port is MMF is DEFCN-CA,
    for MMF on port A and SMF on port B its DEFCN-DA. You can only have 1
    management card in a concentrator.
    
    Unfortunately, I still don't understand why you want to have the mix of
    fibers. SMF is no more secure or reistant to faults than the MMF. The
    only thing it gives you is the additional distance support. The ring
    will wrap regarless of what type of fiber you're using and therefore
    retain its consistency.  In your diagramm, the SMF wouldn't be used
    even after a failure. The ring would wrap at both ends of the cons
    which were still up, so you would only be running over 1 ring then, not
    a dual-ring.
    
    I hope this makes sense.
    
    Debbie
    

    I suggest you consider this alternative:
    
    Keep the dual ring within one room.
    
    Dual-home all other concentrators to the dual ring over physically 
    diverse cable routes. One route can be MMF, the other SMF. 

Hello,

Some explanations more,

SMF length    <--------------6KM---------------->
 sssssssssssssssssssssssssssssssssssssssssssssssssssssssssssss
 s  ssssssssssssssssssssssssssssssssssssssssssssssssssssssss s
 s  s  --------      --------      --------      --------  s s
 s  sss! FDDI !------! FDDI !------! FDDI !------! FDDI !sss s
 ssssss! CONC !------! CONC !------! CONC !------! CONC !sssss
       --------      --------      --------      --------
MMF Fiber Length  <-2KM->        <-2KM->       <-2KM->
Port  A        B    A        B    A        B    A        B  

ssss SMFiber
---- MMFiber

It's perhaps difficult to understand with such simple drawing.
Between the 4 SER, with FDDI CONC inside, we are planning
to install 2 MMF and 2 SMF. 
In our configuration SMF are ready to provide a backup way if the
normal ring MMF configuration is broken.

I think after reading carefully the answers, that the only way,
to rebuild a dual ring configuration after a disaster on one link,
is to plug  2 new Management Card in the DECconcentrator (Thank you
for the part number).
To execute this operation, we must stop the 2 concentrators at the end
of the broken ring.

With a dual homing configuration, we cannot provide a secure backbone.
The configuration, we are studiing, is the backbone for other building.
The backbone is set up with 7 SER (not only 4 as on the drawing).
From this backbone we are planning to connect 35 other buildings.
Dual homing is looking very complicate...    
Another question, does DEC provide modules with SMF M ports ???

Many thanks for the answers...
Best regards,
					      Jean-Marc MOSER
					DECmail= @ZTO  JEAN-MARC MOSER
				  	VAXmail= STRASB::MOSER(47.152)

    Jean-Marc,
       I think you have a misconception about how FDDI "wraps" when a link
    is broken. I think this is what is causing your confusion (or my
    confusion with your diagram).
    
    Here is your initial config:
    
    
    
    -----                 <-------          -----
    |  A|ppppppppppppppppppppppppppppppppppp|B  |
    |CON|sssssssssssssssssssssssssssssssssss|CON|
    -----                 ------->          ----- A
    p s B                                    s  p
    p s                                      s  p
    p s                                      s  p
    p s                                      s  p
    p s                                      s  p
    p s  A                                   s  p
    -----              <---------           ----- B
    |  B|sssssssssssssssssssssssssssssssssss|A  |
    |CON|ppppppppppppppppppppppppppppppppppp|CON|
    -----              --------->           -----
    
    ppp= primary ring
    sss= secondary ring
    
    
    The light(data) is travelling in the direction indicated by the arrows.
    During normal operation, data is only being carried by theprimary ring.
    As you can see from the A and B ports each connection carries half of
    each ring, the A port containing the primary-in, secondary-out fibers
    and the B port containing the Primary-out,secondary-in fibers. This is
    why you can't have the seondary ring be a different type of fiber than
    the primary ring. Now the distances between the various CONs can be any
    length, e.g. < 2Km or > 2Km. These distances are how you determine what
    type of fiber to use, MMF or SMF. If you were to lose a link somewhere,
    your config would wrap automatically and look like this:
    
    ------                 <-------          ------
    |  A |ppppppppppppppppppppppppppppppppppp|B   |
    |CON1|sssssssssssssssssssssssssssssssssss|CON4|
    ------                  ------->         - ---- A
        B                                    s  p
                                             s  p
    bad link                                 s  p
                                             s  p
                                             s  p
         A                                   s  p
    ------              <---------           ------ B
    |  B |sssssssssssssssssssssssssssssssssss|A   |
    |CON2|ppppppppppppppppppppppppppppppppppp|CON3|
    -----              --------->           -----
    
    ppp= primary ring
    sss= secondary ring
    
    In this diagram, CON1 and Con2 have both wrapped onto the secondary
    ring. This way the data travels along the primary ring until it gets to
    a wrapped station and then it wraps onto the secondary ring and travels
    down the secondary ring. You have maintained your ring availability,
    no connectivity has been lost to any of your stations on the ring. None
    of your distances have changed between CONs, so you don't need
    alternate fiber types. In your scenario in .5, it looks as though
    you're trying to use optical bypasses to bypass stations that have
    failed in the ring and now have created a length > 2km. Again, unless
    you wanted to manually patch onto a SMF data path, then this won't work
    either. 
    
    My suggestion is to let FDDI run the way it was intended to run, let it
    repair itself without human intervention and you'll probably have a
    much more reliable network. FDDI was designed for built-in redundancy,
    that's why it uses the DUAL-ring. Unless I'm missing something, I think
    you're trying to make your network a lot more complicated than is
    necessary, which might lead to more problems than it solves.
    
    Debbie
    

    Re: .5 I forgot to answer your last question. Yes, we do make M boards
    with SMF ports. They come with 2 MMF and 2 SMF ports on each card.
    Order number is DEFCN-FA.
    
    Debbie
     

You should read various documentation to understand better how FDDI deals
with failures.  From .0 and followup I get the impression that you've
missed some key points.

A dual ring recovers from a single cable failure (cable failure = failure
of one or both of the fibers of a fiber pair going between two ports).

A dual ring does NOT fully recover from double failures.  That's why you
should not have a lot of nodes on the dual ring, or have the dual ring
going through many places.  

Tolerance of multiple faults is obtained by building a tree structure,
connected to multiple concentrators on a dual ring, interconnected by
"dual homing".  (See FDDI Primer or other suitable documentation.)

As for single mode, if you want to do some of your recovery by manual
rewiring, and you sometimes need more than 2 km, then just use single mode.
Single mode can be used for ANY distance up to the limit -- even distances
less than 2 km.  However, you MUST be sure to follow the rules for MINIMUM
cable loss, or the receivers will not work (I don't remember if they can
be damaged).  Minimum loss rules are easy to deal with; all it means is
that you sometimes need a cable with an attenuator attached rather than
just a simple cable.

	paul