Subject: RE: Optical IP activities

From: "Peter Ashwood-Smith" <[email-masked]>
Date: Sun, 19 Mar 2000 11:15:03 -0600

>You may find quite a few people who are doing amplifier placement
analysis
	>who might disagree with you especially when you talk about doing
dynamic
	>optical bypass/cut-through with no OEO.  So for example, if you
cascade
	>several amplifiers for a single segment, the nonlinear
characteristics of
	>one amplifier can be offset by a subsequent amplifier.  Today this
balancing
	>act is done by hand. 

	     Clearly it is going to be hard if not impossible to deal with
hand placement of amplifiers in a dynamic routing algorithm. (Unless we can
have dynamic control over the amplifiers' gain!) I imagine that a dynamic
system will have to be more conservative in terms of wavelength spacing,
amplifier placement and reach so that solutions computed dynamically
actually work.  Where these tradeoff's are in the cost performance curve
today, I have no idea. 

	    Analogy on: It's a bit like making a super high performance
motor, lots of hand tweaking, costs a fortune, no interchangeable parts etc.
The alternative is a lower power one, cheap to make, easy to maintain,
interchangeable parts etc. We see this trend in high technology all the
time, we always eventually end up picking a point on the price performance
curve to suite use by ordinary folks. A modem is a good example, we could
probably hand tweak many connections to reduce noise, cross talk etc. and up
the speed of that PARTICULAR link, but its just not cost effective so we
make "good-enough-works-almost-anywhere" equipment. 

	> Now lets introduce highly dynamic optical bypass
	>(i.e., non OEO passthrough) capabilities via lamda switching.  You
may find
	>that delicate balance is not so easy to maintain.  Another example
would be
	>amplified spontaneous emission in EDFAs which are cascaded in
optical bypass
	>systems with a large number of amplifiers.  We caould also talk
about
	>polization effects in cascaded EDFAs.  So the point is that, when
you are
	>talking about optical bypass systems the equation gets a lot uglier
than a
	>simple shortes path first calculation because of inherent issues
with the
	>optics which are different from electrical issues.

	    Agreed, but these are not I believe justification for forcing an
overlay model. Just because there are more constraints that need to be
considered to compute an effective end to end optical path and that this
computation may initially be N^3 or N^4, does not mean that we should hide
behind an overlay. The only justification I can think of would be for
optical switching technology that is still so fragile that it cannot be
dynamically controlled....yet. One could deal with such technology by having
these hand tuned, highly optimal paths known to the topology as a link or
FA. So you are in a sense overlaying because you have no choice, but for
other dynamically controllable paths you stay flat.

	    What would be extremely useful would be a taxonomy of the
different constraints, what algorithms are known to deal with them, what's
the cost of relaxing the constraint etc.  Any volunteers? Any good
references?

	    Cheers,

	    Peter

---

From: "James V. Luciani" <[email-masked]>
Date: Sun, 19 Mar 2000 20:26:23 -0500

RE: Optical IP activitiesYou got to love these analogies. :-)

>    Analogy on: It's a bit like making a super high performance motor, lots
of hand tweaking, costs a fortune, no interchangeable parts >etc. The
alternative is a lower power one, cheap to make, easy to maintain,
interchangeable parts etc. We see this trend in high >technology all the
time, we always eventually end up picking a point on the price performance
curve to suite use by ordinary folks. A >modem is a good example, we could
probably hand tweak many connections to reduce noise, cross talk etc. and up
the speed of that

I agree with what you are saying for the most part.  I suppose what I am
also trying to say is that it is not clear to me that we know how to find
out what is "good enough" for every possible optical path, apriori, in a
complex network with a large diameter.   We might need to design a path
integrity protocol to make sure that a given path is usable end to end (drop
to drop I suppose). At the risk of making folks sick, it might be useful to
see if there is a way to make this part of the setup processing.  I
certainly don't want all possible parameters to be part of the path
calculation lest we get O(n^k) for large k as result of number of
constraints.  And you are correct, it might not be a problem but I get a
little nervous when folks say something like this is simple.

>PARTICULAR link, but its just not cost effective so we make
"good-enough-works-almost-anywhere" equipment.
>>(i.e., non OEO passthrough) capabilities via lamda switching.  You may
find
>>that delicate balance is not so easy to maintain.  Another example would
be
>>amplified spontaneous emission in EDFAs which are cascaded in optical
bypass
>>systems with a large number of amplifiers.  We caould also talk about
>>polization effects in cascaded EDFAs.  So the point is that, when you are
>>talking about optical bypass systems the equation gets a lot uglier than a
>>simple shortes path first calculation because of inherent issues with the

I actually did not mean to suggest that we have to force only an overlay
model.  I did strongly intend to suggest that it might be the right choice
though and that suggesting that the peer model is a simple bit of
engineering might be inaccurate.

>    Agreed, but these are not I believe justification for forcing an
overlay model. Just because there are more constraints that need to >be
considered to compute an effective end to end optical path and that this
computation may initially be N^3 or N^4, does not mean >that we should hide
behind an overlay. The only justification I can think of would be for
optical switching technology that is still so >fragile that it cannot be
dynamically controlled....yet. One could deal with such technology by having
these hand tuned, highly optimal >paths known to the topology as a link or
FA. So you are in a sense overlaying because you have no choice, but for
other dynamically >controllable paths you stay flat.

Good point.  And I volunteer to read whatever you write on the subject.
OK.. I will even do my part if you want to start.

>    What would be extremely useful would be a taxonomy of the different
constraints, what algorithms are known to deal with them, >what's the cost
of relaxing the constraint etc.  Any volunteers? Any good references?

--JIm

---

From: Debanjan Saha <[email-masked]>
Date: Mon, 20 Mar 2000 09:37:24 -0600

> 
>      Agreed, but these are not I believe justification for forcing
>      an overlay model. Just because there are more constraints that
>      need to be considered to compute an effective end to end optical
>      path and that this computation may initially be N^3 or N^4, does
>      not mean that we should hide behind an overlay. 

No one is forcing an overlay model. However, I believe that an overlay
model is 
useful in containing the complexities/idiosyncrasies of an optical
network 
within the the optical domain, at least in the short term. Mean while,
we 
can debate how much of this  information should be abstracted and
disseminated 
to the routers; and what do we gain from that and at what cost.  

>      The only
>      justification I can think of would be for  optical switching
>      technology that is still so fragile that it cannot be dynamically
>      controlled....

I am not sure if I agree with this "fragility" argument. Different
physical
layers have different constraints and they may be inherent and
permanent.

>      different constraints, what algorithms are known to deal with
>      them, what's the cost of relaxing the constraint etc.  Any
>      volunteers? Any good references?

I agree! I can give it a shot, but I need help/input from people in the
list.
Debanjan

---

From: "Peter Ashwood-Smith" <[email-masked]>
Date: Mon, 20 Mar 2000 10:57:46 -0500

> layers have different constraints and they may be inherent and

   For example:

       If we have to adjust amplifier gain as a function of the set of wavelengths
traversing that amplifier or we have to adjust gain for some other reason that is
affected by the end to end establishment of new optical trails then we have a problem
controlling this dynamically. Currently the amplifiers are hand placed and hand 
tuned. If we have to dynamically control the gain then you need a control path to
the amplifier. In this case, overlay or not, its not really suitable for dynamic 
path establishment. If this is the case then you have to be a bit less ambitious and
either drop the speed, space the wavlenghts out a bit, or up the power levels at
the edges if you want generic dynamic routing/switching to be able to control it.

> I agree! I can give it a shot, but I need help/input from people in the

  Count me in. Perhaps we can suggest this at the optical BOF. I think many of
us have a rough idea what some of the constraints are but where they stand "today"
and are likely to stand in a few years time is hard to get a handle on and
affects how/what we decide to signal and to constrain against.

  Cheers,

  Peter

---

From: "James V. Luciani" <[email-masked]>
Date: Mon, 20 Mar 2000 11:19:05 -0500

Peter,
  Hope you do not mind me cc'ing the ip-optical list on this.  Good
suggestion.  I think this is an excellent work item for ip-optical if it
were to become a WG.  Not to mention a service to folks who are actually
developing this stuff.

> affects how/what we decide to signal and to constrain against.

--jim