Subject: RE: Optical IP activities

From: "Peter Ashwood-Smith" <[email-masked]>
Date: Sat, 18 Mar 2000 01:17:20 -0500

> All I'm saying is that optical
	>networks
	>have special requirements and we need to understand them better
before
	>deciding if we should use peer model or overlay model. May be we
should
	>have both.

	I don't think anything we have done so far has decided on one model
v.s. the other. It is perfectly possible to use MPLS traffic engineered
paths as part of a flat (peer) model or an overlay model regardless of the
transport mechanisms used. The point I'm trying to make are that all of
these overlay v.s. peer arguments are orthogonal to the transport mechanism
in use and that one should not abstract along transport domain boundaries ..
if you have an alternative.

	>> Optics is not really special, its just really fast
	>> with a few new interesting constraints many of which 
	>> will disappear within a few years. 

	>Why do you think that the constraints will disappear within a 
	>few years? 

	Just taking three constraints as examples. There are many others but
consider these as illustrations...

-	reach - the distance a pulse can travel before it either spreads
into other pulses or is too weak to be detected. Bounding it requires a
route computation that knows the length (delay) of the individual links
probably taking into account the presence of amplifiers. This is not a
particularly difficult constraint to take into account but I'll admit the
amplifiers are tricky to incorporate into an OSPF type model. Fortunately
reach has increased steadily over the last  10 years and will almost
certainly continue to do so as tighter modulation and detection devices are
built. Solitons for example, promise near unlimited reach.

		 - distortion caused by wavelength conversion. The devices
used to do wavelength conversion produce the      difference between the
input wavelength and a reference wavelength. They also produce other
undesirable products above and below the output peak. One way to deal with
this is to switch entire bands of wavelengths or wavebands instead of
individual wavelengths. This actually introduces another level of logical
label to the label hierarchy, one that nobody has really talked about yet.
This is one area where logical abstraction has a direct physical advantage
since it allows much tighter lambda spacing. I was planning to bring this up
in the optical BOF.

-	wavelength conversion incapable devices, can be handled by
establishing paths with the same label, over CI segments as shown in
draft-fan and others. This constraint can be dealt with locally by the
signaling protocol without requiring flooding of the available wavelengths
at the expense of a bit of trial and error from time to time. It is clear
thought that as wavelength difference devices get cheaper and tighter this
will be the preferred switching mechanism although we will still want to
reduce the number of wavelength changes end to end for distortion reduction
purposes. 

I guess the ultimate perhaps cynical reason why constraints disappear is
simply greed! Although I guess we will be stuck with C for quite some time
despite work by  some of our marketing departments to address it.

Cheers,

Peter

---

From: "James V. Luciani" <[email-masked]>
Date: Sat, 18 Mar 2000 23:13:38 -0500

RE: Optical IP activities>reach - the distance a pulse can travel before it
either spreads into other pulses or is too weak to be detected. Bounding it
requires a >route computation that knows the length (delay) of the
individual links probably taking into account the presence of amplifiers.
This is

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.  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.

>not a particularly difficult constraint to take into account but I'll admit
the amplifiers are tricky to incorporate into an OSPF type model.
>Fortunately reach has increased steadily over the last  10 years and will
almost certainly continue to do so as tighter modulation and

Well... solitons do have the benefit of reduced or no chromatic dispersion
but they are still subject to attenuation and need amplifiers.  There is the
nasty reality that there is a lot of dispersion shifted fiber out there (not
to mention the stuff optimized for 1310).  The point again being that it is
not merely a matter of query-replace-reg-expr between "optical" and
"electrical" as was previously suggested when talking about route
calculations.

>detection devices are built. Solitons for example, promise near unlimited
reach.

> - distortion caused by wavelength conversion. The devices used to do
wavelength conversion produce the      difference between the >input
wavelength and a reference wavelength. They also produce other undesirable
products above and below the output peak. One
>way to deal with this is to switch entire bands of wavelengths or wavebands
instead of individual wavelengths. This actually introduces

draft-ip-optical-framework-00.txt talka about this a bit under the term
multi-link trunking.

>another level of logical label to the label hierarchy, one that nobody has
really talked about yet. This is one area where logical >abstraction has a
direct physical advantage since it allows much tighter lambda spacing. I was
planning to bring this up in the optical >BOF.
>wavelength conversion incapable devices, can be handled by establishing
paths with the same label, over CI segments as shown in >draft-fan and
others. This constraint can be dealt with locally by the signaling protocol
without requiring flooding of the available >wavelengths at the expense of a
bit of trial and error from time to time. It is clear thought that as
wavelength difference devices get >cheaper and tighter this will be the
preferred switching mechanism although we will still want to reduce the
number of wavelength >changes end to end for distortion reduction purposes.