Subject: Comments on draft-ip-optical-framework-00.txt

From: Khaled Elsayed <[email-masked]>
Date: Mon, 20 Mar 2000 16:22:44 +0200

In draft-ip-optical-framework-00.txt, the following is quoted:

>    The network model considered in this draft consists of of IP routers 
>    attached to an optical core network, and connected to their peers 
>    over dynamically established switched optical paths. The optical core 
>    itself is assumed to be incapable of processing individual IP packets. 
>    The interaction between the IP routers and the optical core is over a 
>    well-defined signaling and routing interface.

and 

>    It is not necessary to have a wavelength converter at every switching 
>    element.  A number of studies have attempted to address the issue of 
>    the value of wavelength conversion in an optical network. Such studies 
>    typically use the blocking probability (the probability that a 
>    lightpath cannot be established because the requisite wavelengths 
>    are not available) as a metric to adjudicate the effectiveness of 
>    wavelength conversion.  The IP over optical architecture must take 
>    into account hybrid networks with some OXCs capable of wavelength 
>    conversion and others incapable of this.

I have a question/comment regarding blocking probability in the
optical domain (in general, not specific to this draft). Is it
foreseeable that in an all-optical network a connection from say
point A to point B within the optical network will be subject to
blocking?? I am speaking about connections at OC-48 and OC-192
speeds which are likely to be backbone connections and
aggregation of traffic from various routers or ingress points. Is
it practical to consider blocking as a possible event in such
very high speeds? Maybe connections can be blocked in the ingress
points, but those provisioned connections in the core are usually
ON all the time. (Similar to most carrier backbone networks
today?)

Also, many studies have considered dynamic traffic models and
subsequently made all these wonderful calculations/simulation for
blocking probability. Is dynamic traffic and dynamic optical path
a suitable model for an all-optical network? I can foresee a
traffic matrix that will take weeks or months to change in the
backbone, and such traffic should be handled well in advance with
proper Traffic Engineering. So, what does dynamic traffic and
dynamic path mean in such contexts?

Thanks,

Khaled Elsayed

---

From: "Peter Ashwood-Smith" <[email-masked]>
Date: Mon, 20 Mar 2000 10:42:17 -0500

> ON all the time. (Similar to most carrier backbone networks

  You may waste enormous amounts of bandwidth if you cannot do
wavelength conversion. Convert the question to the ATM domain and
imagine how an ATM network would operate if you had to use the 
same VCC from end to end. Basically, if you do not have the ability
to change "labels" then you need one label for EVERY unique path
through the network. Given that the number of paths through a network
grows what .. N factorial? You run out of labels very quickly. This is 
especially true with DWDM equipement which may only support 50-100 "labels".
This means that a tiny  network would exhaust all the labels/paths
AND you have many links that you can only use a small percentage of
the available "labels" ie bandwidth. So its a very unsatisfactory
solution. Also, to do a good job of it, you need a global view of
each path and label it will use.

   The flip side is full blown wavelength conversion at every hop.
This makes the routing/signalling problem much simpler since you
only have to know if A label is free, not which one. This is the same
as knowing that bandwidth is free so all our exisiting ATM/MPLS-TE style
traffic engineering solutions can compute routes. Ideally though
you want to do wavelength conversion only where you have to .. to
"skip" past a link that is using the wavelength you want. In this
manner you can reduce the distortions created by the conversions.
This is kind of a hybrid approach that the signalling protocols can
take into account by trying where possible to reuse the same "label".

   Anyway, just because bandwidth is "huge" by todays standards and
"up times" are long, does not change the fundamental problem of 
blocking of paths. Remember, long "up times" means looooong blocking
times and "huge" bandwidth means long blocking times with huge 
amounts of bandwidth that are unusable. Not a pretty picture.

> dynamic path mean in such contexts?

   Optical networks do not introduce anything all that new with 
respect to traffic flows. The key points are that the bandwidth is
no longer statistically usable accross all the wavelengths and
there is of course no QOS ... all photons are created equal .. 
at least as far as we know ;) These aspects of optical networking
make statistical multiplexing and different per hop behaviours
impossible and in many ways simplify the engineering job in the
core of the network. Actually in many ways its back to the behaviour
of the TDM circuit switched devices ... i.e. everybody is equal and
everybody gets the same chunk of bandwidth ... just a MUCH bigger
slice. Anyway, I know I'm not answering your question, more
rambling around the edge of it .... 

   Cheers,

   Peter

---

From: Jagan Shantigram <[email-masked]>
Date: Mon, 20 Mar 2000 16:44:30 -0500

>ON all the time. (Similar to most carrier backbone networks

This is a good reality check question. While we do not forsee
WDM networks to be as dynamic as ATM or even traffic engineered
MPLS, it will probably have a topology that is subject to change
by periods of day. This variation too, in the near to mid-term, should
be a well studied and caliberated variance - in the sense that
the provider will know what the three or four different traffic
patterns are that need to be supported. In the long term, however,
we do expect more dynamic nature to creep in to WDM provisioning
which, along with lowering costs of devices, will make the
conversion more and more compelling.

When we have lambda conversion and given a set of traffic patterns
that need to be supported, the number of wavelengths channels
that have to be provisioned can be easily determined. Given the
maximum channels needed on each link, the number of fibers
and the wavelengths per fiber can be determined. Considering that
we may have a good solution for routing the traffic we can
efficiently use the fibers that are in the ground.

When we do not have lambda conversion however, this problem cannot
be solved optimally.. it is akin to the graph coloring
problem - which ofcourse has heuristics that can get us to
a factor (?) of the optimal solution. So, connections may
be blocked even though there is capacity on the fiber to
support it, just because the wavelength is already used up.

>dynamic path mean in such contexts?

I suspect this is a provisioning issue. Currently it is a nightmare
to provision for the expanding needs of customers.. with advanced
intelligent optical systems, fatter pipes can be provisioned as easy
as ordering a pizza? I will however humbly defer to those who know
more about the need for dynamic optical path setup and traffic
mgmt.

-jagan.

>Khaled Elsayed
Shantigram Jagannath
Photonex Corporation

---

From: Khaled Elsayed <[email-masked]>
Date: Tue, 21 Mar 2000 13:35:29 +0200

Hello Peter,

> each path and label it will use.

I am not questioning the usefulness of wavelength conversion. It
is definitely a good mechansim. (Although I have seen some
research work that claims that wavelenght conversion may not be
worthwhile in some scenarios).

> take into account by trying where possible to reuse the same "label".

I agree again.

> amounts of bandwidth that are unusable. Not a pretty picture.

This is what my question is about: will carriers or service
providers afford to block those optically switched connections???
 
> everybody gets the same chunk of bandwidth ... just a MUCH bigger

This is what I was trying to say/discuss. But again, coming up
with a well-engineered network design for WDM/DWDM with the
constraints on wavelength conversion for whatever traffic model
(dynamic or static) is still a challenging problem.

Khaled Elsayed

---

From: Khaled Elsayed <[email-masked]>
Date: Tue, 21 Mar 2000 13:55:35 +0200

Hello Jagan,

> support it, just because the wavelength is already used up.

Connections can be blocked when?? At service provisioning time or
at the time the connection is requested?? My point is a
connection of 2.48 Gbps is not likely to be a random event or an
ATM-like SVC. If a customer would require such huge bandwidth, it
would need that BW to go through or it would better look for
another carrier that will provide a TDM/leased line?? Of course
wavelength conversion can help build a better-utilized network,
no question about that.

Khaled

---

From: Lee Thomas <[email-masked]>
Date: Tue, 21 Mar 2000 17:20:56 -0600

Khaled,

Could you provide links to some of this research or describe some scenarios
where wavelength conversion may not be worthwhile?

Thanks,

Lee

---

From: Jagan Shantigram <[email-masked]>
Date: Tue, 21 Mar 2000 18:47:29 -0500

Khaled,

>My point is a
>ATM-like SVC. 

Agreed - atleast not for some time (2 years? 5??)

>Of course

Agreed again. Service providers will ofcourse do their own
cost-benefit to see if it makes sense.

-jagan.

>> more about the need for dynamic optical path setup and traffic

Jagannath Shantigram
Photonex Corporation

---

From: Curtis Villamizar <[email-masked]>
Date: Wed, 22 Mar 2000 12:52:17 -0500

> wavelength conversion can help build a better-utilized network,

The exception to the rule that "a connection of 2.48 Gbps is not
likely to be a random event" is where a very major event, possilble
external to one's own network results in a shift in traffic patterns
that is significant enough to require that additional lambdas be added
to existing paths.

The real world example in the ISP world is a failure of a peering
point of some sort, a provider interconnect, a NAP or NAP connectivity
of some party.  Since all major ISPs are connected to each other at
more than one geographically diverse peering point, the traffic will
still flow, but the path will have changed.

This may mean that a path that previously required 3 lambdas (for
example), now requires 4 lambdas.  There are at least 3 ways to
accommodate this requirement:

  1.  An external management system adds a lambda to both the routers
      at either end and the optical switches (demonstrated at OFC).

  2.  The router signals the requirement/desire for an additional
      lambda to the adjacent optical switch which sets up a path.
      This is the overlay model.  It can be trivially implemented with
      MPLS by having the router send a loose source hop in the ERO
      allowing the switch to create the path or reject the request.

  3.  The router has enough information about the characteristics of
      the optical devices to compute the path and so it does so.  This
      is the peer model.

The way this might manifest itself is LSPs that might take an optical
path from A to C are going from A to B to C because A to C lambdas are
too full.  If so, then A could in principle request an additional
lambda, but in practice the means to signal this has not been defined.

Curtis

---

From: Yangguang Xu <[email-masked]>
Date: Thu, 23 Mar 2000 10:31:31 -0500

There have been many discussions about wavelength conversion. And we all agree
it is good. Can anyone tell me which OXC product (commercially announced)
doesn't support wavelength conversion?

Yangguang

---

From: Jagan Shantigram <[email-masked]>
Date: Thu, 23 Mar 2000 11:40:04 -0500

>      allowing the switch to create the path or reject the request.

Curtis,

Am trying to understand the model here. Does the overlay model
as you put above imply that the optical devices need to be mini-routers
in their own right? They have to be able to set up end-to-end optical
paths.. perhaps some kind of binding between the end-host IP address
and an addressing scheme for Optical devices.. ala ATM?
What does the overlay model entail?

>      the optical devices to compute the path and so it does so.  This

What does this model need.. a protocol for exchanging information
between the router and the optical device?

-jagan.

Jagannath Shantigram
Photonex Corporation

---

From: Curtis Villamizar <[email-masked]>
Date: Thu, 23 Mar 2000 13:54:55 -0500

In message <[email-masked]>, Jagan Shantigram wr
> What does the overlay model entail?

The optical devices run the same IGP (ISIS or OSPF) and use RSVP (or
CRLDP) in a manner similar to the ATM UNI setting up an SVC.

Alternately, the lambdas can be set statically and the edge router
simple advertises a Lambda-Switch Capable link ala
draft-kompella-mpls-optical-00.txt (if I understand their intent wrt
accommodating the overlay model).

I don't think draft-kompella-mpls-optical-00.txt has all the details
sufficiently ironed out for the case where the optical switch
advertises the availability of an optical link.  If it does, then the
details ar just not clear to me.  (Could be my careless reading).

> between the router and the optical device?

It needs a means to communicate OOB wrt the primary lightpath.  That
means would again be running the IGP and RSVP.  Based on reading the
draft-kompella-mpls-optical-00.txt draft, I'm not clear on how the
optical switch exchanges this information OOB although I would imagine
that it would be quite easy to maintian another interface (perhaps
even an electrical, though gig-E would do fine) between the router and
optical device in which the optical device advertises the optical
links.  The router on either end of an optical link, seeing or having
set up a Packet-Switch Capable link would then have to bring up an
RSVP adjacency over it, though I think it would not need an IGP
adjacency.  (I'm not clear on this last point.)

The availability of certain types of links (Packet-Switch Capable,
Lambda-Switch Capable, Fiber-Switch Capable) as defined in
draft-kompella-mpls-optical-00.txt would be advertised via RSVP.  I'm
not clear on whether the adjacent LSR should advertise a Forwarding
Adjacency PSC after RSVP comes up over a set of optical links (it
seems to be the intent) but maybe the authors can clarify the usage.

The ongoing discussion and the topic of the (way too numerous)
framework documents floating around has been what additional
information would be needed in order to provide adequate constraints
to set up optical paths, a particularly difficult problem for
transparent paths.

> >lambda, but in practice the means to signal this has not been defined.

btw- I exchanged some private email with one of the authors of
draft-kompella-mpls-optical.txt and owe them some detailed comments
(appologies to them for the delay, busy).  After some brief discussion
and after a second reading, the intent seems a lot more clear.  The
usage material is at the end so when reading the document from front
to back the intent is not clear until the end and then a second
reading is required.

Curtis

---

From: "Krishna Bala" <[email-masked]>
Date: Thu, 23 Mar 2000 14:48:34 -0500

Yangguang,
The optical switch from Corvis does not support wavelength conversion.

Krishna Bala
Tellium

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]]On Behalf Of Yangguang
> Xu
> Sent: Thursday, March 23, 2000 10:32 AM
> To: [email-masked]
> Subject: Re: Comments on draft-ip-optical-framework-00.txt
> 
> 
>

---

From: "Krishna Bala" <[email-masked]>
Date: Thu, 23 Mar 2000 14:58:38 -0500

Jagan,
There are several architectural models for IP over Optical Networks that
are emerging:

1. Peer Model
In this model the IP router is entirely aware of the details on the
underlying
optical network (topology information, wavelength and port usage and lamda
assignment).
It is able to control and manage entire end to end paths. In this model the
OXC is "agile but fat & dumb".
2. Overlay Model
The optical layer is "fat & dumb". The lamda connections between the IP
routers behave as if they were dedicated fibers between them. The IP routes
provision logical optical circuits over a fixed or at best a quasi-fixed
optical
layer.
3. Open Model
In this scenario the optical layer comprises of several "vendor/network
operator clouds"
that have well defined interfaces. For example, an Optical UNI can be used
to
interconnect the IP router to the OXC and the Optical NNI can be used to
connect
two optical network domains together. Here the optical layer is "fat, smart
and agile".

It is unclear at this time which of these models will prevail.

Krishna Bala
Tellium

> From: [email-masked] [mailto:[email-masked]]On Behalf Of Curtis
> Villamizar
> Sent: Thursday, March 23, 2000 1:55 PM
> To: Jagan Shantigram
> Cc: [email-masked]; Khaled Elsayed; [email-masked];
> [email-masked]

---

From: Yang Cao <[email-masked]>
Date: Thu, 23 Mar 2000 15:07:11 -0500

I try to clarify your definition, especially the difference between
your Overlay Model and Open Model.

So in your definition, there is no O-UNI or O-NNI in the Overlay Model,
and in this Overlay Model, optical layer is only manual provisioning based?

Thanks,
Yang

> Krishna Bala wrote:

---

From: Curtis Villamizar <[email-masked]>
Date: Fri, 24 Mar 2000 07:49:55 -0500

In message <[email-masked]>, Rana Pratap Sircar writes:
> Hi ,
> 
>     Can we also think of this possibility:-
> 
>     Space-based OXC overlay - In free Space , higher wavelengths can be used
> as well as a larger number of wavelengths ( since the limitations due to
> atmosphere [ scaterring and absorbtion etc.] and the limitation of glass
> attenuation and dispertion is reduced ). Ofcourse, it has the limitation of
> inherent difraction, and initial expenses of 3-4 Geostationary sattelites. So
> ,
> having an Optical Network  in space along with that on earth (fiber-based) fo
> r
> shorter ground based operations can be done. The data uplink and downlink to
> and from the GEO can be through microwave ( possibility of inverse
> multiplexing to increase the microwave data transmission ). This can give an
> option of mobility to these networks ( can be downlinked at any point on
> earth).
> 
>     Thanks & regards,
>     Rana

I don't know of any deployment of this or plans for deployment.  Its
probably not worth the MPLS WG effort to accommodate special needs
(which would more likely arise from the satellite uplinks than the
fiberless optical network in space).

If you periodically come back to earth keep us updated on progress.
:-)

Curtis

---

From: Rana Pratap Sircar <[email-masked]>
Date: Fri, 24 Mar 2000 09:40:33 +0100

Hi ,

inherent difraction, and initial expenses of 3-4 Geostationary sattelites. So,
having an Optical Network  in space along with that on earth (fiber-based) for

    Thanks & regards,
    Rana

---

From: "Krishna Bala" <[email-masked]>
Date: Fri, 24 Mar 2000 20:04:51 -0500

Yang,
The overlay model gives the impression that the optical layer is
static (or quasi static at best). It also gives the impression
that the IP layers needs to have N^2 connectivity in this case.

Krishna

> From: [email-masked] [mailto:[email-masked]]On Behalf Of Yang Cao
> Sent: Thursday, March 23, 2000 3:07 PM
> To: Krishna Bala
> Cc: [email-masked]; [email-masked]