Subject: Re: [Isis-wg] DDRP (was doubts)

From: Jonathan Sadler <[email-masked]>
Date: Fri, 27 Sep 2002 19:51:50 -0500

Mike -

The 30,000 node issue is not about the DCN, or about IP address
utilization -- instead it describes the complexity of the graph that
the ASON routing will be done over.  Since in ASON each node is a
switching point, it is basically an IS.  For the simplest topologies,
the number of links will be the number of nodes minus one.  And the
transport networks are certainly far from simple -- they're more like
a sparse mesh than a string or a hub/spoke topology.  Therefore
reducing graph complexity is important to keeping route calculation
times reasonable.  Use of hierarchical calculation is one way of
accomplishing this.

When hierarchical calculation is used, the next question is what
should the hierarchical "chunks" be.  While it may be possible to
run an area with 600 or so ISes in it, the network topology may be
such that creating a 600 node area is not practical, not to mention
the fact it doesn't provide any growth room.  Instead, it is better
to look at how the network is organized.  Since many Telco service
providers organize their networks and operations staffs along the
lines of metro, regional, national and international networks, the
best deliniation of an area may be similar.  For example, the Chicago
Metro may be one area, with Metro Indianapolis as another, and Metro
Detroit as a third.  These areas would then be contained in the
Upper-Midwest area.  In turn, the Upper-Midwest area as well as,
say, the BosWash area and others would be contained within the North
America network.  This would be contained along with the Europe
network (and others) in the "world" network.

Given this design, a 4-level hierarchical routing protocol is
necessary.  And we havn't even started adding levels to deal with
the interconnection points between service providers.

Jonathan Sadler

Mike Truskowski wrote:
> 
> And to complete... you wouldn't need a multi-layer heirarchy greater
> then 2.
> 
> Mike
> 
> > Jonathan,
> >
> > My understanding was that DDRP is nothing more than a simple way of flooding TE type information around a cloud.  More specifically it uses the OSPF flooding mechanism, without the requirement for building an IP forwarding table.
> >
> > Basically the layers of hierarchy are provided having multiple clouds which do not interact with each other, other than that the TE information "somehow" gets passed from one cloud into another.  My understanding was that the "somehow", which is actually the unique point, is not yet defined.
> >
> > If I am right then one could use IS-IS as a flooding mechanism instead (or any other).  The TE stuff could still be delivered to the edge of the cloud and passed onto the next (somehow), but the IS-IS LSPs wouldn't.  You wouldn't need 30,000 IP addresses either.
> >
> > Have I got it about right ?
> >
> > Philip
> >
> >
> >
> >
> > ----- Original Message -----
> > From: Jonathan Sadler <[email-masked]>
> > Date: Thu, 26 Sep 2002 15:20:18 -0500
> > To: Jeff Parker <[email-masked]>
> > Subject: Re: [Isis-wg] doubts
> >
> >
> > > Jeff -
> > >
> > > Jeff Parker wrote:
> > > > > The biggest probably is the need to support
> > > > > Multi-Level hierarchies with a depth greater
> > > > > than 2.
> > > >
> > > >         While I don't want to start a food fight
> > > > here, can you help me understand why we need
> > > > additional levels?  I have heard people mutter
> > > > things about this for years, but I haven't
> > > > really understood the point yet.
> > >
> > > The main rationale has to do with the way that Telecom Service Providers
> > > organize their operations staffs, as well as their networks, and the
> > > size of those networks.  Many operate separate groups that individually
> > > focus on Metro, Regional, National, and International networks.
> > > Consequently, there is natural summarization in the network designs.
> > > Couple this with aggregate SONET/SDH node counts of >30,000 (!) nodes
> > > and you can see why they find hierarchy for ASON routing desireable.
> > >
> > > Jonathan Sadler
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---

From: Jeff Learman <[email-masked]>
Date: Sat, 28 Sep 2002 17:40:53 -0400

>the interconnection points between service providers.

Those should definitely be inter-domain routing protocols, not intra-domain.
And while I don't doubt that there's a potential benefit to multi-level
IS-IS, it also may make the most sense to use inter-domain routing
between high-level regions within a single service provider (based
on administrative autonomy).

If you're serious about multi-level IS-IS, I know that Radia Perlman
had an idea of how to add this a couple years back, but there wasn't
enough interest in it in the industry for her to dig into it very far.

My understanding, drawn almost entirely from responses on this mail
list, is that very few networks even run 2-level IS-IS.  I realize that
this is based on ISP networks, as opposed to embedded telecom
management networks.  In support of your arguments, though, I understand
that in embedded telecom management networks, it isn't possible to
simply "build a manageable network" like it is when the routing protocol
is supporting the payload traffic.  Instead, there are a number of                                                      
complicated driving principles in the network design, and the foremost
are those concerning the payload network topology -- the embedded
management network topology considerations are secondary.  Most router
jocks are simply not used to this kind of situation and it's
understandable that they have difficulty envisioning the need for
the complexity.  "Why in the heck would you design a routing network
using cascading rings?  Why are you using such underpowered routers?"  ;)

Regards,
Jeff

Regards,
Jeff