Subject: RE: Optical link bundling. Was Re: Draft Minutes From Pittsburgh

From: [email-masked]
Date: Thu, 19 Oct 2000 01:43:35 +0100

Hi Alex,

	You asked:
> > -       "server layer trails (in an OTN) = client layer links", and
> networks
> > operators *will* have to support multiple client layers for a very long
> > time...including some large BW servives directly off the L1 fabric.
> 
> Not sure I follow the logic here. Can you elaborate a bit.
> 
	This is a really important point.  It is a fundamental
characteristic of a layered network architecture.  It (and other functional
modelling concepts of layered networks) are more fully described in G.805
(ITU) and also in some text books like:
	-	'Global Information Networking' Varma et al. Artech
	-	Broadband Networking' Reid & Sexton. Artech

	In essence, if I want to create a topology at some arbitrary layer
(in some technology) I can do this by connecting boxes with links to form
some sort of graph......this is the simplistic box diagram approach.  But
each of these links can be provided by a lower layer network, which is
itself a topology of boxes and links.  And this process recurses until we
hit the 'duct'....which is the lowest layer network of all (and which, BTW,
determines a bound on the inherited availability performance of all higher
layers).

	Hence, a link connection between 2 nodes at layer N is a small
segment of a large trail at layer N.  The trail end points in layer N are
closely bound to the access points which are the addressable entities of
layer N, ie the entities between which we need to determine routing between
at layer N.  But *each* of the link connections at layer N will generally be
provided by a trail at Layer N-1.  Hence, the addressable access points of
the trail at layer N-1 are clearly not the same as those at Layer N.  I have
tried to show this nested inter-layer trail relationship below (0 = trail
termination point/addressable location of layer network, (X) = switching
point in layer network):

	<----------------------------------Trail at layer
N------------------------>
	
0-----------(X)---------------(X)-----------------------(X)----------------0
	                                        /   <--------------------->
\
	                                     /  link connection at N      \
	                                   /
\
	
0--------(X)---------(X)-----------0
	                                  	<----trail at
N-1--------------->
							           /
\
	                                            /                      \
	                                          /
\
	                                         0  -----(X)----(X)----0
	                                         <---trails at N-2----->
	                                                    /           \
	                                                  /                \
	                                                    etc to duct

	BTW nested LSPs also fit this model.......but this has not been
recognised yet.

	Neil

---

From: Alex Zinin <[email-masked]>
Date: Wed, 18 Oct 2000 19:56:32 -0700

Neil,

> characteristic of a layered network architecture.

Got it. I didn't realize what layers you meant.

>         BTW nested LSPs also fit this model.......but this has not been

It has been, actually.
The forwarding adjacencies, LSP hierarchy and generalized MPLS are
the mechanism to represent LSPs as links for higher layers,
perform signaling of different types of LSPs and LSP nesting.

Alex.