[Nsi-wg] Conversation about ITU concepts with Ciena folks

[John Vollbrecht]

Jeroen van der Ham, Guy Roberts and myself had a conversation with  
Lyndon Ong, George Newsome and Rajender Razdan of Ciena about ITU  
networking recommendations.  This was extremely helpful, and I thank  
the Ciena folks very much for their time and help.

The following notes are put together by Jeroen and myself - please  
feel free to add or correct or question.

We spend the first part of the meeting going over slides (see  
attachnment below) describing NSI concepts in G.800 terms.  It is  
worth noting that George described the evolution of the  
recommendations as G.805 describing connection oriented networks, G. 
809 attempting to extent that to connectionless networks, and then G. 
800 which combines both.  He also commented that the way that G.800  
came to be is that "G.805 was observed to be insufficient for  
describing packet-switched networks (especially ethernet).  Updating a  
standard is hard, hence a new standard."   So using G.800 concepts is  
what is done in the slides and in discussions we have had earlier on  
the mailing list.

G.8080 unfortunately still uses G.805 terminology, and adds some more  
- but is in the process of being updated/reviewed.  G.8080 is also  
called ASON.

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On slide 2 it was remarked that it uses the term Subnet. This really  
is an abbreviation of Subnetwork, which is okay.  It is probably  
better to use the full word subnetwork to distinguish it from IP  
subnets.
On slide 3 and slide 6 we found that the ITU uses Link responder and  
Subnetwork responder as terms for the agents.

On slide 5 we had a long discussion on terminology.
There is a distinction between a Layer Network and a Routing Area,  
having to do with whether you could see the Link end or not (not  
completely sure?)  In general George says that he thinks of them as  
basically the same.

On slide 5 there was a discussion on the difference between a SNPP  
(subnetwork point pool) and a port.  A SNPP is an ASON concept that is  
essentially the same as a link port except that a  port might have  
multiple SNPPs.  The SNPP is what is used for routing.
The ASON concepts are named slightly differently than G.800.  Link  
ports in 800 are Subnetwork ports (SNP) in 8080.  George says that in  
casual conversation both are called ports.

More on slide 5 Subnetwork is what the ITU calls it, but usually  
Network is used anyway when talking about it.  NSI will likely switch  
to use the term Network for the concept that G.800 calls subnetwork.

The distinction between Port and Point in G.800 is not helpful and for  
most intended purposes you can just use Port (for what G.800 calls a  
Point).  The Forwarding Port seems to be fine.  Forwarding point is  
where segments from different resources connect.  In G.8080

Segment also seems okay, and is used in G.8080 for the same concept as  
it is used for in NSI - otherwise known as link connection  and  
subnetwork connection in G.800.
AccessPort is okay.  Note that G.800 makes a clear distinction between  
a network connection which goes across a network, and a client  
connection which goes between clients (where clients connect to  
network).

We also talked about document on multiple layers.  The doc is attached
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The first figure in the doc seemed a normal way of describing a link  
on one layer being implemented on a different layer.  George wanted to  
understand the second figure better - it shows that a network  
connection at one layer (ethernet layer) may include segments from  
another layer (SONET layer), and that there may be no link at the  
ethernet layer between the ethernet subnetworks.

George said this was an interesting problem and that he had proposed  
the concept of transitional links to between ports at different layers  
to describe this concept.   I am not sure I understand this  
completely, but I believe the idea is that doing this allows topology  
from both layers to be considered in pathfinding.  This needs more  
thinking - at least on my part.

George sent a number of documents that describe transitional links and  
other concepts.  I am in the process of reading these still.

There were some concepts indicating that GMPLS was not as good at  
describing multi-layer capabilities as G.800 (and possibly NML).  I  
don't really understand precisely why.

Thanks very much to all who participated.