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

[Jerry Sobieski]

John Vollbrecht wrote:
> comment below
> On Sep 7, 2009, at 5:45 AM, Guy Roberts wrote:
>
>
> If path computation is the only proposed use for transitional links  
> then I am not sure that we need to use the concept in NML, or are we  
> proposing another use that I have missed?
>
>   
>
> I think that transitional link is a way of flattening topology where  
> it is possible to do adaptations between layers.  It requires that a  
> device be represented at both layers and have a link between layers  
> with a specific adaptation.  When doing pathfinding using such links  
> one must be sure adaptations and deadaptations match such that the  
> client info is passed through.
>
> I think this concept is highly useful for describing a "routing area"  
> over which pathfinding can be done.  We should consider this relative  
> to other methods of pathfinding which seem more difficult to use in  
> practice.
>
> John
>
>
>   
Hmmm...I guess I am confused.   I thought transitional links *were* 
adaptation components of the topology (and vice versa).   A selected 
path that transited/transitioned an adaptation componet had to configure 
that adaptation at provisioning time;   I think though, whatever you 
call it or where ever it is in the topology, transitional links / 
adaptation components function differently in two different situations:  
a) Encapsulation, and b) stitching.   The former, is a "vertical" 
transition where the upper layer protocol is tunneled in its entirety 
through the lower layer protocol (ala IP/Ethernet, or Ethernet/sonet 
(via GFP adaptation) ) and must have a matching decapsulation function 
at the egress, and the latter is more "horizontal" transition where the 
current transport protocol is stripped in its entirety leaving only the 
user data payload which is then placed in the next transport protocol 
for forwarding (the stitching adaptation does not require a matching 
function at its egress point - only whatever it needs for the next 
stage).   Does this jive with the discussion and other papers on these 
concepts?

Jerry
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