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?