on draft-awduche-ipo-gmpls-signaling-applicability-00.txt

hi dan, adrian, all

in the above mentioned document section 6.2.1, you discuss
the applicability of the currently available label selection
schemes with respect to the LSP directionality (uni vs bi)

As described in GMPLS RSVP-TE signaling, for bi-directional
LSP, an upstream label has to be selected at each hop before 
the Path message is transmitted to the next-hop. 

On the other hand, a label set that includes one or more labels 
for the downstream path is carried by Path message and the Resv 
message selects a label at each node (upstream direction).

in brief two mechanisms are currently considered for label 
selection:
- Unidirectional LSP: (downstream) label set
- Bi-directional LSP: (downstream) label set and upstream label

with the following remark: bi-directional lsp could be made up
two uni-directional lsps (with all the complexity you have 
mentioned) and the suggested label allows for a commodity
(as such it could be in the future integrated within the label
set by simply adding a flag since it has a restricted semantic
with respect to the downstream label set)

taking a look at the following i-d: 
http://www.ietf.org/internet-drafts/draft-oki-ccamp-upstream-labelset-00.txt
          
an improvement is discussed to extend the upstream label to an 
upstream label set, thus one would have the following symmetric 
approach: 
- Unidirectional selection scheme: (downstream) label set
- Bi-directional selection scheme: (downstream) label set and upstream
label set

this seems to be aligned with what you have referred to as a
"symmetric" approach of the label selection problem, i don't
know how deep you plan to go in these applicability statements
but it seems worth spending some text on this issue (which
is by the way unique to all-optical networks ie when signal
is not electrically terminated at each hop)

thanks,
- dimitri.

-- 
Papadimitriou Dimitri 
E-mail : [email protected] 
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