Re: make-before-break in Gmpls

[Dimitri.Papadimitriou@alcatel.be]

hi,

i think this issue concerning "se style" has been discussed
some time ago but let's try here to give a bit more details,
lsp's in gmpls are control plane entities mapping data plane
ones, merging here does get sense if and only if the data
plane would deliver the same capability, since the soft-
provisioning that we can expect in shared meshed restoration
is purely a control plane driven mechanism the corresponding
entity doesn't occur at the data plane level and in particular
for tdm, lsc and fsc lsp's, once committed you find out the 
ff style as used today, as such there is no today something
like you seem to assume as setup of an lsp "split" it when 
a recovery lsp is needed and then "merge" it back when the
recovery lsp find back the working lsp path, then next even
if the methods that are under definition may be thought as
similar to the frr ones, the following for instance wouldn't
strictly apply (see fast-reroute):

"When using the sender-template-specific approach, the protected
LSPs and the backup paths SHOULD use the Shared Explicit (SE)
style. This allows bandwidth sharing between multiple backup
paths. The backup paths and the protected LSP MAY be merged by the
Detour Merge Points, when the ERO from the MP to the egress is the
same on each LSP to be merged, as specified in [RSVP-TE]."

this because for non-packet networks do soft-provisioning 
means let the capability to share the bandwidth on a control
plane view of the resource basis otherwise just provision 
it (commit it) since having a dedicated soft-provisioning 
on a per lsp basis just means be dedicated at the data plane 
level (if we assume a consistent usage of the mechanisms), 
and on the other side have merging (not multiplexing) of 
lsc or tdm at the data plane level is impossible (afaik) 
thus the fact that one knows that the requested lsp is for 
recovery purposes (link protection tlv s bit set) and its 
resources have to allocated within a pool but not committed 
(ie reserved) something which is needed in any case, do
the job here.  

hope this clarifies a bit,
- dimitri.

Manoj Agiwal wrote:
> 
> Hi ,
>          The gmpls architecture documents says
> "GMPLS does not add anything new. Elegant re-routing is possible with the
> concept of "make-before-break" whereby an old path is still used while a new
> path is set up by avoiding double reservation of resources. Then, the node
> performing the re-routing can swap on the new path and close the old path.
> This feature is supported with RSVP-TE (using shared explicit filters) and
> CR-LDP (using the action indicator flag).
>           Will this feature will hold good for optical networks as well ,
> where we have TDM , LSC  LSPs. This would require use of
>      SE style in optical networks . Does signaling has to take care of not
> reserving extra resources ( bandwidth / time slot )
>     across the common path of the two LSPs , what will happen at the nodes
> where the two routes diverge and converge .
>     Is it expected that the signal will get multicast to both the routes ,
> and at the node where the route converge the signal
>     is selected from the better of the two paths till the rerouted LSP is
> torn down .
> Regards,
> Manoj

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Papadimitriou Dimitri 
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