Re: I-D ACTION:draft-ayyangar-ccamp-lsp-stitching-00.txt

[Arthi Ayyangar <arthi@juniper.net>]

Igor, Dimitri,


> > which flexibility are we expecting here, this "segment" can accommodate
> > exactly one incoming request -
>
> IB>> Disagree - the segment could be a component link within a bundle. In
> this case stitching FA TE link may accomodate multiple LSPs
>
>  additionally only nodes part of the same
> > area can make use of this advertisement -
AA-----> I agree with Igor...one of the reasons you advertise an FA is
to attract traffic over that FA, note that it is advertised with
TE metric = (TE metric of FA LSP path - 1) ..... I would think this would
also be the reason to advertise an LSP segment, IF this is desired. Again,
note that this decision is completely local to the node originating the
LSP segment and would be dictated by some policy.

> IB>> Who said that sticthing segments must necessarily terminate on domain
> borders? There could be multiple reasons why a network operator could
> pre-provision (dynamically or statically) LSP segments inside his network
> and advertise them (as bundles or individually) as TE links to be used for
> specific TE purposes.
AA----------> Agreed.

thanks,
-arthi

> IB>> See my comment above. I might want to use statically provisioned
> segments. I might want to use nodes that do not have proper signaling
> software.
> For instance, recall the discussions on P2MP and how we want use legacy LSRs
> to be part of P2MP tunnels
AA-------> Absolutely.

> >
> > in case of classical FA-LSP it makes sense to advertize the FA link
> > because it represents a lower region LSP (with usually a given ratio of
> > unreserved bandwidth that makes worth advertizing the FA link) but in
> > case of a segment i do have some difficulties to excatly see where this
> > flexibility would deliver ?
>
> IB>> Again, if you imagine that several parallel sticthing segments are
> advertised as as single FA, how it would be different from the bandwidth
> usage point of view compared to advertising lower layer FA ? In fact it
> would be even more useful, because in case of lower layer FA you need also
> to advertise termination/adaptation capabilities, while in case of stitching
> FA no addaptation is required.
>
> Igor
> >
> > thanks,
> > - dimitri.
> >
> > >>thanks,
> > >>- dimitri.
> > >>
> > >>
> > >>>>>a more technical point is related to the definition of an FA LSP
> which
> > >>>>>per LSP-Hierarchy mandates crossing LSP region border: the head-end
> and
> > >>>>>tail-end switching capability represent the SC of the resulting TE
> link
> > >>>>>while intermediate node terminates the SC corr. to the switching type
> > >
> > > of
> > >
> > >>>>>the FA-LSP (e.g. creation of a [PSC-1,PSC-1] link throughout a PSC-2
> > >>>>>capable network with first and last link being [PSC-1,PSC-2] and
> > >>>>>[PSC-2,PSC-1], resp.), while in the LSP segment case we would have
> now
> > >>>>>the creation of a [PSC-1,PSC-1] link with first and last link being
> > >>>>>[PSC-1,PSC-1] and [PSC-1,PSC-1], resp. so there is no region border
> > >>>>>crossing anymore - so here the question is about definition and
> > >>>>>detailing the triggers
> > >>>>
> > >>>>AA--------> As far as trigger for setting up an LSP segment is
> > >
> > > concerned,
> > >
> > >>>>I agree that there is no longer the notion of "crossing region
> > >>>>boundaries". I realize that the document doesn't discuss this,
> > >
> > > especially
> > >
> > >>>>given that we are doing other comparisons with FA LSPs. So, I will add
> > >>>>this discussion in the next revision. I think in case of LSP segment
> the
> > >>>>trigger for LSP segment setup would come from a) successful switching
> > >
> > > type
> > >
> > >>>>and switching capability match and b) some local policy on the node
> > >
> > > which
> > >
> > >>>>dictates the setting up of an LSP segment.
> > >>>>
> > >>>
> > >>>
> > >>>IB>> I have a comment here. LSP-Hierarchy is not a Bible and could be
> > >>>challenged in many ways. FA LSP is, generally speaking, created on a
> > >
> > > layer
> > >
> > >>>boundary rather than on region boundary: nothing prevents creating a
> VC4
> > >
> > > FA
> > >
> > >>>LSP that starts and stops in the middle of TDM region to carry several
> > >
> > > VC12
> > >
> > >>>LSPs. Furthermore, stitching FA is a special case of FA when it is used
> > >
> > > by
> > >
> > >>>LSPs of the same layer as one where the FA-LSP was created. As for
> > >
> > > triggers,
> > >
> > >>>there could be multiple ones for setting up/tearing down stitching
> > >
> > > FA-LSPs:
> > >
> > >>>configuration, receiving setup request for inter-domain LSP, other
> > >
> > > policies.
> > >
> > >>>Igor
> > >>>
> > >>>
> > >>>
> > >>>
> > >>>
> > >>>>More on a) later.
> > >>>>
> > >>>>thanks,
> > >>>>-arthi
> > >>>>
> > >>>
> > >>>
> > >>>
> > >>>
> > >>>.
> > >>>
> > >>
> > >
> > >
> > > .
> > >
> >
>