RE: More comments/questions on DS-TE solution draft

[Jim Boyle <jboyle@pdnets.com>]

On Mon, 10 Jun 2002, Francois Le Faucheur wrote:

> Hi Sanjaya,
>
....
>
> >How your are planning to address situations where one
> >of the interface in the LSR, connects to a legacy TE
> >LSR and the other to a LSR that supports DS-TE ?
>
> I think this could work under the following assumption:
>
> the TE-Class mapping in the DS-TE domain must be such that:
>          - a TE-class exist for CT0 for every preemption priority actually
> used in the TE domain
>          - the index for each of these TE-classes is equal to the
> preemption priority

sounds good.

...

>
> Coming back in more details to your "hybrid" LSR case (lets' call it LSR1)
>          - there is a single TE-class mapping (it is a LSR-level
> parameter), say for example
>                  i       CT    Premp
>              ========================
>                  0 <-->  1       0
>                 1 <-->  1       1
>                  2 <-->  0       2
>          3 <-->  0       3
>                  rest <--> unused
>          - interface 1 to DS-TE LSR (LSR2) is configured with say BC0 and
> BC1 (those are link-level parameters)
>          - interface 2 to legacy TE LSR (LSR0) is configured with BC0 only
>
> LSR0 will only initiates regular TE tunnels with preemption 2 and 3, therefore:
>          - for interface 1 and interface 2, it needs to get the correct
> unreserved bw for CT0/premption 2 (resp 3) in the 3rd (resp. 4th) position
> in the "Unreserved Bw" sub-TLV of the IGP. This will be the case since this
> corresponds to the TE-Class mapping of LSR1.
>          - it will do nothing with all the other values advertised by the
> IGP in the Unreserved Bw sub-TLV. So the fact that , for example, the first
> value advertised by LSR1 for interface 2 actually relates to CT1 will not
> adversely affect LSR0.
>
> LSR0 needs to get the old "Max Reservable bw" for all links. Currently the
> DS-TE-PROTO draft says that if multiple CTs are used, only the new
> "Bandwidth Constraint" sub-TLV is used. I guess we should change
> that text

well, it doesn't quite say that, but it seems to be heading in that
direction.  That object is supposed to be optional, for those that
prefer efficiency over verbosity.  We should revisit the text to make
the optionality clear.  E.g. the line "When DS-TE is deployed and
multiple CTs are used, the new Bandwidth Constraints sub-TLV is
used" should read "may be used".  (in fact no reason it can't be used
when there is only BC0 - though I suppose that's totally pointless.

> to optionnaly allow advertisement of both the new Bandwidth Constraints"
> sub-TLV and the old "Max Reservable Bw" in case there may be some
> non-DSTE-capable LSR in the network. right?
>

.....

> I guess we may add some text saying that a DS-TE LSR should only make use
> of Unreserved Bw [i] if there is a BC advertsied for the CT of that
> TE-class on the corresponding link. right ?

Hmmm.  I think we're heading towards option (2) of the thread in:

http://ops.ietf.org/lists/te-wg/te-wg.2002/msg00017.html

The BC sub-object should remain optional.  I like the philosophy of
just checking the reservable bandwidth at the appropriate priority or
te-class (for standard and dste routers respectively), w/o *having* to
do all sorts of other checks.

regards,

Jim

>
> If you agree with these few changes to ensure interoperability, they could
> be incorporated in the next rev.
>
> Thanks for raising this point.
>
> Francois
>