Subject: Re: draft-ietf-mpls-rsvp-lsp-tunnel-08.txt

From: Anouk Rocher <[email-masked]>
Date: Thu, 12 Jul 2001 16:36:52 -0400

David,

Once again thanks for your very helpful email

[cut]
>These constraints all serve to generate an explicit route.  This ERO may
>be computed by the router, by manual configuration, or by some
>standalone management server.  Once the ERO is computed, RSVP doesn't
>have to care about the constraints that were used to compute it.
>
>-- David

I didn't state it clearly enough in either of my messages - yes I do
understand that typically paths based on costraints are calculated
at the LERs (not considering the management station case here) and
the path along with the path requirements fed into a signalling protocol
-  either RSVP/TE or CRLDP.

I was mostly trying to figure out how the calculate requirements are
mapped into the various RSVP objects . Specifically if the ingress LER
calculates (say) a 10Mbps path through a network and specified all the
hops to pass through via ERO, what else should it do to tell the nodes
along the path that 10Mpbs should be given to the LSP being set up.

From your explanation, I understand that first the ingress LER sends
out a TSPEC saying that 10Mps is requested along with an ADSPEC
specifiying the type of service (say controlled load). The Egress
LER returns a FLOWSPEC. Each node on the return path then begins to
use the parameters in the FLOWSPEC to provide the service originally 
requested by the ingress and confirmed by the egress. 

First, Derived from a re-glance at the documents and your email again,
is this flow of events in the ballpark even if not exact?

Second, is it legal to for an intermediate LSR to use the TSPEC and ADSPEC
parameters on the forward path rather than the reverse path? I was thinking
of this in order to not lose available resources during the forward path
which may not be around when the messages start coming back from the
egress.

Anouk

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---

From: David Charlap <[email-masked]>
Date: Thu, 12 Jul 2001 16:48:11 -0400

Anouk Rocher wrote:
> mapped into the various RSVP objects . Specifically if the ingress
> LER calculates (say) a 10Mbps path through a network and specified
> all the hops to pass through via ERO, what else should it do to tell
> the nodes along the path that 10Mpbs should be given to the LSP
> being set up.
> 
> First, Derived from a re-glance at the documents and your email
> again, is this flow of events in the ballpark even if not exact?

Yes, your description is correct.

> Second, is it legal to for an intermediate LSR to use the TSPEC and
> ADSPEC parameters on the forward path rather than the reverse path?
> I was thinking of this in order to not lose available resources
> during the forward path which may not be around when the messages
> start coming back from the egress.

It isn't forbidden to do so, but it changes the dynamics of the
protocol.  It may solve some kinds of problems, but it will create other
problems.

There was a rather long discussion on this not too long ago, which I'd
rather not repeat.  If you search the mailing list archive, you
shouldn't have any problem finding it.

-- David

---

From: George Swallow <[email-masked]>
Date: Thu, 12 Jul 2001 17:04:06 -0400

> which may not be around when the messages start coming back from the

That what our implementation does.  We consider it a matter of policy
not to forward a Path message if the T-SPEC can't be met.  We also set
the resources aside until either the Path times out or a RESV message
makes the formal reservation.

...George

==================================================================
George Swallow       Cisco Systems                   (978) 244-8143
                     250 Apollo Drive
                     Chelmsford, Ma 01824