The MPLS WG Archive

[Daniel Awduche <awduche@UU.NET>]

Hansen,

Online LSP path computation is the preferred operational model in many
contexts -- for many good reasons.  Obviously, service providers
have the option to activate these aspects according to their
circumstance and needs...

As a simple rule of thumb, in networks with adequate capacity, online
constraint-based routing should suffice for LSP path placement. In
relatively under-capacitated networks, however, significant 
offline effort may be required to squeeze additional utility from the
infrastructure.

Cheers,
/Dan

On Fri, Apr 21, 2000 at 11:06:08PM -0400, HANSEN CHAN wrote:
> Dan,
> 
> I agree that most MPLS implementations perform LSP path computations online. But I
> always thought the working LSPs deployed in the networks are still computed
> offline. You only use online computations when you're re-routing/repairing the LSPs
> around some failure. Is my understanding correct?
> 
> Cheers,
> Hansen
> 
> Daniel Awduche wrote:
> 
> > Hansen,
> >
> > Yes, many (perhaps most) contemporary implementations perform
> > LSP path computations online. This is a mandatory requirement
> > in some operational contexts. It's also possible to augment
> > the online system with offline software tools.
> >
> > Cheers,
> > /Dan
> >
> > On Thu, Apr 20, 2000 at 06:04:13PM -0400, HANSEN CHAN wrote:
> > > Dan,
> > >
> > > To make sure I understand. Do you mean the path of LSPs is computed on the
> > > node, not by software tools?
> > >
> > > Thanks,
> > > Hansen
> > >
> > > Daniel Awduche wrote:
> > >
> > > > Actually, the original assertion/generalization is false
> > > > (i.e. that "LSPs in today's MPLS network are usually computed
> > > > off-node").
> > > >
> > > > Cheers,
> > > > /Dan
> > > >
> > > > On Thu, Apr 20, 2000 at 02:08:22PM -0400, Anoop Ghanwani wrote:
> > > > >
> > > > >
> > > > > > I am trying to understanding the use of TE extension of IGP in a MPLS
> > > > > > network. From my understanding, you need TE extension when you're doing
> > > > > > on-node path computation. However, since LSPs in today's MPLS network
> > > > >                                                    ^^^^^^^^^^^^^^^^^^^^
> > > > >
> > > > > We're hoping it won't stay that way forever because it's limiting
> > > > > to have to rely on offline tools for all traffic engineering :-)
> > > > >
> > > > > That means that traffic engineering would need to be more dynamic,
> > > > > and the routers would play a more active role in determining paths
> > > > > and possibly doing network optimization.  Hence the IGP extensions.
> > > > >
> > > > > > are usually computed off-node (in software tool), why would the use of
> > > > > > TE extension be critical?
> > > > > >
> > > > > > Appreciate if someone can shed some light on this question.
> > > > >