The MPLS WG Archive

["HANSEN CHAN" <hchan@newbridge.com>]

Dan,

> >
> > I just want to add one other point. When a network operator wants to use a
> > small set of LSPs to remove a few hot spots in the network assuming all
> > other links having satisfactory performance, an offline tool may be the
> > preferred way to identify which traffic trunks that contribute to those
> > congestion points should be re-routed away from those hot spots, and then
> > figure out what the new non-shortest path should be, and leave all the rest
> > of the traffic on its normal shortest path.
>
> Yes, if specific pathologies exist (e.g. hot-spots) within
> the network, then intervention is usually necessary to
> address the situation. In such cases, analysis can be
> conducted offline to diagnose the problem and prescribe
> an appropriate course of action, which may involve defining
> or identifying LSPs to route/re-route through alternative
> paths with adequate capacity. If frequent intervention
> is warranted, then perhaps there are more fundamental
> issues at play which demand a stronger solution, e.g.,
> augment capacity, review and amend the operational
> process models, etc.
>
> >
> > As far as I know, all the online LSP path computation algorithms provided by
> > the vendors are not capable of taking the normal IP traffic into account
> > since the algorithms only see the bandwidth requirements from traffic on
> > LSPs. If one has to use the online LSP path computation algorithm, he/she
> > needs to use some offline tool to figure out the aggregate bandwidth
> > requirement by the normal IP traffic on each link (excluding the traffic
> > trunks that will be routed via LSPs), substract that from the total
> > available bandwidth for that link, and make that the new available bandwidth
> > for the online LSP path computation algorithm to use.
>
> Yes, if "normal IP traffic" (traffic that do not traverse through
> LSPs) constitute a reasonable proportion of the workload through
> an MPLS domain, then online constraint-based routing becomes
> less effective and additional offline effort may be required.
> The operational model can also be amended to reduce the amount
> of effort required...

You raise an interesting question. There're two scenarios you described:

Scenario A: networks of "normal IP traffic" with a reasonable proportion of the
workload
Scenario B: networks of "normal IP traffic" with minimal proportion of the
workload

Offline computation seems to be the preferred choice in scenario A while online
computation appears to be the preferred choice in scenario B, from the e-mail
discussion so far.

Then my question is, which scenario will prevail in the "next generation network"
(sorry for not able find a better word)? Would IP traffic on LSP be the norm or
"normal IP traffic" be the norm?

Cheers,
Hansen