Subject: Question on MPLS E_LSP

From: Young Lee <[email-masked]>
Date: Tue, 14 Nov 2000 12:29:55 -0600

I am wondering if any networks are implementing MPLS E-LSP with one LSP
supporting more than one class within?  If so, what are the advatages of
this implementation over having only one class for an LSP?

One advantage I can think of is the scaling by putting multiple classes into
one LSP.  But, is it feasible to support bandwidth gurantee for each class
with this implementation?  When an application requires a strict bandwidth
gurantee for each service (say, 10Mbps for video and 5 Mbps for data), can
MPLS E-LSP support this?   Also, how would the MPLS-TE attributes such as
adaptability and resilience be applicable to multiple classes within LSP?

Young Lee
Iris Labs

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From: Francois Le Faucheur <[email-masked]>
Date: Fri, 17 Nov 2000 17:38:05 +0100

Young,

>this implementation over having only one class for an LSP?

It is VERY simple. You stay with one single LSP (just as if you were not
using Diff-Serv) and you set-up/signal E-LSPs with absolutely no change to
the signaling (just as if you were not using Diff-Serv).

If you want to support the whole of Diff-Serv and nothing but Diff-Serv,
this is definitely the simplest way.

>MPLS E-LSP support this?   

Well, if you want to offer strict point-to-point QoS commitments to
differnet classes then you may need multiple LSPs. But note that (assuming
you have no more than 8 Behavior Aggregates to support) you still have a
choice:
	- you can set-up multiple L-LSPs (then by definition they transport one
class each)
	- you can set-up multiple E-LSPs and only send one class on each. 
In both cases you may perform constraint based routing with constraints
which depend on the transported class (see draft-ietf-mpls-diff-te-00.txt
which discuss Diff-SErv aware Traffic Engineering)

>Also, how would the MPLS-TE attributes such as

yes, if you want to apply different resiliency policy to differnet classes
you woudl need multiple LSPs. Again you have the choice between multiple
E-LSPs or multiple L-LSPs.

Cheers

Francois