The MPLS WG Archive

[Shahram Davari <Shahram_Davari@pmc-sierra.com>]

Hi David,

To reiterate Jim's comments, I think you may be looking at Intserv concept. Diffserv can use both E-LSP and L-LSP to guarantee an aggregate QoS (not per microflow QoS). 

It is true that you could use Intserv with MPLS for a finer controlled QoS (per microflow QoS), and the result probably looks very similar to L-LSP, in which the QoS is derived from the Label context. But they are totally different solutions.


Yours,
-Shahram

P.S. you could also signal the meaning of EXP in E-LSP. This method is called Signaled E-LSP versus the Configured E-LSP.

> -----Original Message-----
> From: Jim Boyle [mailto:jboyle@Level3.net]
> Sent: Wednesday, January 24, 2001 11:13 AM
> To: David Charlap
> Cc: mpls@UU.NET
> Subject: Re: QoS and Labels: A question ??
> 
> 
> 
> 
> That is the difference between diffserv and intserv, I 
> believe.  Diffserv
> doesn't aim to give hard guarentees to individual flows.  
> Diffserv, and
> "E-LSPs", work.
> 
> Jim
> 
> 
> On Wed, 24 Jan 2001, David Charlap wrote:
> 
> > Bora Akyol wrote:
> > > 
> > > >>>>> "David" == David Charlap <david.charlap@marconi.com> writes:
> > > 
> > >     David> If you need actual QoS guarantees, or if your
> > >     David> switches only support L-LPSs, or if you want the two
> > >     David> service levels to be routed independantly, then you
> > >     David> need to create a separate LSP for each service level.
> > >     David> CR-LDP or RSVP-TE can be used for signalling the QoS
> > >     David> requirements for the two LSPs.
> > > 
> > > David
> > > 
> > > You are making assumptions about a particular switch
> > > architecture when you assert that you can not do "actual" QoS
> > > guarantees with E-LSPs. If you have a policer and a
> > > shaper/scheduler that can process the EXP bits as well as the
> > > label, then doing "actual" QoS is quite possible with
> > > E-LSPs.
> > > 
> > > Not only that, but you can map traffic destined to the same
> > > prefix to different EXP levels based either on Diffserv bits or
> > > on packet content. This also applies to VLAN tags.
> > 
> > The meaning of the EXP bits is not signalled.  It must be 
> preconfigured
> > network-wide.  And in order to be useful, they must be 
> identical across
> > the entire network.  Which limits you to 8 different service levels,
> > network-wide.
> > 
> > If you use the EXP bits to define a priority level and two flows are
> > both assigned that level, they will be queued in best-effort fashion
> > relative to each other.  There is no way to guarantee the individual
> > flows any particular level of service.  You can only guarantee the
> > aggregate of one class relative to another class.
> > 
> > Using L-LSPs, you can request a separate label, and a 
> separate resource
> > reservation for every flow, if needed.  This is the only way to
> > guarantee this level of service.  (Unless you're willing to 
> limit each
> > DS code point to a single flow, which is a ridiculous concept.)
> > 
> > E-LSPs are useful, no doubt about that.  But they can not 
> provide the
> > level of QoS necessary to make sure that a single specific 
> flow can be
> > guaranteed the resources it requires.
> > 
> > -- David
> > 
>