The MPLS WG Archive

[Jay Wang <jawang@cosinecom.com>]

Title: RE: QoS and Labels: A question ??

>
> The EXP bits are for conveying DiffServ priority levels.  If
> you simply
> want to prioritize best-effort traffic, and your switches can suport
> E-LSPs, then this is the way to do it.
>
> If you need actual QoS guarantees, or if your switches only support
> L-LPSs, or if you want the two service levels to be routed
> independantly, then you need to create a separate LSP for each service
> level. 

No, I don't think this is the intention of draft-ietf-mpls-diff-ext(-07),
in which it was clearly stated that:

   "Within a given MPLS Diff-Serv domain, all the E-LSPs relying on the
   pre-configured mapping are capable of transporting the same common
   set of 8, or fewer, BAs. Each of those E-LSPs may actually transport
   this full set of BAs or any arbitrary subset of it."

That is, each E-LSP allows up to 8 combinations of <PSC, drop-precedence>.
With other mechanisms (in a Diffserv TCB) this would allow you to tansport
flows with different "QoS quarantees" using just one LSP (and fortunately so).

- Jay

> CR-LDP or RSVP-TE can be used for signalling the QoS
> requirements for the two LSPs.
>
> -- David
>