The MPLS WG Archive

[Vishal M <vishal_study@yahoo.com>]

Perhaps I should re-phrase my question:

The packet is classified by the ingress LER and EXP
bits are marked. IP packet is prefixed with MPLS shim
header and forwarded in the MPLS cloud.

Questions:
==========
Why do we need to propagate (or signal) EXP<=>PHB
mapping to the core-LSRs ?

Why can't the core LSRs do the scheduling just based
on the EXP bits ? What additional functionality does
the PHBID serve at the core-LSRs?

Could someone pls help...

Thanks,
Vishal.

--- Vishal M <vishal_study@yahoo.com> wrote:
> 
> Hi,
> 
> This is quite a basic question on on MPLS Support of
> Diff Serv (draft-ietf-mpls-diff-ext-09.txt).
> 
> The draft talks about having EXP<=>PHB mappings on
> all
> the LSRs a LSP passes through.
> 
> I understand the need for having PSC mapping to EXP
> on
> the ingress LER. i.e. an ingress LER that converts
> IP
> to MPLS would have to use the IP DSCP bits to
> generate
> MPLS EXP bits.
> 
> Consider a core LSR (acting as transit for LSP), why
> does it need to know about the PSCs (i.e. mapping
> EXP<=>PSC) ? 
> 
> It could possibly make all the decisions about
> internal scheduling etc based on EXP bits on the
> incoming MPLS packets.
> 
> Could someone please clarify this.
> 
> Thanks a lot for your time,
> 
> Regards,
> Vishal.
> 
> 
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