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Why LSR need to know of EXP<->PSC maps in MPLS DiffServ model

  • From: Vishal M <vishal_study@yahoo.com>
  • Date: Thu, 15 Nov 2001 16:00:28 -0800 (PST)
  • Cc: te-wg@ops.ietf.org


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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