Subject: Doubt regarding Explicit NULL label usage with PHP

From: "venkattr" <[email-masked]>
Date: Tue, 18 Jun 2002 20:13:52 +0530

Hi All,

One of the popular solutions proposed to maintain QoS information from the
penultimate hop to the Egress when PHP is implemented, is to insert an
EXPLICIT NULL label with the QoS information encoded into the EXP bits.  It
is here that I have a gap in my understanding.  The determination of QoS
behaviour to be applied to any MPLS packet depends not just on the EXP bits,
but also on the combination of Label + EXP for both Signalled E-LSPs and
L-LSPs.  The only exception is in the case of Pre-Configured E-LSPs when the
EXP bits by themselves are sufficient for the complete determination of the
QoS behaviour.  In that case, is the use of EXPLICIT NULL label with the EXP
bits encoded to convey QoS information between Penultimate Hop and Egress
restricted to Pre-Configured E-LSPs?

Any valuable inputs will be highly appreciated!

Thanks and regards,

-TRV

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---

From: Shahram Davari <[email-masked]>
Date: Tue, 18 Jun 2002 09:01:09 -0700

In PHP case, the egress LSR distributes the Implicit Null label (3) to the
penultimate node, and that node just pops the top label and forwards it. 
There is no label insertion.

If we assume that the explicit null label has been inserted by ingress,
and there is another label above it, then your point is valid for the
uniform tunnel mode.

-Shahram

> -----Original Message-----
> From: venkattr [mailto:[email-masked]]
> Sent: Tuesday, June 18, 2002 10:44 AM
> To: [email-masked]
> Subject: Doubt regarding Explicit NULL label usage with PHP
> 
> 
> Hi All,
>