The MPLS WG Archive

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

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:venkattr@future.futsoft.com]
> Sent: Tuesday, June 18, 2002 10:44 AM
> To: mpls@UU.NET
> Subject: Doubt regarding Explicit NULL label usage with PHP
> 
> 
> 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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