The MPLS WG Archive

[Eric Gray <EGray@zaffire.com>]

Shahram,

	Thanks for the clarification on use of DE/CLP.

	Could you please move the paragraph that says
"the Uniform Model allows LSPs to span Diff-Serv domain 
boundaries" (toward the bottom of page 12) to a spot
closer to the point at which this model is defined (e.g.
- 2.6.3).  This paragraph makes some things much clearer. 

	Let me see if I understand now.

The reason why the penultimate hop needs to perform the
EXP'->EXP conversion is because the next hop LSR cannot
tell the difference between PHP'd packets and non-PHP'd
packets therefore all packets have to arrive with correct
EXP (or DSCP) value for the applicable LSP stacking level.

	Is this correct?

	I seem to recall that there is not a lot of current 
interest in LSPs that span service boundaries.  So is it 
fair to say that there may not be a need to support the 
Uniform model in the very near future?  Yet the Uniform
model is specified as the 'base mandatory mode'.  The Pipe
model is clearly simpler to support with or without PHP
and the biggest operational difference is that it requires
LSP tunnels to be bound by DS Domains - which is likely to
be the dominant mode of operation in any case.  Can you 
provide additional clarification on this?

	A big part of my concern is that any LSR is likely 
to need to support PHP. The Uniform model imposes additional 
configuration requirements on penultimate hops.  This is 
bound to increase the configuration required in the network 
as a whole.  While configuration is an easy out in specifying 
protocol, it's not usually a GOOD THING.  What's more, the
specification should say what approach must be provided - so
that, for example, the need to specify a standard MIB for
configuring the required information is clear.

--
Eric Gray