The MPLS WG Archive

[Curtis Villamizar <curtis@fictitious.org>]

In message <20030402123411.B19376@mindspring.com>, "James R. Leu" writes:
> I've been quietly following this thread, but I would like to add my $.02(US).
> 
> One of the proposed solutions to this problem is to add a 4 bit nibble after
> the label stack.  What if we trimmed it to 3 bits and threw it in the bottom
> most labels EXP bits?  A side effect of this is that networks that utilized
> hierarchical E-LSPs would be forced to convert the inner LSPs to L-LSPs.
> Although I thought at one point EXP bits were being "promoted" to the outer
> most label, but I'd have to go back add read the diffserv draft to verify.
> If this were still the case then this would free up the EXP bits for all
> labels below the top of the stack (thus alleviating the necessity to convert
> inner E-LSPs to L-LSPs).  Even if EXP bits are not being "promoted" forcing
> networks to switch to L-LSPs I think is a minimal cost to gain a finer
> granularity of ECMP.
> 
> Some might consider it a hack some might consider it an optimization, I
> like to think of it as a compromise ;-)
> 
> Jim


Its too late to completely depricate the use of EXP as COS.

Unsignaled E-LSPs seems to be the most widespread.  ECMP is being used
on them.  draft-martinni encaps is being used with control word to
make it all work where any form of PW is used.

Its not possible to make incompatible changes to the deployed base.

Even the relatively simple action of putting something reasonable in
the L3PID may meet resistance.

Curtis