Liberal label retention vs. Conservative label retention

["Tao Li" <tli@photon.poly.edu>]

Dear All,

I get confused about the label retention mode used in GMPLS. It reads
'Liberal label retention is normally used, but conservative label 
retention mode could also be used' in <GMPLS-architecture-02, Page8>.
Since GMPLS mandates downstream-on-demand label allocation with ingress
initiated ordered control, how could liberal label retention being
typically used? RFC3036 describes liberal label retention as 'When 
operating in Downstream on Demand mode with liberal label retention, 
an LSR might choose to request label mappings for all known prefixes 
from all peer LSRs.' For SONET or WDM-switch based LSRs, the above
situation will never happen.
I am a student and just begin to learn GMPLS. Your help is highly
appreciated.

Regards,

Tao Li
ECE Department
Polytechnic University
Brooklyn, NY 11201