Explicit Label Control -RSVP-TE ?

[S Ramesh <rashanmu@npd.hcltech.com>]

Hi,

In ERO the U- bit definition is not clear in 
draft-ietf-mpls-generalized-rsvp-te-04.txt.
Can anybody explain the U-bit set and unset (0 & 1).

Specifically my understanding is that if U-bit is 0 then the label is 
considered as incoming label and the outgoing label must be allocated on 
the outgoing interface and copied into upstream label object and sent 
with the outgoing PATH message.

I cannot understand when U-bit is one. Kindly explain in depth.

TIA,
Ramesh