The MPLS WG Archive

["Parmar, Pankaj N" <pankaj.n.parmar@intel.com>]

I have a doubt regarding preemption, as explained in the draft, specifically
the following statement:

"if the requested bandwidth is less than the used bandwidth then the
processing is complete. If the requested bandwidth is available, but is in
use by lower priority sessions, then lower priority sessions (beginning with
lower priority) MAY be pre-empted to free the necessary bandwidth."

It is not clear when the session gets preempted. It seems preemption could
to be done during PATH message processing, but then there is a issue here.
If a lower priority session gets preempted at a given LSR, and gets
forwarded downstream, it is possible that another downstream LSR may reject
the PATH message and send a PATH_ERR upstream. The issue is, a lower
priority session got preempted for no reason. On the other hand, if
preemption is done during a RESV message, we are more certain that we really
want to preempt a lower priority session.

Experts, please comment.

Thanks,

-Pankaj