hi j-l
LE ROUX Jean-Louis RD-CORE-LAN wrote:
Hi Dimitri,
-----Message d'origine----- De : dimitri papadimitriou
[mailto:[EMAIL PROTECTED] Envoyé : vendredi 14 juillet 2006
15:44 À : [EMAIL PROTECTED] Objet : [Pce] P & I flags
the comments around the P and I flags are
o) we have two levels of optionality in listing the protocol object
and usage level of the protocol object - however it is much more
appropriate to be sure that mandatory constraints have been taken
rather than having the optional having been taken into account
As clearly pointed out in the same setion of the draft, if a
mandatory constraint cannot be handled the PCE replies with PCErr
message
i restate you have two levels of indirection optional objects and
optional usage of the constraint during pc
now the important thing is not that you have a "PCE deciding to ignore"
but a PCC that performs a sort on constraint it wants to see as part of
its comp request
p flag can be used when the pce can't compute with that constraint(s)
and sends a negative answer with the P flag on the constraints that can
not be taken into account
in the reply the P flag should be such that the requestor receives a
confirmation of constraints taken into account during PCE pc - since
this is the only thing PCC cares about and return an error if the object
is not supported or decision with "Policy Control failure" or even "AC
failure" in case of PCE overload
"If the PCE does not understand an object with the P Flag set or
understands the object but decides to ignore the object, the entire
PCEP message MUST be rejected and the PCE MUST send a PCErr message
with Error-Type="Unknown Object" or "Not supported Object".
my point is that you can not return "unknown object" from the P flag but
from the unsupport of an object
If the PCE can handle all mandatory constraints it replies with a
PCRep message (either positive or negative if there is no path), else
it sends a PCErr message. Hence the PCC knows whether mandatory
constraints have been taken into account.
you have also a third level of indirection in the reply because one
assumes that
P flag (Processing-Rule - 1-bit): the P flag allows a PCC to
specify in a PCReq message sent to a PCE whether the object must be
taken into account by the PCE during path computation or is just
optional. When the P flag is set, the object MUST be taken into
account by the PCE. Conversely, when the P flag is cleared, the
object is optional and the PCE is free to ignore it if not
supported.
o) on the I flag issue is identical why include an object which has
not considered during computation ?
I don't catch your point, the PCC may want to know the constraints
that were not taken into account during path computation, this sounds
quite important isn'it?
there are so
many things that the PCE has not taken into account during
computation so why bother ?
Hum I don't follow you here "there are so many things...", What do
you mean?
see adrian's reply
thanks,
- dimitri.
it is imho more important to include the mandatory object not taken
into account
If a mandatory object is not taken into account, you cannot compute
the path and you send an error message. I agree with you that this
would be useful to include within the PCErr the set of objects not
supported, this can be clarified in next revision.
I flag (Ignore - 1 bit): the I flag is used by a PCE in a PCRep
message to indicate to a PCC whether or not an optional object was
processed. The PCE MAY include the ignored optional object in its
reply and set the I flag to indicate that the optional object was
ignored during path computation. When the I flag is cleared, the
PCE indicates that the optional object was processed during the
path computation. The setting of the I flag for optional objects
is purely indicative and optional. The I flag MUST be cleared if
the P flag is set.
o) the result of all these flags is that a PCC can be wrapping
around unknown constraints create processing churn on the PCE;
OK, if you mean that we should include the unsupported object(s)
within the PCErr, then we are in sync
Thanks for the comment
Regards
JL
If the PCE does not understand an object with the P Flag set or
understands the object but decides to ignore the object, the entire
PCEP message MUST be rejected and the PCE MUST send a PCErr
message with Error-Type="Unknown Object" or "Not supported Object".
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