[mpls-tp] Comment on http://www.ietf.org/id/draft-sfv-mpls-tp-fault-01.txt

[Maarten Vissers <[e-mail]>]

Some comments on the content of this draft:

In section 2.1 it is stated: 
"  <..>
   For example an AIS message may be sent during a protection switching
   event and would cease being sent if the protection switch was
   successful in restoring the link.

   Its primary purpose is to suppress alarms in the MPLS-TP layer
   network above the level at which the defect occurs.  The AIS message
   MAY be used to trigger recovery mechanisms.  It should be noted that
   such use would be subject to false positives, e.g. unnecessary
   protection switching events in the client layer."

It is not correct to state that AIS sending is stopped if the protection
switch was succesful. The reason is that the AIS insertion is done by a MEP
Sink function that is upstream of the protection switch selector process,
and this MEP Sink function is as such unaware of the presence of a
protection switch process and of the state of the protection switch process.

AIS in packet transport networks must **not** used to trigger recovery
mechanisms. Reason is that AIS OAM messages in packet transport network are
to be generated within 1 second after the detection of the signal fail type
defect detection and be generated with a periodicity of 1 second. These
times are much too long to trigger any recovery mechanism.

The 1 second time requirement to generate the first AIS message is derived
from the 2.5 +/- 0.5 second fault cause to failure integration timer as
specified in G.7710. Generation of the first AIS message within a period of
1 second will leave enough time to reach the downstream MEP Sink function
and suppress the fault cause that report the interruption of the connection.

Protection switching in packet transport networks is triggered by e.g. loss
of continuity and misconnection defects.

In section 2.2 it is stated:
"  The LDI message is generated in response to detecting a fatal failure
   in the server layer.  The LDI message MUST NOT be sent until the
   defect has been determined to be fatal.  For example during a
   protection switching event LDI messages are not sent.  However if the
   protection switch was unsuccessful in restoring the link within the
   expected repair time, an LDI message MUST be sent."
and in section 2.1 it is stated:
"  The MPLS-TP Alarm Indication Signal (AIS) message is generated in
   response to detecting defects in the server layer.  The AIS message
   SHOULD be sent as soon is the condition is detected, that is before
   any determination has been made as to whether the condition is fatal."

This draft suggest that it is possible for a MEP Sink function to determine
if the fault is *fatal* or *not fatal*. This is not possible for a MEP Sink
function. The reason is that a MEP Sink function has no knowledge of the
presence or state of a protection switch process associated with the
connection. E.g. the protection switch process may be in a downstream node.

It is also not necessary to make AIS generation conditional on e.g.
protection switch actions. Reason is that a protection switch process will
select traffic from either a working connection input port, or a protection
connection input port. Any traffic present on the not selected input port
will drop at this input port and not be forwarded to the protection switch
process output port. At the output port AIS messages will be present as long
as the protection switch process selects its traffic from the failed
connection; once the protection switch process selects its traffic from the
non-failed connection AIS messages will not longer be forwarded to the
output port.

This draft should as such not become a WG document.

Regards,
Maarten

-----Original Message-----
From: [e-mail] [mailto:[e-mail]] On Behalf
Of Loa Andersson
Sent: donderdag 17 december 2009 5:36
To: [e-mail]; [e-mail]; [e-mail]; [e-mail]
Subject: [mpls-tp] Poll om making
http://www.ietf.org/id/draft-sfv-mpls-tp-fault-01.txt a working group
document

All,

this is to start a two week poll on making

http://www.ietf.org/id/draft-sfv-mpls-tp-fault-01.txt

an MPLS working group document.

Send a mail to the [e-mail] mailing list, indicating "yes/support"
or "no/do not support".

Comments on the content of the draft should be sent to the same mailing list
with a different subject line.

The poll ends Friday 15 Jan, 2010.

/Loa
-- 


Loa Andersson                         email: [e-mail]
Sr Strategy and Standards Manager            [e-mail]
Ericsson Inc                          phone: [phone]
                                              [phone]
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