Subject: Re: [Mpls-interop] Connectivity Verification and Cotinuity Check in MPLS-TP

From: "Sprecher, Nurit (NSN - IL/Hod HaSharon)" <[email-masked]>
Date: Sun, 31 Aug 2008 14:42:29 +0200

Hi,

I think that most of agree that there is no real distinction between CC
and CV and that we can combine both as CC & CV function. Note that in
G.8113 they are combined. 

In order to do it (and in any case for the CV function) we need to have
a global identifier that identifies uniquely the monitored path.

BFD could be use for the CC function. The BFD session identification (My
Discriminator / Your Discriminator) has a local scope by the two ends
activating the session: the same discriminator values may be used for a
different path to be monitored by a different couple of nodes in the
same network.  When there are other means to identify the path uniquely
there is no need for the BFD session identifiers. For example with
VCCV-BFD the Discriminator fields are not used because the PW label is
sufficient to identify the BFD session. I think this is not the case for
LSP or TC. As the LSP label can be used from the interface space (i.e.
local to the interface) and in order to use it we need to understand
that the scope of the label is the interface and then use the interface
ID and the label ID as the identifier.....Since we want to have a
similar operation for section, PW/TC-PW, and LSP/TC-LSP and since that
for the CV we need to rely on identifiers uniquely assigned to a path,
we need to define a mechanism to have a unique identifier for the BFD
session.

We could for example change the semantic of the BFD discriminators to
have global scope, but we need to evaluate the case of interoperability
with MPLS BFD, etc. 

We could also think of extending BFD and define an optional global
identifiers field.

And of course we can define a new tool for the CC & CV function.

Please advice which tools should be used for the combined CC&CV function
and if it is BFD how can we have the global identifiers.

Best regards,

Nurit

________________________________

From: Weingarten, Yaacov (NSN - IL/Hod HaSharon) 
Sent: Monday, August 11, 2008 11:59
To: [email-masked]
Cc: Sprecher, Nurit (NSN - IL/Hod HaSharon)
Subject: Connectivity Verification and Cotinuity Check in MPLS-TP

Hi all,

In discussions between the authors of the OAM Analysis and OAM Framework
documents, the question was raised on the inherent differences between
the CC and CV operations and whether they are both relevant for
differentiation between on-demand and pro-active activation.  The basic
difference between the two operations is:

*         CC - checks the "continuity" of the path between two MEPs of
an ME, there are tools available that perform CC (e.g. BFD) using local
identifiers for the ME check and therefore may be subject for
border-cases of inconsistency.

*         CV - checks "connectivity" between the two ends of the ME
usually based on global identifiers, and may also give path information,
to verify that all MIPs are reacting correctly.

It is unclear whether there is a need for "On-demand CC" and "Pro-active
CV" (and there are differences of opinion) or whether the two operations
complement each other in this characteristic.  We would like to receive
some feedback from the Service Providers on whether there is a need to
separate these two operations or whether it wouldn't be best to just
talk of - "pro-active CC &CV" as opposed to "on-demand CC & CV", i.e.
combining the functionality under one roof and just differentiating
between the pro-active (or continual) CC & CV operation, and the
on-demand (in reaction to a pro-active fault, or during network periodic
checks) CC & CV?

Your comments and clarifications would be very much appreciated,

Best Regards,

Yaacov Weingarten

Nokia Siemens Networks GmbH & Co. KG

Industry Environment - CET

3 Hangar St Neve Ne'eman B

45241 Hod Hasharon, Israel

email:  [email-masked] <mailto:[email-masked]> 

 tel:     +972-9-775 1827

mob:   +972-54-220 0977

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