Subject: [Mpls-interop] definition of CC and CV

From: Huub van Helvoort <[email-masked]>
Date: Wed, 18 Mar 2009 13:08:51 +0100

Hello,

During the CC last night we stopped at the point where the
CC and CV were described in the draft mpls-tp-oam-requirements
section 2.2.2.

I found that continuity and connectivity verification are
defined (for MPLS OAM) in Y.1711 where CC has the name FFD.

The CV (connectivity verification) probe is used to instrument
the availablility model of the LSP.

The CC (FFD fast failure detection) probe is used for
applications such as protection switching which require
a much faster response.

Cheers, Huub.

-- 
================================================================
                   http://www.van-helvoort.eu/
================================================================
Always remember that you are unique...just like everyone else...

---

From: Thomas Nadeau <[email-masked]>
Date: Wed, 18 Mar 2009 08:11:30 -0400

> the availablility model of the LSP.

	Yes, CVs are typically done "ad hoc" and infrequently.

> applications such as protection switching which require

	I personally don't like the term "fast" in here because it implies
that this has to run at short intervals, which in order to scale in some
situations, it cannot (and is not).  In general however, I just see  
this as
just a (more) periodic version of the CV.

	--Tom

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From: Huub van Helvoort <[email-masked]>
Date: Wed, 18 Mar 2009 13:29:52 +0100

Hi Tom,

>     Yes, CVs are typically done "ad hoc" and infrequently.

Indeed, CV is on demand probe. Probably used right after path
establishment and then every few seconds.

>     I personally don't like the term "fast" in here because
 > it implies that this has to run at short intervals,
 > which in order to scale in some situations, it cannot (and is not).

That is the reason why we use the term "CC" (and did not copy
FFD from Y.1711).

> In general however, I just see this as just a (more) periodic
 > version of the CV.

That could be a solution.
Note that CC is a proactive probe (if it is used for protection
switching).

Cheers, Huub.

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From: "LEVRAU, LIEVEN (LIEVEN)" <[email-masked]>
Date: Wed, 18 Mar 2009 13:33:52 +0100

Hi Huub and could both be used for protection switching?
Is there a difference in the packet format compared CC and CV?
Or is it a single packet type/format and the usage of the outcome that determines the CV, and CC functionality?
Thnx

./
Lieven

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of Huub van Helvoort
Sent: 18 March 2009 13:30
To: MEAD team
Subject: Re: [Mpls-interop] definition of CC and CV

Hi Tom,

Cheers, Huub.

---

From: Huub van Helvoort <[email-masked]>
Date: Wed, 18 Mar 2009 13:49:27 +0100

Hallo Lieven,

> Hi Huub and could both be used for protection switching?

That could be a possible solution.

Remember that this is text for the requirements draft.

CC nd CV are two different probes.
CC use is proactive CV use is on demand.

> Is there a difference in the packet format compared CC and CV?

Not necessarily, but again that could be a solution.

> Or is it a single packet type/format and the usage of the outcome
 > that determines the CV, and CC functionality?

That is very well possible.
The CC mechanism could just check the arrival on time of the
CC PDU, while the CV mechanism looks at the content of the CV
to take appropriate conclusions.

Cheers, Huub.

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From: Ben Niven-Jenkins <[email-masked]>
Date: Wed, 18 Mar 2009 14:22:42 +0000

Huub et al,

> establishment and then every few seconds.

I don't see how you can instrument an availability model using an on demand
probe. I interpret "instrument an availability model" to mean "be able to
record what percentage of time an LSP was in the available state"
 
I have never understood the difference between CV & CC.

To my mind:
- they both check for connectivity between connection end points
- connectivity check can be pro-active or on-demand
- if connectivity check is to be used for protection switching then needs to
run at an appropriate rate for the protection switching defined.

So it's the same function the difference is who instantiates the "check"
(OAM/router for proactive & operator/manual for on-demand) and what the rate
of packets is which is likely to be prot switching at one end (fast) then
proactive (medium) then on demand (slow).

Ben

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From: "Thomas D. Nadeau" <[email-masked]>
Date: Wed, 18 Mar 2009 10:27:42 -0400

> proactive (medium) then on demand (slow).

    Precisely the point I was trying to make. The only salient difference
seems to me at least, to be the periodicity of the operation. One is
anywhere from 0 to "ad hoc" and the other is 0 to N, where N is a
pre-defined/automated time interval.   What happens after the probe is
launched is identical.

    --Tom

-- 
Principal Architect - 21CN Networks

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From: George Swallow <[email-masked]>
Date: Wed, 18 Mar 2009 10:42:58 -0400

For MPLS OAM I've always viewed CC and CV as two different functions, where
BFD is a CC function and MPLS Ping is a CV function.  The difference being
that the former (once initialized) is a dataplane function and the latter
goes up to the control plane where you validate that the control plane and
dataplane are in sync.

Remove the control plane and the difference seems to vanish.

...George

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From: "Malcolm Betts" <[email-masked]>
Date: Wed, 18 Mar 2009 15:18:29 -0400

All, my understanding is that in the requirements should distinguish
between CC and CV.  Simplistically CC confirms that a source is "alive",
CV confirms that the "correct" source is sending the frames.  The
consequent actions for CC and CV "faults" is different (e.g. loss of CC
triggers recovery, wrong CV kills the traffic).

If the implementation chooses to use the same pdu format to support both
function then no problem but we still have two functions.

Is this correct or am I confused....

Malcolm Betts
Nortel Networks
Phone: +1 613 763 7860 (ESN 393)
email: [email-masked]

-----Original Message-----
From: [email-masked]
[mailto:[email-masked]] On Behalf Of George Swallow
Sent: Wednesday, March 18, 2009 10:43 AM
To: Thomas Nadeau; Benjamin Niven-jenkins; [email-masked]; MEAD
team
Subject: Re: [Mpls-interop] definition of CC and CV

For MPLS OAM I've always viewed CC and CV as two different functions,
where BFD is a CC function and MPLS Ping is a CV function.  The
difference being that the former (once initialized) is a dataplane
function and the latter goes up to the control plane where you validate
that the control plane and dataplane are in sync.

...George

On 3/18/09 10:27 AM, "Thomas Nadeau" <[email-masked]> wrote:

>>>>> The CV (connectivity verification) probe is used to instrument the

>>>>> availablility model of the LSP.
>>>> 
>> I don't see how you can instrument an availability model using an on 
>> demand probe. I interpret "instrument an availability model" to mean 
>> "be able to record what percentage of time an LSP was in the
available state"
>> - if connectivity check is to be used for protection switching then 
>> needs to run at an appropriate rate for the protection switching
defined.
>> (OAM/router for proactive & operator/manual for on-demand) and what 
>> the rate of packets is which is likely to be prot switching at one 
>> end (fast) then proactive (medium) then on demand (slow).
> 
>     Precisely the point I was trying to make. The only salient 
> difference seems to me at least, to be the periodicity of the 
> operation. One is anywhere from 0 to "ad hoc" and the other is 0 to N,
where N is a

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From: "Lam, Hing-Kam \(Kam\)" <[email-masked]>
Date: Wed, 18 Mar 2009 14:22:36 -0500

Malcolm,

Agree. That is my understanding too.

--Kam

> From: [email-masked]
[mailto:[email-masked]]
> On Behalf Of Malcolm Betts
> Sent: Wednesday, March 18, 2009 3:18 PM
> To: George Swallow; Thomas Nadeau; Benjamin Niven-jenkins;
> [email-masked]; MEAD team
the

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From: Huub van Helvoort <[email-masked]>
Date: Wed, 18 Mar 2009 20:40:54 +0100

Hello Malcolm and Kam,

I agree, that is what I tried to write.

Cheers, Huub.

==========================

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From: Ben Niven-Jenkins <[email-masked]>
Date: Wed, 18 Mar 2009 20:22:59 +0000

Malcolm,

Got it, thanks.

Italo/I need to ensure the OAM framework correctly articulates these
concepts as currently it treats CC/CV as one IIRC.

Ben

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From: George Swallow <[email-masked]>
Date: Wed, 18 Mar 2009 17:08:20 -0400

> Is this correct or am I confused....

This is my understanding as well.

,,,George

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From: Sami Boutros <[email-masked]>
Date: Wed, 18 Mar 2009 14:17:05 -0700

>Is this correct or am I confused....

This is my understanding too.

The implementation could choose to be different for the two functions.

Thanks,

Sami