Re: Measuring impairments [Was: Updated Draft Liaiosn to Q6/15]

[Igor Bryskin <[e-mail]>]

I agree with Enrique (if, of course, I understood him correctly). We want to advertise things that help to constrain path computation so that resulting paths will likely to be satisfactorily from the impairments point of view. I don't see much value in measurement of optical impairments on existing paths, other than improving  the quality of things we  advertise and hence future path computation results.

Igor




________________________________
From: "Hernandez-Valencia, Enrique (Enrique)" <[e-mail]>
To: Adrian Farrel <[e-mail]>; Giovanni Martinelli <[e-mail]>; Malcolm Betts <[e-mail]>; "O'Connor, Don" <[e-mail]>
Cc: [e-mail]
Sent: Tuesday, March 10, 2009 1:31:33 PM
Subject: RE: Measuring impairments [Was: Updated Draft Liaiosn to Q6/15]

Adrian,

If one replaces "optical impairments" for "packet impairments" (e.g.,
excessive BER, excessive PLR, excessive delay/delay variation) and
compares that with what CCAMP currently does for PSC technologies, would
that help clarify what CCAMP wants to do for WSON?

It would seem the focus of the CCAMP protocol extension would be on
advertising budgets/objectives not on actual impairment measurements.

Regards, 
Enrique

-----Original Message-----
From: [e-mail] [mailto:[e-mail]] On
Behalf Of Adrian Farrel
Sent: Tuesday, March 10, 2009 12:48 PM
To: Giovanni Martinelli; Malcolm Betts; O'Connor, Don
Cc: [e-mail]
Subject: Measuring impairments [Was: Updated Draft Liaiosn to Q6/15]

I'm going to try to answer all of the comments about measuring
impairments 
in one email.

I'm arguing all of this from an abstract point of view. I want to "out"
in 
advance of the meeting as much of opinion held in CCAMP. I do not
believe it 
is valuable to go into the meeting expressing what we think may be Q6's 
view. Instead, we need to say what it is people in CCAMP may want to do.

Then we can get Q6 feedback on whether that is practical and what the 
concerns are.

So...

The ability to measure optical impairments on an active path is claimed
by 
several vendors. I am not in a position to judge whether they are
successful 
or not.

Giovanni reasonably asks "what exactly you mean by *ability to
measure*?"

We are proposing protocol extensions that allow nodes to distribute 
information about optical impairments. It is not our business to define
from 
where this information is gathered. We can observe that the information 
might be configured, might be measured during network provisioning and
held 
static, might be determined by a node applying some algorithm to
configured 
on pre-measured information, or might be measured dynamically. So we can

choose between:
- optical impairments can be advertised, but cannot be updated
- optical impairments can be advertised, and can be updated

If we choose the first of these, it seems that we are shutting out what
some 
people want to be able to do. If we choose the latter, we are not
requiring 
anyone to update the information they advertise, but we are allowing
this to 
be done if a node chooses to do so.

To answer Don specifically, I see no proposal in CCAMP about which 
impairments could be measured or how they would be measured. But, to
turn 
this point around, I do not believe that CCAMP should say "you must not 
measure an impairment". As Don says, this is outside our remit.

Malcolm's suggestion doesn't cut it for me.
By saying "We understand that Q6 currently has no requirement to measure

impairments after the transport equipment is deployed" we miss the
point. 
The point is not what Q6 requires or does not require, but is what CCAMP

requires.

So I wonder what is wrong with the statement (in the context of
describing 
what CCAMP wants to do) that "There is no requirement to measure 
impairments."

Don objected specifically to...
>    However, if an implementer chooses to measure impairments
>    on their device, this should not be prohibited, and should be
>    accommodated.

How would it be if we defered the practicality of such measurements to
the 
ITU? We could then write...

    However, if an implementer chooses to measure impairments
    on their device, and this can be achieved within the mechanisms
    and definitions defined by the ITU-T, then this should not be
    prohibited by the CCAMP protocol mechanisms, and should be
    accommodated within GMPLS.

Cheers,
Adrian