Subject: RE: atmVxlStatTaggedOuts

From: [email-masked]
Date: Wed, 14 Feb 2001 15:35:30 -0500

Hi Faye,

Certainly it is not an issue if policing is not supported.

As far as implementations that support policing, or rather tagging by the
policing entity:  the count implies cells carry a "tagged" attribute
separate from CLP, which they don't in their natural state, and it seems
unlikely that anyone has been able to properly implement these counters
unless their internal architecture supports this (try to find a chipset
that does!).

I am not trying to hold up the MIB, which is badly needed, but I would
prefer to see this fixed before it goes to Proposed, because I really think
it is not implementable.

Fixing the problem would amount to just changing the counter to mean "cells
tagged" rather than "tagged cells transmitted", and maybe its name to
AtmVxlStatClp0Tagged.  I am not suggesting getting rid of a "tagged cell"
count,  just correcting its meaning to accommodate the location of the
policing entity.   I do  not believe  that any significant information is
lost with this proposal.

Making the counters optional is probably the worst option, because it
leaves no standard way to report the number of cells tagged by the policing
entity, which almost all implementations COULD support.

If I am correct and  the MIB goes through as-is,  the counts should fall
out if it ever goes to Draft  because no one was able to implement  them
properly.  In the meantime people likely WILL implement them, but
incorrectly, by reporting "cells tagged by the policing entity".

Regards,

Mike

|--------+----------------------->
|        |          faye@coppermo|
|        |          untain.com   |
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|        |          02/14/01     |
|        |          02:12 PM     |
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  >--------------------------------------------------------|
  |                                                        |
  |       To:     Mike Sneed/Raleigh/ECI Telecom,          |
  |       [email-masked]                   |
  |       cc:                                              |
  |       Subject:     RE: atmVxlStatTaggedOuts            |
  >--------------------------------------------------------|

Mike,

I am not sure if output tagged cells are hard to implement or not?  There
are two situations:

1. Traffic policing is not supported

Draft 16 clearly says in this case, the output tagged cells are set to
zeros.  So there is no issue here.

2. Traffic policing is supported but output tagged cells cannot be
supported.

Draft 16 doesn't address this scenario.  I can certainly add a clause to
state that this object can be set to zero if the traffic policing entity
does not support counts of tagged output cells. Or optionally make this
object OPTIONAL in the conformance section.  I think you undestand that we
cannot get rid of the object giving the time it took us to finish the ATM 2
MIB.  People might have already implemented this object.  Actually make
another statement in section 5.1.9 is probably the safest.

What do you think?

-faye

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]
Sent: Wednesday, February 14, 2001 6:37 AM
To: [email-masked]
Subject: atmVxlStatTaggedOuts

I don't see where draft-ietf-atommib-atm2-16 did anything to address the
issues with atmVclStatTaggedOuts  and atmVclStatTaggedOuts.  I am concerned
that, if I understand these counters, they are extremely difficult or
impossible to implement.

The problem is that cells are tagged by the policing entity associated with
the INPUT interface.  I am not familiar with an reason to tag cells at
OUTPUT. So why are the tagged cells being counted at the OUTPUT interface?
The output interface has no way of knowing whether a given CLP=1 cell was
received with CLP=1, or whether it was tagged by the policing entity.   If
a CLP=1 cell is dropped after passing the policing entity, there is no way
to know whether it was a tagged cell or received as CLP=1.  So counting
CLP=1 vs tagged at output seems pretty much impossible; you can only count
transmitted CLP=1 cells, not knowing whether they were tagged or originally
CLP=1.

If I am in the weeds here someone please correct me.  Otherwise I believe
we need to look at the requirement driving the inclusion of these objects,
and find a more reasonable way of meeting it.