Subject: Re: draft-nichols-diff-svc-arch-00.txt

From: Tony Li <[email-masked]>
Date: Mon, 1 Dec 1997 18:24:16 -0800 (PST)

In thinking about this article, it occurred to me that one of the things
missing is the lack of classification for Network Control traffic.  As
we've seen operationally, the ability to deliver such traffic in a timely
and loss free way is crticially important.  It seems like a fine solution
would be to use A&P together to indicate Control traffic.

Tony

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From: "Eric S. Crawley" <[email-masked]>
Date: Tue, 02 Dec 1997 07:46:31 -0500

Tony,

While I agree that it is important that Network Control traffic be
delivered timely and loss free, I wonder if it is possible, or even
desirable to classify Network Control traffic in the same manner that you
classify Priority traffic.  If we mark all Network Control traffic as
Priority, then we either need a hard bound on the amount of the Network
Control traffic or we will screw up the delivery commitments on the other
Priority marked traffic.  

Marking all Network Control traffic as Assured would at least keep it from
being dropped during congestion but it would not be delivered sooner than
the Priority traffic.  The problem occurs when the Network Control traffic
expands and starts competing with other Assured traffic for the same queue
space.  I don't think this is as big of a problem as with Priority traffic
and would be a reasonable compromise to provide Network Control traffic
better "Assurance" of delivery.

Of course, we could sprout a new class for Network Control traffic but it
seems that keeping the number of traffic classes to a minimum is being
encouraged these days...

	Eric

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From: Tony Li <[email-masked]>
Date: Tue, 2 Dec 1997 05:41:45 -0800 (PST)

Sorry, I should have been more explicit.  Yes, I was thinking of another
class. 

Tony

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From: [email-masked] (Kathleen Nichols)
Date: Tue, 02 Dec 1997 11:05:02 -0800

I thought Eric's comments were very much to the point. The treatment of 
Network Control traffic might be better handled by domain-specific policies
than end-to-end traffic classes. How are you proposing to treat this new
class 
of traffic within the architecture?

	Kathie

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From: Paul Ferguson <[email-masked]>
Date: Tue, 02 Dec 1997 16:41:35 -0500

>of traffic within the architecture?

I agree with this, also. Selective packet discard mechanisms can be
used within an administrative domain today to provide this functionality.

- paul

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From: Tony Li <[email-masked]>
Date: Tue, 2 Dec 1997 14:15:39 -0800 (PST)

>class of traffic within the architecture?

Selective packet discard mechanisms are dependent on the ability to quickly
recognize Network Control traffic.  The current mechanism for doing this is
via the packet precedence, which this type of architecture would hopefully
replace.  Also, selective packet discard mechanisms (at least in one
implementation that I'm familiar with ;-) do nothing to protect control
traffic transiting the box.  This is an important situation that arises
with IBGP as it could lead to protocol failures in extreme congestion and
eventual congestive collapse of the domain's routing system.

I agree that the particular policy is of less interest.  It's clear that
the default policy (not shaped, prioritized) would be fairly common, but
making it domain specific is reasonable.  However, it _is_ vital that there
be a standardized interoperable mechanism for fast classification of
control traffic.  Again, this architecture would purport to replace the
existing standard classification and this is an (the?) important
functionality of the current precedence that should be carried forward.

Tony

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From: Paul Ferguson <[email-masked]>
Date: Tue, 02 Dec 1997 17:24:51 -0500

>eventual congestive collapse of the domain's routing system.

Yes, I think I agree with all of this (since it is true, it would
behoove me to do so :-).

>functionality of the current precedence that should be carried forward.

You lost me here. Are you specifically referring to the draft in the
subject line, or is this a generic statement on the effects of SPD-like
mechanisms & control traffic in general? Quite frankly, I believe that
draft-ferguson-delay-drop-00.txt makes this a no-brainer.

- paul

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From: Tony Li <[email-masked]>
Date: Tue, 2 Dec 1997 14:53:14 -0800 (PST)

Paul,

   Are you specifically referring to the draft in the subject line, 

Yes.

   Quite frankly, I believe that draft-ferguson-delay-drop-00.txt makes
   this a no-brainer. 

Agreed.  However, that's a bit encoding for the classification, not an
entire service architecture.  The Nichols draft proposes a service
architecture but omits the (IMHO) necessary fast classification of control
traffic.  

Tony