Subject: [Diffserv] LBE using RFC 2474

From: Brian E Carpenter <[email-masked]>
Date: Wed, 10 Nov 1999 13:00:27 -0600

Kathie and I discussed the less than best effort requirement expressed
by some people, and concluded that this can be done using RFC 2474
with no change:

In the DSCP to PHB mapping table, map the DSCP value 0 (default)
to the PHB Class Selector 2. Then classify the "LBE" tarffic
into a BA that receives PHB Class Selector 1.

This usage overrides the SHOULD in RFC 2474, section 4.2.2.2,
but that is why we use SHOULD instead of MUST.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Brian E Carpenter (IAB Chair)
Program Director, Internet Standards & Technology, IBM 
On assignment for IBM at http://www.iCAIR.org 
Attend INET 2000: http://www.isoc.org/inet2000
Non-IBM email: [email-masked]
Ethernet address: 00-00-AC-CF-5B-82

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From: Klaus Wehrle <[email-masked]>
Date: Thu, 11 Nov 1999 11:49:19 +0100

> by some people, and concluded that this can be done using RFC 2474

When you override the SHOULD  in RFC 2474, section 4.2.2.2 this would be a
change ;-)

> into a BA that receives PHB Class Selector 1.

nice trick, but if an ISP do not use this mapping, the LBE-traffic would
not be treated lower than Best-Effort.

If you use a seperate Codepoint for LBE, every router can distinguish it
from BE, independant from the mapping of LBE-traffic into a BA that
receives lower than BE.
I think, there are enough Codepoints left, so why don't we assign one to
LBE.

If you map BE to ClassSel 2, LBE to ClassSel 1, then you can map EF to the
highest ClassSelector and we can forget RFC 2598. I think, that is not was
the people on the DiffServ-WG-list want.

I don't know, if every ISP wants to offer services, that only bases on AF
or EF or the ClassSelectors.

> but that is why we use SHOULD instead of MUST.

--------------------
Ciao,
Klaus

--

 Klaus Wehrle
 Institut für Telematik, Universität Karlsruhe (TH)
 Zirkel 2, 76128 Karlsruhe, Germany
 Phone: +49 721 608 6414, Fax: +49 721 388097
 mailto:[email-masked]
 http://www.telematik.informatik.uni-karlsruhe.de/~wehrle

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From: Brian E Carpenter <[email-masked]>
Date: Thu, 11 Nov 1999 06:04:16 -0600

> When you override the SHOULD  in RFC 2474, section 4.2.2.2 this would be a

No, there is no law against overriding a SHOULD. I mean literally that
not one word in 2474 needs to be changed.
> not be treated lower than Best-Effort.

That applies to every PHB not implemented by any ISP. Nothing new here.

> from BE, independant from the mapping of LBE-traffic into a BA that

Only if operators choose to implement it. PHBs are not compulsory.

> I think, there are enough Codepoints left, so why don't we assign one to

Because we already have too many defined.

> the people on the DiffServ-WG-list want.

No, there is a very clear distinction between EF and the class
selectors,
and we spent months getting consensus on that. 

> or EF or the ClassSelectors.

Neither do I, but what I hear from ISPs is that there are already
plenty of PHBs, thankyou, and what they need to offer services
are service management mechanisms, not new PHBs.

  Brian

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From: Kathleen Nichols <[email-masked]>
Date: Thu, 11 Nov 1999 06:18:57 -0800

> > Brian E Carpenter wrote:
...
> and we spent months getting consensus on that.

Just to clarify this slightly minor point: You can certainly map
traffic which is marked for the EF PHB to the same queue as Class
Selector 7 (though I think CS 5 would be a better choice), but
then you must ensure that the behavior aggregate of that queue
is getting the treatment described in RFC2598. RFC 2598 isn't
meant to say that there must be another queue if you have 8
CS-compliant ones, it is not meant to say that you must use
the recommended DSCP for it. It just give rules for how a particular
behavior aggregate must be treated at each diffserv node in order
for it to be getting the "EF per hop forwarding treatment". The
reason RFC2598 calls out the specific details of that PHB is that
it is thought to be a useful building block that allows you to
build services whose behavior can then be characterized explicitly
assuming each node has been properly configured according to
RFC2598.

	Kathie

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From: Juha Heinanen <[email-masked]>
Date: Wed, 17 Nov 1999 02:08:05 +0200 (EET)

> not be treated lower than Best-Effort.

no isp will blindly map code points.  if my isp neighbor tells me that
in the packets that they send to me, prec 1 means background SERVICE,
then i map prec 1 at the boundary to whatever i use for background in my
network.  new phbs should not be defined just in order to standardize
code point for SERVICES.  write a background service spec instead.

-- juha

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From: Roland Bless <[email-masked]>
Date: Fri, 19 Nov 1999 10:43:25 +0100

> code point for SERVICES.  write a background service spec instead.

A service is something with "end-to-end" semantics whereas a PHB
describes a forwarding treatment applied at a differentiated
services-compliant node to a behavior aggregate. The latter applies
exactly to our LBE motivation and definition and we do not specify a
particular behavior for more than one hop. It is clear that a background
service may be constructed by using the defined LBE behavior which may
be realized by using other PHBs as a basis, but this is also true for EF
or AF with respect to class selector compliant PHBs. I suppose that most
confusion about the LBE PHB is caused by its name and everybody using
another interpretation of its supposed meaning. However, its name also
expresses its relation to the BE aggregate and that was the main
intention behind the name.

Roland

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From: Grenville Armitage <[email-masked]>
Date: Fri, 19 Nov 1999 10:58:40 -0800

Roland Bless wrote:
> particular behavior for more than one hop.

So that was Juha's point - you appear to be defining a new PHB when in
fact you are really looking for a new service. And some of the feedback
you are being given is that your desire for 2 levels of BE service
can be achieved with suitable use of existing PHBs.

> It is clear that a background
> be realized by using other PHBs as a basis,

Cool. Are we finished now?

cheers,
gja