From:
Briscoe,RJ,Bob,XVR9 BRISCORJ R
Sent: 19 August 2009
13:51
To: Moncaster,T,Toby,DER3 R;
Ruediger.Geib at telekom.de
Cc: pcn at ietf.org
Subject: RE: [PCN]
AD review: draft-ietf-pcn-baseline-encoding-04
Toby,
At 09:39 19/08/2009, toby.moncaster at bt.com
wrote:
That ASCII art is still unreadable because (for me at least)
it is getting displayed in a variable-width font (Times New Roman to be exact).
I ended up having to convert it to Courier to be able to see what you
meant…
The Tao of email says that's your problem. I sent it as
plain text (and even if I didn't it would have been Courier New (fixed)).
I am in the process of drafting a reply setting out the
background to this confusion and hopefully solving it. In the meantime there
seems to be a consensus that the way ahead is to recommend PCN as suitable for 1
or more EXISTING DSCPs (which means we need to decide which ones…). But that
still leaves the question of whether we need to say something about what needs
to happen in the future if someone (say Fred Baker) wants to add PCN to a new
DSCP.
Ruediger has suggested some. Can you check them off
against those that Fred discusses in voice-admit. That should give a decent
list.
Bob
Toby
From: Briscoe,RJ,Bob,XVR9
BRISCORJ R
Sent: 19 August 2009 09:29
To:
Ruediger.Geib at telekom.de; Moncaster,T,Toby,DER3 R
Cc:
pcn at ietf.org
Subject: RE: [PCN] AD review:
draft-ietf-pcn-baseline-encoding-04
Ruediger,
Great.
[As
some people couldn't read it, I've also replaced the diag quoted in the thread
below with narrower ASCII-art to better survive word
wrap]
Cheers
Bob
At 07:27 19/08/2009,
Ruediger.Geib at telekom.de wrote:
Hi Bob,
I agree to your
suggestion to "scrub (ii) and only have (i)..[and that] we should list classes
that might be appropriate to associate with PCN
marking."
Regards,
Ruediger
From: Bob Briscoe [ mailto:rbriscoe at jungle.bt.co.uk]
Sent: Tuesday, August 18, 2009 7:37 PM
To: Geib, Rüdiger;
toby.moncaster at bt.com
Cc: pcn at ietf.org
Subject: Re: [PCN] AD
review: draft-ietf-pcn-baseline-encoding-04
Ruediger,
The draft as
it stands holds two inconsistent opinions:
i) "
the aim is for PCN to re-use existing DSCPs
" (S.4.3.1)
ii) the
second half of Appx A.1, repeated below.
Similarly, your posting, talks
about:
i) applying PCN to existing DSCPs
ii) reserving DSCPs for
PCN.
I believe we should scrub (ii) and only have (i). In place of ii) we
should list the classes that might be appropriate to associate with PCN
marking.
In other words, we should only say that an operator _applies_
PCN marking to certain existing DSCPs.
No-one needs any additional DSCPs
to enable PCN marking. Otherwise that would waste DSCPs just to get a different
marking behaviour for packets requiring the same scheduling behaviour as a
pre-existing DSCP. The non-wasteful way to do this is to use one DSCP for a
certain scheduling behaviour, but set the ECN field to a non-zero value to turn
on PCN marking (S.4.3.1).
[In MPLS, as there is no ECN field, the
efficient way is different. Then RFC5129 describes how you would do
it.]
To be absolutely sure it's clear what I mean, here's an
example:
hi stat mux
subnet
___________________
|
same
|
| marking
|
| _____ ____:___
|
| | ||
||
--DSCPA--Not-ECT------DSCPA--NM----------DSCPA--Not-ECT--
| | ||
||
--DSCPB--Not-ECT------DSCPB--NM----------DSCPB--Not-ECT--
| |
||________||
| |
|
|--DSCPC--Not-ECT------DSCPC--Not-PCN-----DSCPC--Not-ECT--
| |_____|
|
| _____
|
| |
|
|
--DSCPD--ECT----------DSCPD--ECT---------DSCPD--ECT------
| |
|
|
--DSCPE--Not-ECT------DSCPE--Not-PCN-----DSCPE--Not-ECT--
| |_____|
|
|
:
|
|
same
|
| scheduling
|
|
(BA)
|
|___________________|
- The text on each flow shows the DSCP-ECN
combination used for that segment
- The boxes around DSCPA/B/C and around
DSCPD/E represent the same scheduling behaviour applied to multiple DSCPs in the
aggregated region (a behaviour aggregate).
- The box around NM for the first
two flows represents the same marking behaviour (PCN) applied to multiple
DSCPs.
- The flows keep the same DSCP* along their whole path, so when they
pop out into the lo-stat-mux region on the other side, the DSCP is
preserved.
- In practice, traffic might be tunnelled across the hi-stat mux
region, and at the same time common scheduling behaviours might be mapped to a
single DSCP in the outer headers. The diagram merely shows everything can be
done without tunnelling or layering.
* Note: For some non-standardised
DSCPs, the DSCP might not actually stay the same along the whole path. It might
be mapped to local DSCPs that are each used for the same class at different
points along the path.
Here's a copy of the 2nd half of Appx A.1, that I think needs to
be
removed (sorry, I know I'm a co-author, but...):
" The choice of which DSCP is most suitable
for
a given PCN-domain is dependant on the nature of
the
traffic
entering
that domain and the link rates of all the links making
up
that
domain. In PCN-domains with uniformly high
link
rates,
the
appropriate DSCPs would currently be those for the
Real
Time
Traffic
Class
[RFC5127]. If
the
PCN domain includes lower speed links it
would also be appropriate to use the DSCPs of the
other
traffic
classes that
[
Voice-Admit] defines for use with admission control,
such as the three video classes CS4, CS3 and AF4 and
the
Admitted
Telephony Class. The PCN working group will
maintain
a
list of PCN-
compatible Diffserv Codepoints.
"
At 08:55 18/08/2009,
Ruediger.Geib at telekom.de wrote:
Toby,
PCN should express to the IANA,
whether one or more new DSCP is
required to operate or carry out experiments
on PCN.
As soon as IANA maintains a list of DSCPs for any purpose, this
will have the status of a standard.
"Using pool 2 or 3 DSCPs" to me
sounds like reserving 4 DSCPs
per traffic class (DSCP bit 0-2, let's call
them traffic class
in this email) for PCN, that's 32 DSCPs in all.
If
possible, PCN should limit the number of traffic classes,
where to apply
PCN.
I don't think PCN will be applied in traffic classes 0 and
6.
I'd expect PCN to be used within traffic classes 5 and 4,
may be
also 3 or 2.
Traffic classes 1 and 7 may be excluded too.
The above
clearly expresses personal views, but informational
RFC5127 to some extent
backs these personal views.
I'm aware that PCN WG shouldn't standardise
traffic class usage
or come close to that. I however want to avoid repeating
the biggest
flaw of the AF specification, which in my eyes is to reserve
12 DSCPs for 4 traffic
classes.
Regards,
Ruediger
-----Original
Message-----
From: pcn-bounces at ietf.org [ mailto:pcn-bounces at ietf.org] On Behalf Of
toby.moncaster at bt.com
Sent: Friday, August 14, 2009 3:06 PM
To:
lars.eggert at nokia.com; pcn at ietf.org
Subject: Re: [PCN] AD review:
draft-ietf-pcn-baseline-encoding-04
Hi Lars,
Sorry not to get back
to you earlier - been busy at work so this went on
a back-burner for a few
days.
The original intention of having registration was to avoid
confusion
during any early experimental adoption of PCN however that could be
done
purely unofficially by having a list of DSCPs on the IETF wiki and
just
politely asking developers to consult it and add any new ones they
are
using. But there will need in future to be a process to
formally
register certain standards (pool 1) DSCPs as PCN-compatible since
this
effectively replaces ECN as the default behaviour for such DSCPs.
So my
suggestion is:
Change the IANA section to say something along
the following lines (I
will get IANA assistance with crafting exact
text):
"IANA will be asked to set up a registry of PCN-compatible
Diffserv
codepoints. The decision as to whether to enable PCN for a given
pool 1
codepoint must be made by the appropriate IETF Transport Area
Working
Group (TSVWG?) which will then request IANA to add this to
the
registry."
Clarify at start of A.1 that the decision of which
DSCPs to apply PCN to
has to be made by TSVWG and is separate to this
document which just
defines the process and the encoding.
Change the
last sentence of A.1 to "IANA will maintain a list of
PCN-compatible Diffserv
Codepoints."
Would this cover things appropriately? I did wonder about
asking IANA to
maintain the experimental registry but I am not sure if they
are able to
do that sort of thing? If so the following could be added to the
IANA
section:
"During the early stages of adoption it is envisaged
that PCN will be
used experimentally using pool 2 or 3 DSCPs (experimental or
local use).
Whilst these DSCPs are not controlled by IANA normally, a request
will
be made to maintain a list of PCN experiments along with the DSCPs
these
experiments are using."
Once I get the nod from WG I will
release a new version of the I-D with
these
updates...
Toby
> -----Original Message-----
> From:
pcn-bounces at ietf.org [ mailto:pcn-bounces at ietf.org] On Behalf
Of
> Lars Eggert
> Sent: 14 August 2009 12:27
> To:
pcn at ietf.org
> Subject: Re: [PCN] AD review:
draft-ietf-pcn-baseline-encoding-04
>
> Hi,
>
> I'm
waiting to hear from the authors/WG.
>
> Lars
>
> On
2009-8-5, at 17:19, Eggert Lars (Nokia-NRC/Espoo) wrote:
>
> >
Hi,
> >
> > this document is ready, except for one
issue:
> >
> > Section 7., paragraph 1:
>
>> This document makes no direct request to IANA.
However this
> > document
> >> allows for a set
of Diffserv Codepoints to be assigned different
> > ECN
>
>> semantics within a controlled domain as described in
[RFC4774].
A
> >> list of such DSCPs will be
maintained by the PCN working group.
> >
> >
DISCUSS: This text isn't aligned with appendix A.1. The text here
> >
says
> > "the WG will maintain a list of DSCPs that are
OK", while the
> > beginning of appendix A.1 says "the WG
decided to not define with
> > which DSCPs PCN can be used"
(but then the end of A.1 talks about
> > maintaining a list
again.) Which is it? If there is to be a list,
> > you
>
> need to create an IANA registry, write management procedures
for
it
> > (see RFC5226) and populate it with some
initial values. (WGs are
> > ephemeral, which is why the
PCN WG can't be the maintainer of this
> > list, IANA has
to be.) If you want to leave it fully open for
> >
deployments, you need to remove this confusion from the text.
>
>
> > Lars
> >
> >
> > Nits:
>
>
> > Section 4., paragraph 3:
>
>>
to prevent future compatability issues.
> >
> >
Nit: s/compatability/compatibility/
> >
> >
> >
Section 4.2., paragraph 1:
> >> that is guaranteeed to
be copied down into the inner header upon
> >
> >
Nit: s/guaranteeed/guaranteed/
> >
> >
> > Section
6., paragraph 1:
> >> always copy the CE codepoint from
teh outer header into the inner
> >
> > Nit:
s/teh/the/
> >
> >
> > Section 6., paragraph
2:
> >> header in decapsulation (unless the inner packet
is not-ECT).
> > If an
> >> operator it is
essential that any operator wishing to allow ECN
to
>
>> exist end-to-end ensures there are no tunnel end-points
within
the
> >> PCN-domain.
> >
>
> "If an operator it is essential that any operator..." -
wording
> >
> >
> > Section 12., paragraph 0:
>
>> 12. References
> >
> > Should be
updated; see idnits report.
> >
> >
> > Appendix A.,
paragraph 2:
> >> a given PCN-domain is dependant on the
nature of the traffic
> > entering
> >
>
> Nit: s/dependant/dependent/
> >
> >
<smime.p7s><ATT00001.txt>
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