Subject: Re: [ippm] short preso for the jitter discussion

From: "Philip F. Chimento Jr." <[email-masked]>
Date: Tue, 01 Nov 2005 08:53:57 -0500

Hi Roman:
I looked over your slides briefly. Keep in mind that the RFC 3393  
metric was written specifically to include the ITU definition (at the  
time) as a valid instantiation of the metric. I am at a bit of  a loss  
to understand how these are seen as being in opposition. If the Asian  
and Australian operators want to use a form of the ITU definition, they  
should be able to do it, and that should also be valid for RFC 3393.

Unfortunately I cannot be at Vancouver to discuss this. However, if you  
let me know exactly what the desired definition is, perhaps I can show  
you how you can instantiate this from the RFC metric. I don't have  
access to ITU documents, so if you can send me the definition I can  
work with it.

It is not clear to me that we need a work group to deal with this...

Regards,
Phil Chimento
[email-masked]
301-580-6211

On Oct 31, 2005, at 17:03, [email-masked] wrote:

> I am attaching the short preso about the problem and issues I wanted to
> discuss during the IPPM WG meeting
> In vancouver.
> Please send ideas, suggestions or have them ready for the meeting
> thx
> roman
> (See attached file: Jitter  
> DefinitionsIPPM-DEC2005_Vancouver_2.ppt)<Jitter  
> DefinitionsIPPM- 
> DEC2005_Vancouver_2.ppt>_______________________________________________
> ippm mailing list
> [email-masked]
> https://www1.ietf.org/mailman/listinfo/ippm

_______________________________________________
ippm mailing list
[email-masked] 
https://www1.ietf.org/mailman/listinfo/ippm

---

From: Al Morton <[email-masked]>
Date: Tue, 01 Nov 2005 09:50:01 -0500

Hi Phil,

After looking at Roman's slides, it seems that he would like
to achieve harmony between jitter definitions and usage, and allow
for some differences according to the intended goal of the
measurement or the circumstances (marginal clock sync, etc.).

I think we can agree that the ITU-T Y.1540 of IP Packet Delay Variation
is similar to the RFC 3393, in that both compare the OWD of a packet with the
OWD of another packet, and that the difference emerges in the
usual form of implementation. So for those who implement:

- Y.1540, the reference packet is usually the packet from the
population of interest with the *minimum delay*.

- RFC 3393, the reference packet is usually the previous packet,
although the definition of a selection function is flexible enough
to reproduce the ITU-T Y.1540 definition. This feature was included
by design; we were trying to harmonize work between ITU-T and IETF IPPM
and you succeeded from the standpoint of definitions.

So, I think the proposal here is to compare these two different
references for assessing variation (minimum OWD, previous packet),
and it will be a good start to look at the ippm-archive back in
the autumn of 2001, if memory serves. I remember that Rudiger Geib
and Mike Pierce posted some insightful messages on this topic.

regards,
Al

At 08:53 AM 11/1/2005, Philip F. Chimento Jr. wrote:
>>DefinitionsIPPM-DEC2005_Vancouver_2.ppt)

---

From: "Philip F. Chimento Jr." <[email-masked]>
Date: Tue, 01 Nov 2005 10:08:55 -0500

Hi Al:

OK, but what you are saying implies a measurement project. Again, we 
went to a lot of trouble to make sure that the ITU definition could be 
an instantiation of the RFC 3393 metric, and it is. The issue is that 
if you want to report something meaningful, you have to say exactly 
what your selection function is, and always compare apples to apples. 
RFC 3393 allows you to do that. If you want to compare the relative 
merits of one selection function over another (with regard to fitness 
for a particular purpose) then you have to make an analytical argument 
or do an empirical study, in my opinion.

In a sense, that has nothing to do with the metric definition, and 
everything to do with what your measurement goals are. If the metric 
definition doesn't allow you to do something that you need to do, and 
which is legitimate from a statistical point of view, then we need to 
amend the definition; however, I don't see any evidence of that here...

Regards,
Phil Chimento
[email-masked]
301-580-6211

---

From: Al Morton <[email-masked]>
Date: Tue, 01 Nov 2005 10:31:59 -0500

At 10:08 AM 11/1/2005, Philip F. Chimento Jr. wrote:
>...If you want to compare the relative merits of one selection function 
>over another (with regard to fitness for a particular purpose) then you 
>have to make an analytical argument or do an empirical study, in my opinion.

Agreed, and that's my take on Roman's work proposal.  Perhaps
this work could result in an Application Statement on delay variation,
but I don't see a need to modify the definition(s), either.

Al

---

From: Alan Clark <[email-masked]>
Date: Mon, 31 Oct 2005 21:22:53 -0500

Roman

Unfortunately I won't get to Vancouver until mid-day Tuesday however 
would welcome an offline discussion on jitter, and would appreciate the 
opportunity to get involved in any jitter modeling related activity 
resulting from the IPPM meeting.  You may be interested to know that the 
time series model described in our January 2003 contribution to ITU SG12 
was used as the basis for a new IP network emulation model, recently 
adopted by SG12. 

Regards

Alan Clark
Telchemy

[email-masked] wrote:

>(See attached file: Jitter DefinitionsIPPM-DEC2005_Vancouver_2.ppt)
>
>------------------------------------------------------------------------
>

---

From: Maurizio Molina <[email-masked]>
Date: Thu, 03 Nov 2005 09:57:48 +0000

> and Mike Pierce posted some insightful messages on this topic.

The IPPM archives seem to stop at 2003....
however, I remeber a paper from Demichelis-Chimento pointing out that
taking the previous packet as a reference, you can also understand the
dynamic of IPDV, i.e. how it grows and shrinks over time. This is not
easily visible taking a fixed reference as the minimum delay. I guess
that if you reset frequently enough the choice of the fixed reference,
you can also introduce a visibility of the dynamic with the Y.1540
definition. But still, besides the "formal" similarity, there is a
conceptual (and usage) difference between the two.
Maurizio

> [email-masked] https://www1.ietf.org/mailman/listinfo/ippm

---

From: "Philip F. Chimento Jr." <[email-masked]>
Date: Thu, 03 Nov 2005 07:55:26 -0500

Hi Maurizio:

I agree that the ITU definition, and the common usage of inter-packet 
delay variation are different. The point is that RFC 3393 was written 
to allow the person/organization using the metric to define the 
selection function, which in effect defines the semantic of the metric. 
If you choose two different selection functions, you have two different 
semantics and the results of using those metrics cannot be compared 
directly, unless you establish (mathematically) a relationship between 
the two.

If you want to compare metrics, you need to argue that one or another 
is better for a particular purpose. If you want to establish one 
semantic that is optimal for ALL uses, I would be very interested to 
read the results of that research.

Regards,
Phil Chimento

---

From: Henk Uijterwaal <[email-masked]>
Date: Thu, 03 Nov 2005 16:09:45 +0100

>The IPPM archives seem to stop at 2003....

Where are you looking,

http://www.ietf.org/mail-archive/web/ippp/current

has everything up to this morning.

Henk

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From: Jing Shen <[email-masked]>
Date: Mon, 7 Nov 2005 09:23:56 +0800 (CST)

> read the results of that research.

The ppt he attached seems to be focusing on that.

Jing

		
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From: Kewin Stoeckigt <[email-masked]>
Date: Mon, 21 Nov 2005 23:11:58 +1100

Hi all,
I was wondering if there was a jitter discussion in Vancouver?
Unfortunately I wasn't in Vancouver, but I would be interested in the
outcome of such a discussion.

Kewin