Subject: [ippm] draft-ietf-ippm-multimetrics

From: Henk Uijterwaal <[email-masked]>
Date: Tue, 21 Mar 2006 16:47:03 +0100

More reading...

Section 2.2: I'm not sure if I understand this.  Aren't there always hosts
  involved that are not the source or destination of a packet?

3.1: Why is the PSAMP work related, isn't that about passive sampling
  of packets, aren't we generating our own traffic here?

3.3: I think this is the first time group-to-group comes up.  Why discuss
  it before it has been defined what it is?

Section 5: In the one-to-group metrics, isn't it easier to say:
   type-p-one-to-group-delay = is a set of type-p-one-way-delays (RFC2679),
   without rerunning the whole definition.

5.4.1. I'm sure one can calculate the mean of a one-to-group delay but
  what does that say about the network?

Henk

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1160438400. Watch this space... 

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From: Henk Uijterwaal <[email-masked]>
Date: Wed, 22 Mar 2006 17:39:28 +0100

Hi Lei,

>I wouldn't say that the type-p-one-to-group-delay = a set of
>type-p-one-way-delays. a set of type-p-one-way-delays could be a
>collection of metrics measured at different time, using different test
>packets while type-p-one-to-group-delay specifies the measurements to a
>particular set of test packet during the same sampling interval.

That's not what I meant: it looks as if a lot of parameters in the
group-delay are the same as the one-way.  So, I'd define it as
group-delay = a set of one-way delays with a number of parameters that
are common for the set and perhaps some extra. In the draft, just list
what should be common.

>Furthermore, type-p-one-to-group-delay has different metric parameters
>that make things much clear, such as how many hosts involved, who those
>hosts are, whether unicast or multicast or even broadcast. The
>definition is more general than one-way metrics.
>
> >
>The mean of one-to-group delay gives a clue of how good or bad every
>user is served.

Suppose I have one sender S and 2 recipients A and B.  A is close to
S, B is far away from S.  I first measure 1-1 delays and get (say) 10
ms for S-A and 20 for S-B.  I now measure the group and get the set
(10, 20), or a mean of 15.   It now appears that A is served a lot worse
and B a lot better than the case of the individual measurements.  But
of course, all you see is are distance effects.

More general, the mean seems to be a mix of distance and performance.
I don't think that is very useful.

Henk

>It's just like people define the end-to-end delay as the
>mean of the one-way delay over a period of time, which is over the time
>zone where the mean of one-to-group delay is over the space zone. The
>mean of one-to-group delay shows if most of the users are served with
>satisfied performance. If the mean of one-to-group delay is too high
>that means some or even most of the users are suffering from the service
>(i.e. media multicast/broadcast) you provide and investigation will be
>needed to find out what is the problem. There are many possible ways to
>solve the problem, e.g. manipulating the traffic priority, path
>re-allocation, server re-assign, etc. But it's beyond the draft.
>
>
> >
> > Henk
> >
> >
> >
> >
> >

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From: lei Liang <[email-masked]>
Date: Wed, 22 Mar 2006 17:36:35 +0000

Hi, Henk,

> are common for the set and perhaps some extra. In the draft, just list
Yes. We were trying to define the group-delay in the same way as the
definition of one-way. Maybe we can define the group-delay as a set of
one-way delays with respect to the same test packet from the src to
receivers.Is that what you mean?

> I don't think that is very useful.

Ok, firstly, the difference between performance to different users are
not only caused by distance but also network situations, e.g.
congestion, path choosing, different network barriers and etc. Secondly,
"mean" is a statistic term. Applying it to two or several users doesn't
make sense. Thirdly, as I mentioned, it should be used with another
metric, the Variation, to give a rather clear picture of the network.
It's just an example of statistic use of the defined group-metric.
Therefore, it may not be general enough but service oriented. 

Regards,
Lei

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From: lei Liang <[email-masked]>
Date: Wed, 22 Mar 2006 15:43:52 +0000

Hi, Hank, 
  Thank you very much for your comments.  Please see the response in
line.

>   it before it has been defined what it is?

Agree. We can move it down to section 5.5. 

user is served. It's just like people define the end-to-end delay as the

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From: Henk Uijterwaal <[email-masked]>
Date: Wed, 22 Mar 2006 23:58:42 +0100

Hi,

>receivers.Is that what you mean?

Yes.

>Therefore, it may not be general enough but service oriented.

I agree with all this, so where do you see a mean being used then?

Henk

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From: lei Liang <[email-masked]>
Date: Thu, 23 Mar 2006 12:42:04 +0000

Hi, Henk,

> I agree with all this, so where do you see a mean being used then?
The concept of the mean of delay has been used in many projects, such as
ETSI TIPHON project which gives the recommended classes of performance
parameters for real-time online conferencing service. The particular
group delay mean is a new definition based on this concept and a paper
has been produced using the group delay and variation as parameters for
online gaming performance optimization in IEEE Communication Magazine,
Vol. 43, No. 5, May, 2005, pp 75-83, named "Relative QoS Optimisation
for Multiparty Online Gaming in DiffServ Networks". the group statistic
will also be used in an EU project soon as well. Hope that answered your
question.

Cheers,
Lei