Subject: RE: [ippm] Request for speaking slot:draft-anjali-ippm-avail-band -measurement-00.txt

From: Bennett Jon-MGIA0444 <[email-masked]>
Date: Thu, 7 Nov 2002 18:19:38 -0500

> In addition, I see a number of claims made without
> proof here (one that caught my eye: "it is accurate as
> it obtains measurement from the network using a TCP session").
> I have not followed reference [6] to see what is stated
> there.
> 
> Do other group members have comments?

what happens when multiple people perform the test at the same time? is the
available bandwidth = the available bandwidth? or = avail bw / number of
testers?

one part that I was particularly scared by was

>It has to be noted that our scheme will have difficulty in
>   measuring bandwidth for paths with high capacity links. This is
>   because of the limitations in TCP operation like buffer size,
>   segment size etc. For paths with high capacity links, our method
>   can be extended to include multiple TCP sessions to be initiated in
>   parallel. These multiple sessions can probe the network and obtain
>   fair share estimates of the path available bandwidth. These
>   sub-estimates can then be added to obtain proper estimates for the
>   path.

this strikes me as standardizing a DDOS mechanism :)

jon
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---

From: "Patrik Carlsson" <[email-masked]>
Date: Fri, 8 Nov 2002 08:57:58 +0100

This way of measuring, couldn't it cause the "link" to fluctuate? 
TCP can be seen as greedy/friendly with regards to link capacity (LC),
some streams get good deal of the LC whereas others starve. This could
cause a link to look good from some streams whereas "bad" to others,
depending of view point. 
 
What happens when the distance between the sender and receiver is so
large, that there is more than one way to get there? For how long will
test run? Until all possible routes have been tried and estimated? Or
should the estimation be on a "virtual" point-to-point connection
between sender and receiver, since this is what the user perceives. On
the other hand, if there is only a small number of possible routes
in-between sender and receiver, preferably only one, I think it could
work. As long as there is only one test going on (on all of the links
that the stream passes).
 
Regards,
 
Patrik Carlsson
 
Blekinge Institute of Technology
Dept. Telecommunications and Signal Processing
371 79  KARLSKRONA
SWEDEN

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]] On
Behalf
> Of Bennett Jon-MGIA0444
> Sent: den 8 november 2002 00:20
> To: 'Matthew J Zekauskas'; Tricha Anjali
> Cc: Merike Kaeo; [email-masked]
> Subject: RE: [ippm] Request for speaking slot:draft-anjali-ippm-avail-
> band-measurement-00.txt
> 
> 
> 
> 
> 
> what happens when multiple people perform the test at the same time?
is
> the

---

From: Tricha Anjali <[email-masked]>
Date: Fri, 8 Nov 2002 12:24:29 -0500 (EST)

On Thu, 7 Nov 2002, Bennett Jon-MGIA0444 wrote:

> available bandwidth = the available bandwidth? or = avail bw / number
> of testers?
>

In a big network, the probability of two identical simultaneous events
decreases with size. In other words, the probability of multiple users
desiring path available bandwidth measurement simultaneously is low.
However, in the rare case that this happens, it is desirable to have a
conservative estimation of the path available bandwidth. If the users are
measuring the available bandwidth at an instant, it is foreseeable that
they will send traffic to use that measured value of bandwidth. Thus, it
is efficient to give to them a partial visibility of the total path
available bandwidth.

> this strikes me as standardizing a DDOS mechanism :)

Since there are no special features added by our method to a simple TCP
transfer, we are not adding any security concern. Sending a TCP flow is a
task that does not need any special privileges.

> jon

Regards,
Tricha

-------------------------------
Tricha Anjali
Broadband & Wireless Networking Lab
School of Electrical and Computer Engineering
Georgia Institute of Technology
http://users.ece.gatech.edu/~tricha/

---

From: Tricha Anjali <[email-masked]>
Date: Fri, 8 Nov 2002 12:45:59 -0500 (EST)

> cause a link to look good from some streams whereas "bad" to others,

This is an inherent TCP drawback. TCP issues have been extensively studied
and many versions have been proposed to handle these drawbacks in
different environments, such as TCP Peach for handling large RTT scenarios
and TCP NewReno for terrestrial networks. Depending on the path
characteristics, suitable version of TCP can be applied to our method to
provide an objective viewpoint of the path to all flows.

> work. As long as there is only one test going on (on all of the links

Our method measures the available bandwidth on the path that is the
current IP-selected path between the source and the destination. Thus, in
the scenario when there are multiple paths between the sender and the
receiver, the measurement will be obtained for the path that is obtained
by IP lookups in the successive routers in the path. Our method is
designed for IP-based application users.

Regards,
Tricha

---

From: "Henk Uijterwaal (RIPE-NCC)" <[email-masked]>
Date: Tue, 12 Nov 2002 13:45:43 +0100 (CET)

> is efficient to give to them a partial visibility of the total path

I think that you are mixing 2 things here: (1) the result when >1 user
uses this tool to estimate available bandwidth and (2) what to do with the
result.

For (1) the result should be "measured available BW = available BW - BW
used by other measurement sessions".  Since the latter should be small,
multiple users at the same time should measure the same result.  This has
to be verified, obviously.

(2) is a completely different question.  It would be very nice if the
system could somehow detect that >1 user is measureing available BW and
tell it that each user can use only 1/N-th of the result, but this is
impossible.  This requires some BW reservation mechanism, but that is
outside the scope of this WG.

> > >   measuring bandwidth for paths with high capacity links.

It would be nice if the draft could quantify this in terms of network
parameters such as link capacity, time-stamp accuracy, etc, or at least
describe how measure it for a specific link.

Henk

> > This is

> task that does not need any special privileges.

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That problem that we weren't having yesterday, is it better? (Big ISP NOC)