Subject: [ippm] question

From: [email-masked]
Date: Fri, 7 Mar 2003 16:37:27 +0100

hi, i'm writing from italy, my name is david

i saw you wrote:
*******************************************************
> By the way, I have a question ... 
> What's the difference between a bottleneck b/w and an available b/w? 
> Which of b/w's can "pathchar" give me? 

The available bandwidth along a path between two Internet hosts is 
equal to the bandwidth at the bottleneck. In other words, in the 
context of pathchar, they're the same thing. 
********************************************************

yes, but pathchar doen't work with crosstraffic. the vps(variable packet
size) works
with a empty link, don't it?

the available bandwith that you mean, is the link capacity?
or if is not, what is it?

do you know any software under linux, to measure the available bandiwith
on a link? not the capacity, in the sence that this tool
should be to measure the bandwith also with crosstraffic (bing, pathchar
don't work well with traffic)

thanks,

david greco

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From: Manish Jain <[email-masked]>
Date: Sun, 16 Mar 2003 20:52:15 -0500 (EST)

Hello,

On Fri, 7 Mar 2003 [email-masked] wrote:

> > What's the difference between a bottleneck b/w and an available b/w ?

Bottleneck b/w is a very loosly defined term and has
been used at times to refer to capacity or available bw of the path.

Capacity of an end to end path is the maximum possible throughput 
when there is __NO__ cross traffic on the path. In other words, 
end-to-end capacity is equal to the minimum of hop capacities constituting 
the path.

On the other hand, available b/w of a link is unutilized capacity of the
link. So, available b/w of an end-to-end path is equal to is equal to
minimum of available bw of all links on the path.

The thing to note here is that available bandwidth and capacity
of path are equal when there is no cross traffic on the path
and available bw less than capacity in presensce of cross traffic.

> size) works with a empty link, don't it?

pathchar claims to measure per hop capcity on a end to end path.  "The
effect of layer-2 store-and-forward devices on per-hop capacity
estimation" shows that methodology used by pathchar (vps tools in general)
produces consistently erroneous results in the presence of layer-2 devices
in the measured path.

> don't work well with traffic)

pathload measures available bandwidth. "End-to-end available bandwidth:
measurement methodology, dynamics, and relation with TCP throughput"
describes the methodology implemented in the tool.

--
Manish Jain 
www.cc.gatech.edu/~jain