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Detlef Bosau wrote:
<blockquote cite="mid458DA380.1070207@web.de" type="cite">I apologize
if this is a stupid question.<br>
</blockquote>
<br>
I admit, it was a <b>very</b> stupid question :-)<br>
<br>
Because my ASCII arts were terrible, I add a nam-screenshot here
(hopefully, I´m allowed to send this mail in HTML):<br>
<br>
<img alt="NAM screenshot" src="cid:part1.00010808.06080109@web.de"
height="589" width="627"><br>
<br>
Links: <br>
0-2: 100 Mbit/s, 1 ms<br>
1-2: 10 Mbit/s, 1 ms<br>
2-3: 100 Mbit/s, 10 ms<br>
3-4: 10 MBit/s, 1 ms<br>
<br>
Sender: 0,1<br>
Receiver: 4<br>
<blockquote cite="mid458DA380.1070207@web.de" type="cite"><br>
<br>
My feeling is that the flow server 1 - client should achieve more
throughput than the other. From what I see in a simulation, the ratio
in the secnario above is roughly 2:1. (I did this simulation this
evening, so admittedly there might be errors.)
<br>
<br>
Is there a general opinion how the throughput ratio should be in a
scenario like this?</blockquote>
<br>
<br>
Obviously, my feeling is wrong. Perhaps, I should consider reality more
than my feelings <span class="moz-smiley-s6"><span> :-[ </span></span><br>
<br>
AIMD distributes the <b>path capacity (i.e. "memory") </b>in equal
shares. So, in case of two flows sharing a path, each flow is assigned
an equal window. Hence, the rates should be equal as they depend on the
window (= estimate of path capaciyt) and RTT. (Well known rule of
thumb: rate = cwnd/RTT)<br>
<br>
However, the scenario depicted above is an interesting one: Apparently,
the sender at node 1 is paced "ideally" by the link 1-2. So, packets
sent by node 0 are dropped at node 3 unuduly often. In consequence,
the flow from 0 to 4 hardly achieves any throughput whereas the flow
from 1 to 4 runs as if there was no competitor.<br>
<br>
If the bandwdith 1-2 is changed a little bit, the bevaviour returns to
the expected one.<br>
<br>
I´m still not quite sure whether this behaviour matches reality or
whether it is an NS2 artifact.<br>
<br>
Detlef<br>
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