Subject: [Diffserv-interest] Re: MRED algorithms under DiffServ - s parameter computation

From: JORGE MANRIQUE MARGALEJO <[email-masked]>
Date: Mon, 24 Sep 2001 15:37:20

Hi Sergio,

I have not deeply studied the code you're talking about. However, as you explain in your mail, it seems reasonable to use 2 Mbps instead of 10 Mbps. Even if the "typical transmission time for a small packet" is strictly size/10Mbps, if you're limiting the bandwith to 2 Mbps you're somehow increasing the actual trasnmision time for that traffic and slowing down the "virtual link" for that traffic.

Using 2 Mbps sounds more logical to me but, as I say, I have not deeply studied the code so this is just my opinion.

Regards,

Jorge.

-------------------------

Hi! 
MRED algorithms are based on RED. In this, to compute average queue lenght 
when a packet enters an empty queue, the s parameter have to be computed (s 
in the Floyd paper, 1/PTC in ns implementation - DiffServ module). 
m is "the number of packets that might have been transmitted by the gateway 
during the time that the line was free" and s is "a typical transmission 
time for a small packet". 
My question is: 
e.g. 
I have an outgoing link of 10 Mbit/s in a DiffServ enabled router. An AF PHB 
is configured to have 2 Mbit/s of bandwidth and a MRED mechanism is applied 
to it. 
How should I compute s? Should I consider 10 Mbit/s or 2 Mbit/s? (I guess 2 
Mbit/s, but in ns 10 Mbit/s is considered). 
Thanks 
Sergio 

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From: "Sergio Andreozzi" <[email-masked]>
Date: Tue, 25 Sep 2001 11:24:49 +0300

> if you're limiting the
> bandwith to 2 Mbps you're somehow increasing the actual
> trasnmision time for that traffic and slowing down the "virtual
> link" for that traffic.

yes, you are right; but the parameter m is supposed to represent the number
of packets that might have been transmitted during the idle time for the
specific queue. Hence, the queue service rate should be used.

If you have time check http://www.aciri.org/floyd/papers/early.pdf page
20-21 and dsredq.cc file (diffserv module, ns), function setPTC and enque.

Bye

Sergio