Re: [Linux Diffserv] GRED queueing discipline and the filesch_gred.c

Re: [Linux Diffserv] GRED queueing discipline and the filesch_gred.c

[Rahul Hari]

Thanks for all the suggestions Jamal and Thomas.
>From what you people have been suggesting, i feel that i should be
giving a brief explaination of the problem I am currently working on.

I have divided all the traffic on a network into 5 categories : Real
time video (UDP1),Real time audio (UDP2), TCP not requiring any QoS
(TCP1), TCP requiring QoS but with the size of the entire transaction
very low(TCP2), and TCP requiring QoS with the size of the transaction
in several MBs (TCP3).

Now I am putting UDP1 and TCP1 in one particular queue (say q1) and
giving priority to UDP1 (for dequeuing not caring if TCP1 is getting
starved). I am putting UDP2 ,TCP2 and TCP3 in a different queue (thus
keeping the average queue length almost constant) (say q2)and applying
RED on each of TCP2 and TCP3 (the application of the two REDs being
independent of each other). Here also I am providing priority to UDP2
(without caring if TCP2 or TCP3 is getting starved ).

To schedule between q1 and q2, I am using WRR and to schedule between
UDP1 and TCP1, I am using prio. For implementing q2, I am currently
putting UDP2,TCP2 and TCP3 in 3 different virtual queues and applying
GRED with grio. I am providing UDP2 the highest priority and providing
TCP2 and TCP3 equal priorities. To ensure that RED does not apply on
the UDP2, I have set Tmax=Tmin so that Pbmax=1. But the results I am
getting with this configuration do not match with the results that I
have got from the simulations.

So I want to implement this stuff such that the UDP2 gets highest
priority among the three, is not included while calculating the total
average queue length and the qave used for the application of REDs on
TCP2 and TCP3 should be equal to the qave of tcp2+ qave of tcp3.
To schedule between TCP2 and TCP3, I want to use WRR or something that
gives equal priority and prevents the starvation of any of these.

Regards,
Rahul

-- 
----------------------
"The fear you let build up in your mind is worse than the situation
that actually exists"
from "who moved my cheese"
---------------------------------------------------------------------------------
Rahul Hari
Senior Under Grad. Student,
Department of CSE,
ITBHU,
Varanasi.
Ph: +91-9845347020
rahul.hari@cse06.itbhu.org
------------------------------------------------------------------------------------------

>
>On Mon, 2005-06-06 at 13:39 +0200, Thomas Graf wrote:
>
> > Use a prio qdisc with RED leaf qdiscs. RED and GREDs purpose is to
> > calculate a marking probability and not to provide any prioritizing
> > schemes.
>
>Prioritization is still implicitly provided if you vary the queue
>lengths or the drop probabilities.
>For example, if you set everything to be exactly the same, and varied
>only the drop probability - the VQ with the highest drop probability
>will be less important (i.e relatively more of its packets will be
>dropped; recall: the drop decision is made before the packet is queued).
>
>cheers,
>jamal
>
>
>

Re: [Linux Diffserv] GRED queueing discipline and the filesch_gred.c

[Thomas Graf]

* Rahul Hari <4532f31705060610486ef106a1@mail.gmail.com> 2005-06-06 23:18
> UDP1 and TCP1, I am using prio. For implementing q2, I am currently
> putting UDP2,TCP2 and TCP3 in 3 different virtual queues and applying
> GRED with grio. I am providing UDP2 the highest priority and providing
> TCP2 and TCP3 equal priorities. To ensure that RED does not apply on
> the UDP2, I have set Tmax=Tmin so that Pbmax=1. But the results I am
> getting with this configuration do not match with the results that I
> have got from the simulations.

I assume Tmax being qth_max so you basically disable probability drops
which is the main point of RED. What you do is about equal as a simple
FIFO with hard queue limit comparing against a EWMA based queue length.

Depending on whether you want UDP2 to starve out the others use either
prio or cbq/htb and a GRED in rio mode with equal vq prios for TCP2 and
TCP3. The drops should be roughly proportional to their bandwidth share
but I'm not sure if this is fair enough for you.