[c-nsp] QoS between 2 routers & many switches

[varaillon]

Yassou,

Before doing anything, I would configure IP SAA on both R1 and R2 in order
to simulate voice traffic and measure jitter, packet loss and delay between
your routers.

This way you could see if what you are doing makes it worst or better for
your voice services.

Christophe

-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Tassos
Chatzithomaoglou
Sent: Tuesday, August 21, 2007 12:15 PM
To: cisco-nsp
Subject: [c-nsp] QoS between 2 routers & many switches

Suppose we have the following network:


     100       100        10       100       100
R1 <===> SW1 <===> SW2 <===> SW3 <===> SW4 <===> R2


All switches are just L2 devices and all connections are just plain
ethernet.
As you can see there is a 10 Mbps link between SW2 and SW3, while all other
links are 100 Mbps.
I need to give priority (& maybe reserve bw) to voice traffic between R1 and
R2.

Does it make sense to try to use QoS (LLQ/CBWFQ) on the routers only? If yes
(that would be the best for me), how can the routers 
"understand" the actual congestion between SW2/SW3, when all intermediate
switches use their own (default ?) buffering/queuing 
mechanisms?
Will there be any difference on the "congestion feedback" that routers get,
if instead of 4 switches, i have 8 switches?

On the other hand:
Should i try to implement QoS on the SW2/SW3 switches only?
Or even better, do i need to implement QoS at both routers & switches?

If the SW2/SW3 connection is EoMPLS, does it make any difference? Do i need
some kind of QoS on the underlying MPLS network too?

-- 
Tassos
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