[cisco-voip] QoS and network guys

[A.L.M.Buxey at lboro.ac.uk]

Hi,

>    Is this a misunderstanding that throwing bandwidth at voice eliminates the
>    need for priorizing voice traffic?  I'm trying to understand why there is

if you have fast ASICs and enough bandwidth there really isnt that much need 
for QoS - and you can check this by performing end to end analysis of jitter
and packet-loss etc - use IPSLA on the links etc to keep an eye on those.

QoS on L2 isnt the same kettle of fish as on a WAN. ont he WAN its quite easy to
define the matrix required in most cases as its 'prioritise voice'. on the L2
there is so much other stuff that the enterprise needs - you're introducing
'unfair queuing' for all the other traffic that ends up in the scavenger and
best efforts queues.... look at the list archives to see many people burnt
by turning QoS on certain line cards and edge switches - ones that just dont have
the buffers (3560 and 2960s i'm looking at you at this point in the conversation)...
you are having to provide buffer metrics - how many packets to handle/clear in each bucket
and unless you know exactly how all the applications/protocols alive on your network
work...well, you'll soon find out ;-)

certainly, there are some networks where they have QoS for more than just voice internally
- they have it for some multicast streams and logistic software and DB connections...

..but there are probably far more people whose network would be better with QoS
turned off totally inside the network. 

(this is the view from a QoS deployer - and I'm still waiting to see caveats lurking
regarding eg wireless APs and their control traffic.....)

alan