[c-nsp] QoS Thresholds......

[Saku Ytti]

On (2014-08-18 11:15 -0700), Scott Voll wrote:

Hi Scott,

> If I wanted to change my threshold  number 2, Example:
> 
> *mls qos queue-set output 1 threshold 2 3100 3100 100 3200*
> 
> Would that cause me any issues with Voice quality?

Small catalysts are very demanding platforms on getting QoS ~right, I would
recommend having lab where you can inject 'bad' and 'good' traffic and monitor
result.
One good/cheap way would be to loop TX+RX on one phone, inject radio to
another phone TX and connect RX to speakers, and listen to radio through the
phonecall while labbing QoS, then congest the connections.

But to answer your question, it depends on your output map values and what
value you are planning to change it into. By default all traffic is mapped to
threshold 1, so it wouldn't have any effect.
Thresholds are drop profiles sharing same queue, one application could be to
discriminate two types of best-effort (internal and external?) and give
external best-effort much more aggressive drop-profile (threshold) in BE
queue.

There is one priority queue in 3750 where you might want to put your voice
traffic and set 'priority-queue out' on interface.
Remember also that 3750 is quite sensitive to microbursts so by default just
turning up mls qos you're likely to see poorer quality than without it, there
is good explanation[0] available how actually 'mls qos' can give even BE
better behaviour than without 'mls qos'.

[0] https://supportforums.cisco.com/docs/DOC-8093

-- 
  ++ytti