[c-nsp] qos plan - advice please

[Peter Rathlev]

On Fri, 2013-08-30 at 12:58 -0500, Aaron wrote:
> Why qos?  Does it do any good IF links aren't congested?  In other
> words, if I don't have congestion, is there a reason for it? ...meaning
> that if I can simply add fatter pipes (go from 1 gig to 2 gig
> etherchannel, or from 10 gig to 20 gig etherchannel) then does fatter
> pipe solve all my qos problems? Latency, delay, jitter, bandwidth needs
> solved with fatter pipes?

Since nobody seems to have answered this directly: QoS is regularly used
to lower jitter for some traffic at the expense of other traffic. If you
have so much more capacity than needed that you (practically) never
queue packets you wouldn't need it, but in the area between no queuing
in one end and tail dropping in the other end you have packet reordering
and for example priority queueing.

> In other words, if I have an sla requirement to provide one-way 5 ms
> delay (nothing more or I'm in violation of sla), AND my
> interconnections throughout my network are NOT congested (utilized at
> or above line rate) AND I'm seeing ip sla probes reporting 200 ms
> latency will qos solve this?

If you're seeing 200 ms on a stretch that is normally at 5 ms you either
have wacky measuring equipment or congestion. Where else would the 195
extra ms come from if not from buffering?

-- 
Peter