[Asterisk-Dev] Anyone doing QOS routing on Linux for SIP/RTP?

[Alberto Bertogli]

On Thu, May 15, 2003 at 12:12:38PM -0400, Wade Weppler wrote:
> > The latency is not a problem, as all of the routers (linux boxes) honor
> > the TOS flags, and asterisk sets them correctly.
> 
> My understanding was that simply setting the TOS flags doesn't guarantee
> priority queueing.  QoS uses the tags to set the priorities.  But, as you
> mentioned, voice quality wasn't a problem, so my point is probably moot.

It does by default on Linux routers.

By default, linux sets the queueing discipline to be pfifo_fast, which
pays a lot of attention to TOS bits:

"pfifo_fast is like three tc-pfifo(8) queues side by side, where packets
can be enqueued in  any of  the three bands based on their Type of Service
bits or assigned priority."

This was taken from http://lartc.org/manpages/tc-pfifo_fast.txt.


So you _will_ get priority queueing if you set your TOS right, because the
qdisc will put you under the highest priority queue, and it won't touch
_any_ other queue until this one is empty.


Thanks,
		Alberto