[LARTC] Info about VoiP Qos

[LARTC] Info about VoiP Qos

[Riccardo Losselli]

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Hi, i've been working on VoIP qos in the few weeks.
I shape IAX2 and SIP, and i'm getting some interesting results.
Im using HTB, the line is 512Kbps dedicated line, and we have some
servers on the same line that generate quite a lot of traffic,
frequently saturating the link.
I've read through LARTC how to, example, etc, and so far i'm at this point:

I can can shape the servers traffic, based on ip and services
I can shape the Voip traffic
If i reserve some bandwith for VoIP and the rest for server traffic, it
all runs smooth
This setup works by creating a root disc, then two "source" disc, one
rated at 100 Kbps for voip, one rated 300Kbps. The remaining 100Kbps is
"wasted" to avoid buffering from the router

But i would like to have the possibility to use all the 400Kbps and slow
down server traffic only when and if needed.

I prioritized VoIP traffic, using the various scripts around, and what i
get is that, even if voip quality is definitely much much better than
without shaping, there are is still statics and pops, and some
interruption of the voice and only if i'm called from POTS
I do not get this when completely reserving the bandwith or when the
link is not loaded.

i would like to ask if this is a normal behaviour before keeping to try
to understand if i missed something somewhere..
if it's not normal i would post my script and ask for a suggestion.
BTW i get the same results when using wondershaper and so on.

Thanks,
Ricky
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Re: [LARTC] Info about VoiP Qos

[Jason Boxman]

On Saturday 22 January 2005 12:15, Riccardo Losselli wrote:
<snip>
> i would like to ask if this is a normal behaviour before keeping to try
> to understand if i missed something somewhere..
> if it's not normal i would post my script and ask for a suggestion.
> BTW i get the same results when using wondershaper and so on.

What I found most helpful, when things were not working as I thought I had 
configured them to, was to graph for a duration and compare the incidents 
with the graph output.  If you can pinpoint spikes on the graph or other 
events with VoIP issues, you might see if your configuration is at fault.

( Shameless plug:
http://trekweb.com/~jasonb/articles/traffic_shaping/monitoring.html )

-- 

Jason Boxman
Perl Programmer / *NIX Systems Administrator
Shimberg Center for Affordable Housing | University of Florida
http://edseek.com/ - Linux and FOSS stuff

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Re: [LARTC] Info about VoiP Qos

[Riccardo Losselli]

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| What I found most helpful, when things were not working as I thought I
had
| configured them to, was to graph for a duration and compare the incidents
| with the graph output.  If you can pinpoint spikes on the graph or other
| events with VoIP issues, you might see if your configuration is at fault.
|
| ( Shameless plug:
| http://trekweb.com/~jasonb/articles/traffic_shaping/monitoring.html )

Thanks.. it will be useful!

I've just graphed it, and it seems ok.. i can see the root, the four
child (three are used to shape each one of the three lines we have, that
share the same shaper, one is used to put the traffic going from one of
the three local nets to the other, which i do not want to be shaped)
and their respective child, and finally the leaf classes (question: is
it necessary to attach a leaf sfq or pfifo class to make things work? i
guess no, it's just used to give fairness to each connections sent to
the class, right?)
I can also se the filters that use "mark" policy go directly to the root
class. I did not understand exactly why filters are attached to the root
qdisc, and not to the qdisc they refer too, but i guess it's a correct
behavious as i see it in every script around...
i'll try to see if i can understand alittle more with the traffic graphs
too..
Thanks again,
Ricky
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Re: [LARTC] Info about VoiP Qos

[Riccardo Losselli]

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Thanks again to Jason..
i plotted the classes and they are as i wished them to be..
I also plotted the traffic, while heavily using the link.
I gave Voip a 100Kbit rate (it need between 80 and 90some) and it worked.
There are no visibile spikes (traffic si not exactly flat, but
variations are minimal) and stay betwen 80Kbps and 90some.
So it should be fine.. traffic is prioritarized, prio 1, while the other
traffic is 3 or more..
Leaf classes are sfq perturb 10
I still hear the pops..
If it can be a useful hint, the problem appears only when i'm called,
not when i call (i use two diffent servers when making calls and receiving).
The only one who hears the pops i the one on the POTS phone that is
calling me, i do not hear any pop (but i guess it's because my link is
saturated upstream only)
At first i thought that it was a problem of the server used to call me.
but if I the almost zero the non voip traffic the pops disappear...
Will test more...

Bye,
Ricky
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Re: [LARTC] Info about VoiP Qos

[Ed Wildgoose]

> But i would like to have the possibility to use all the 400Kbps and slow
> down server traffic only when and if needed.
>
> I prioritized VoIP traffic, using the various scripts around, and what i
> get is that, even if voip quality is definitely much much better than
> without shaping, there are is still statics and pops, and some
> interruption of the voice and only if i'm called from POTS
> I do not get this when completely reserving the bandwith or when the
> link is not loaded.


You probably forgot to tweak the HTB code to change the hysterisis value?

This helps a lot with the output stuff.  However, remember that you 
always have to slow down the incoming to a little less than max 
otherwise by the time the stuff is throttled you see some small amount 
of queuing at the remote end.

Also remember that the bandwidth of most adsl links is less than the 
stated bandwidth.  This is because of ATM overheads (which vary 
depending on packet size) and also because the link is contended.

Put this all together and you should be able to get pretty close to 
maximum,. perhaps only reserving a small amount of bandwidth and make 
the rest shareable.

Good luck

Ed W
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Re: [LARTC] Info about VoiP Qos

[Riccardo Losselli]

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Ed Wildgoose wrote:
| Please reply onlist in general
|

Sorry, i didn't notice the answer went to you only.. i did the same
mistake with Jason.

| Check the HTB code in iproute and look for the "hysteris" variable.
| Basically it just lets a couple of packets burst out at the same time
| instead of doinga  very granular per packet throttling.

ok..

| Find out what the protocol is on the line.  ADSL for example uses ATM to
| encapsulate each packet.  YOu buy 512Kbs of ATM bandwidth, which
| actually works out as somewhat less TCP bandwidth (which is what you are
| throttling).  So do some speed tests on the line and work out the REAL
| speed of the line.  Preferably use small packets since the overhead of
| encapsulation often shoots up then.
|
| This might not be relevant though - just a warning though

I understand it's a frame relay


| I meant, reserve (say) 10Kbs, and only share the rest...

I see.. this way it works.
Things are getting a little more complicated though..
I tested with some people, calling ip to ip, and it works just fine.
I understand that, if it's just a matter of my bandwith being overloaded
and not correctly shaped i should get the same disturbs, but i do not.
I suspect there is something involved on the server that converts the
call from ip to POTS and vice versa too..

Thanks!
Ricky
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