[afnog] VOIP Traffic shapping

[Paolo Lucente]

Hi Noa,

here are some generic thoughts; i believe more precise considerations
could be done only having knowledge of the underlying infrastructure.
>From what you say, it sounds reasonable to be a QoS issue as VoIP is
sensible to every sort delay, jitter and packet loss. 

* typically service providers care only about quality of their own VoIP
infrastructure. If customers are using anything 3rd party, it should not
really matter you. This is for a number of reasons mainly difficulty in
enforcing reliable trust boundaries and overrall effectiveness of the
solution.

* first step is recognizing VoIP traffic; this involves classification
and marking and is accomplished at the edges of the network. Simplyfing
a little bit, for example, it consists assigning IP precedence x to VoIP
traffic and re-mark data traffic with IP precedence 0.

* second step is prioritizing and guaranteeing bandwidth to the VoIP
class of traffic. Shaping doesn't really apply as it introduces delays
to smooth out traffic peaks to fit into a given rate while containing
as much as possible packet loss.

* prioritization  should follow a strict hop-by-hop behaviour in order
to hit the most effectiveness, in other words, every device on the path
of the VoIP packets has to prioritize them over the other traffic. So,
yes, the ball is in your hands.

I believe pretty all routers/switches vendors have a solution along
these lines; Cisco offers plenty of documentations online for their
kits; i feel to advice LARTC for Linux. 

Worthless to say that the only workaround to QoS is over-provisioning
circuits. Or the other way around, that's purely matter of points of
view and $$$ :-)

A good way to start troubleshooting things could be to get a clue of
how network behaves at various times of the day; monitor latency, 
jitter and packet loss for your POPs and VIP customers from the core
network. Having bandwidth graphs handy will help aswell. Cacti, MRTG
and Smokeping are the tools you might want to look at. Relate figures
with SLAs and complaints (each of which must supply precise times and
dates for the claim) and that should give you a good hint of what's
going on. 

Hope this helps.

Cheers,
Paolo


On Tue, Nov 20, 2007 at 07:28:08AM -0800, Noa of Ark wrote:
> Hi all,
> 
> I am having this problem with some of our clients. We are offering them bandwidth as their service provider and some of them have implemented
>  VOIP  in their home networks and offices.
> 
> Now the link/speed in terms of through put is fine especially with normal browsing, VPN's, Video streaming,downloads etc.
> 
> However, this clients are complaining that,when in comes to Voice traffic,the sound is sometime chappy  (not clear) and  and they cant even make  enough calls.
> 
> I am starting to believe it could be a QoS issue or some sort of congestion on the clients network. I need to help them sort this out since they want to prioritize Voice traffic, but i am not a voip expert. I was thinking of maybe prioritizing VOIP traffic but i am worried about other clients who don't use VOIP services.I am even
> also not sure of how i can implement this.
> 
> Any ideas on how i can troubleshoot this problem, do i need to implement QoS on my Core Routing equipments or something.
> 
> Thanks.
> 
> ----------------
> Maina Noa
> 
>        
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