[TriLUG] More Asterisk Qs.. QoS

Reginald Reed reginald.reed at gmail.com
Tue Jun 27 12:46:05 EDT 2006


Any increase in upstream bandwidth should help.  Is the Microwave T1 the
only other option for connectivity?  Also can you set priority higher on
your VoIP traffic over your thermal printer jobs?

On 6/27/06, Brian Henning <brian at strutmasters.com> wrote:
>
> Ok, Jon...
>
> Jon Carnes wrote:
>
> <el snippo>
>
> > Perhaps I'm being ambiguous here. I think its your Pix firewall.
>
> Finally managed to get our VPN/VoIP server outside our PIX (actually,
> just set the VPN/VoIP server to the additional task of gateway and threw
> away the PIX) and quality has increased dramatically.  Round-trip ping
> times now float around 80ms, with occasional spikes to around 250ms, and
> rare worst-case spikes upwards of 450ms.
>
> <snipperoo>
>
> > I've shuttled VoIP traffic across an IPSec VPN using OpenBSD endpoints.
> > It worked fine. I think it would work better with a hardware based
> > solution - but the added latency due to the VPN was minimal. The CPU's
> > seemed to keep up with the traffic stream just fine.
> >
> > Latency spikes across the connection were magnified by the use of the
> > VPN but it was barely noticeable. I think as long as your VPN endpoints
> > can handle the streaming load without buffering then your VoIP should
> > work fine. If there is any significant buffering though the tunnel won't
> > work for Voice.
>
> Looks like nominal VPN latency isn't going to be a problem.  However,
> the spikes do cause momentary blips of course, in the gap between the
> low-lat packet and the following high-lat packet.  The VPN does have to
> occasionally handle traffic bursts, typically in the form of small print
> jobs sent to a thermal UPS label printer in California (and extremely
> rare RDP sessions to the computer hosting said printer).
>
> So, the question is, how do I measure if the tunnel is having to buffer
> much?  Also, how much do you, in your professional opinion, believe we
> would benefit in terms of VoIP performance (with only one remote user,
> generally) by ditching our business-class ADSL (1.5m/384k, I think) for
> a microwave-link T1, assuming we dedicate all 24 channels to data?
>
> Cheers,
> ~Brian
>
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