[TriLUG] More Asterisk Qs.. QoS
brian at strutmasters.com
Tue Jun 20 11:30:25 EDT 2006
Hardware issues aside, I'm having less and less good times with
shoving an Asterisk call over a VPN. Here's what I'm encountering:
When the VPN is established and essentially idle, I get ICMP round-trip
times of about 70 - 80 ms. Not bad.
When a call is in progress, the ping time skyrockets as high as 1250
ms, and never gets much lower than 300 ms. Obviously, the longer the
ping time (assume, for the time being [because I haven't tackled it yet]
there is no QoS throttling taking place), the worse the problems with
echo and garble become.
This testing setup where I'm seeing this behavior is out through our
cable ISP and back in through our DSL ISP. Traceroute conks out at hop
13 in the DSL->Cable direction; I imagine there's a router out there
that is ignoring those packets. Hop 13 is on the right class-C, so I
figure it's only one or two more hops at most to get the rest of the way.
Enabling or disabling lzo compression on the VPN has no effect.
So essentially, my questions become:
1 - Does this sound like just something I can fix with QoS tweaking? I
have to admit embarrassingly that I really have no idea how to start
adjusting QoS in our PIX-501.
2 - Since the VoIP traffic is shuttling across a VPN, the hardware
handling the QoS isn't actually going to know it's VoIP traffic anyway;
all it will see is VPN packets. I haven't scoured the docs too
carefully yet, but does OpenVPN have internal QoS ability? Or is that
something I should do just outside the VPN, such as with tc for example?
I can up the priority of VPN packets themselves, but it won't always
be VoIP traffic within the VPN.
Continued thanks for all the friendly help. :)
Brian A. Henning
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