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

[John Todd]

That's a big can of worms, actually.  You mentioned "Linux" but 
didn't specify if you were talking about network routing or process 
performance; I'll assume network is the topic about which you're 
asking.

The short answer is "VOIP RTP is UDP, which normally pushes TCP 
sessions out of the way, so most of the time everything is OK."

The long answer is that you need to look at QOS (Quality Of Service) 
and how your particular router vendor implements it.  On the "global" 
Internet, you're pretty much out of luck since very few providers 
exchange QOS information to ensure end-to-end priority for packets 
with TOS (Type Of Service) bits set in their headers.  If this is all 
within your own control, you should talk to your router vendor (or 
your router technician) and see what they can tell you about how to 
implement QOS across your network.

Realistically, it's only on congested networks that QOS is 
meaningful, anyway, unless you're doing some freaky 
least-cost-routing tricks with your transit providers (at any layer). 
If your network is at <70% capacity during peak minutes (it is, 
right?) then probably QOS is not going to be necessary.  To give you 
an idea: I regularly use a VPN over a cable modem to connect to a SIP 
gateway 3500 miles and 130ms away, with zero voice artifacts and no 
noticeable quality loss, and this is ALL over the public Internet, 
with no QOS implemented.

In my North American-based experience, QOS is overrated.  There are 
exceptions, but in many cases the problem can be traced to "poor 
network engineering", into which the introduction of QOS will only 
throw things further into a meltdown.

JT


>Just wondering if anyone out there has done any work, or knows where 
>any work is being done, to try to honor the latency requirements of 
>this VOIP stuff and push out SIP and RTP traffic, etc., "ahead of 
>the crowd."
>
>I'm doing my VOIP behind wireless, so it is particularly important. 
>I am getting ready to do some digging, and don't want to re-invent 
>the wheel.
>
>Thx.
>
>B.
>
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