[asterisk-users] Help with concurrent VoIP calls

[Darrick Hartman]

John Timms wrote:
> Hi. I'm having trouble figuring out why I'm not able to make many
> concurrent VoIP calls on my system. I'm not aiming for a huge number,
> because I have purposely bought a low powered system, but I would
> think that I could get more. Here are the details:
> 
> I have a small-form-factor Asterisk server with an Intel Atom 230 CPU
> (1.6 GHz, 533 MHz FSB) and 512 MB DDR2 533. It is running Ubuntu
> Server 9.04 with the default Debian package manager installation of
> Asterisk. (version 1.4)

Most of my installations are Soekris net5501's with 512MB ram and a 
500mhz Geode LX processor.  Unless Ubuntu is running a ton of extra junk 
in the background, that processor should be more than adequate.

> Here is what is going on: I'm making outgoing calls (with .call files)
> via SIP (using Vitelity's service, if anyone wants to know) with about
> 55.0 ms latency between my Bellsouth DSL connection & their servers.
> I'm using GSM-format prompts with GSM encoding (disallow=all,
> allow=gsm in sip.conf) and I'm able to make about 7 concurrent calls.
> I have a very fast internet connection, so there is still plenty of
> bandwidth, and the "top" command shows that Asterisk is only at about
> 5% CPU and 10% RAM. Even with only 7 calls, a landline phone will
> "skip" occcasionally, but cell phones have perfect quality.

Your only connection to the PSTN is via SIP right?  Then this is likely 
coincidental that 'landline' calls are different than 'cell phone' 
calls.  The ONLY possibility is that the problem is with your SIP 
termination provider, but even that is unlikely.  As Fred pointed out 
your DSL connection is likely the cause.  Do you have any traffic 
shaping on the network?  If not, you really should have a firewall 
that's capable of prioritizing voice traffic over bulk data traffic. 
What is the actual down and up speed of your DSL connection?

> I don't think that 7 calls is very many, I'll be happy if I can get 10
> good-sounding calls. Can anyone give suggestions? (If this has been
> hashed out elsewhere, I'm happy with a link to more information!)

Use this calculator to see how much bandwidth 10 concurrent calls will take.

http://www.asteriskguru.com/tools/bandwidth_calculator.php

Darrick