[asterisk-users] SIP devices with packet loss tolerance

Chris Bagnall lists at minotaur.cc
Mon Apr 23 19:19:49 MST 2007

Thanks for all the replies. Answering the points raised in turn:

> How did you perform the speed tests?

Generally using thinkbroadband.com's speed test java applet.

> On the matter of the BitTorrent factor: did you have the users connect
> the phone, and only the phone, to the Internet connection?

Yep, phone straight into the router, computers etc. all powered down.

> I don't think it's the packet loss per se; it's more likely to be
> jitter, and no, correcting for jitter in Asterisk isn't likely to make
> much difference, because the jitter on upstream connections can be so
> big that it overwhelms the jitter buffer.

The strange thing here is that one some other sites with 2-3 users (remote offices, etc.) where we've deployed "mini-asterisks" (Via Epias in ITX boxes), call quality is much better even over equally "consumer" internet connections. This makes me think that either (or both): 1) IAX is much more tolerant than SIP; 2) Asterisk's jitter buffering is far superior to that in any phones.

> The others responding on-list are certainly giving you good advice. I expect that
> what you are suffering is unmanaged QoS at the roaming users end. This almost
> certainly will be an issue
> with 256k outbound on a network connection that is not dedicated to the voip
> application alone.

I'd hoped that by insisting the users test call quality with their computers turned off that I'd been able to eliminate this factor. You're right of course - if there's heavy net usage going on, call quality will plummet, but it shouldn't be an issue without other net usage, unless I'm mistaken?

>but having a router
> capable of QoS at each location is an absolute necessity. I prefer m0n0wall on a
> Soekris Net4501.

Generally we use a similar setup (though with pfSense) when we're doing small-scale remote offices with 2-4 employees. The net4801/pfSense combo works very well in that environment.

Unfortunately I can't really mandate a mini-asterisk server and Soekris box for each remote user - it'd add many hundreds of pounds to the cost :-)


C.M. Bagnall, Director, Minotaur I.T. Limited
For full contact details visit http://www.minotaur.it/chris.html
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