[asterisk-biz] Low Bandwidth VoIP

[Martin Vit]

32 channels is doable with g729 annex (dont remember) 6.4 kbit and
multiplexing.

On Mon, Jul 16, 2012 at 11:04 PM, Stelios Koroneos <
skoroneos at digital-opsis.com> wrote:

> On Mon, 2012-07-16 at 11:11 +0200, Martin Vit wrote:
> >         The short answer is no you can't get 32 *concurrent* channels
> >         on a
> >         250kbps uplink
> >
> >         With G729 as a codec you need around 32kbits per channel
> >         including the
> >         overheads from the voip protocol and tcp etc, so that would
> >         give you
> >         around 7 *concurrent* channels.
> >
> >
> > You are slightly wrong - G729 is 8kbit stream and the UDP overhead for
> > 20ms packetization is alltogether 25Kbit stream. In theory you can do
> > 30 channels over 250 kbit with IAX2 trunking feature which puts all 30
> > channels to one big UDP packet which minimizes headers and UDP
> > overhead. There is also G729 variant using 6.4kbit stream.
> >
>
> The 25kbit is as you said theoretical, the real values i see are close
> to 30kbits for a single channel.
>
> The IAX overhead i have seen during tests is around 20kbits in trunk
> mode and then an additional 9.5 to 10kbits per g729 channel you add to
> the trunk
> So even with that, reaching the 32 channels is not possible and i have
> not accounted the fact they want also VPN.
>
> Had the same issue with a sat link with limited bw so i had to do this
> "exercise" before, that's why i speak with some confidence.
>
> Cisco also offers g729 header compression as they call it which is also
> rated at 24kbit per channel, i assume that there must be other multiplex
> solutions out there, but given the numbers i still believe the 32
> channels on 250kbit is a no-go.
>
>
>
>
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