[asterisk-biz] Low Bandwidth VoIP

[Stelios Koroneos]

On Mon, 2012-07-16 at 23:08 +0200, Martin Vit wrote:
> 32 channels is doable with g729 annex (dont remember) 6.4 kbit and
> multiplexing.


Annex D is the 6.4kbit (lower bitrate with also a lower voice quality)
As far as i know the Digium g729 asterisk codecs are annex A only
(might have changed since i haven't checked for a while) and all tests
where done using them




> 
> 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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