[asterisk-biz] Low Bandwidth VoIP

[Aleks Clark]

You might check out RAD's VMUX-110 units, they compress voice down to 
4kbps/channel, and trunk them together so overhead is minimal. I've used 
them before but can't speak to any hard numbers, voice quality was good 
(this was over satellite), but you'll need T1 hardware to bridge to 
'regular' voip. Spendy gear though. For satellite, you'll spend a lot to 
save a little bit of BW, those MRC's make a lot of weirdness worthwhile :)

On 07/16/2012 02:04 PM, Stelios Koroneos 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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-- 
Aleks Clark
Technical Design Manager
JPI Worldwide Inc.
http://www.jpiworldwide.com
Cell: 1-509-780-3144
Yahoo IM:  jpi_alex
Email:  a.clark at jpiworldwide.com

It is dark. You are likely to be eaten by a grue.

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