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 < [email protected]> 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. > > > > > -- > _____________________________________________________________________ > -- Bandwidth and Colocation Provided by http://www.api-digital.com -- > > asterisk-biz mailing list > To UNSUBSCRIBE or update options visit: > http://lists.digium.com/mailman/listinfo/asterisk-biz >
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