On Tue, 2012-07-17 at 05:09 +0100, David Knell 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. > > This is correct if you're using vanilla RTP and no silence suppression. > The G.729 payload runs at 8kbits/sec during talk and 1.6kbits/sec otherwise; > assuming 50% silence gives an average bitrate of 4.8kbits/sec. > Alternatively, > just dropping silent frames brings that down to 4kbits/sec. > > Multiplexing 32 of these over a 250kbits/sec connection should not be a > problem, provided that they're not individually wrapped with RTP, UDP > and IP headers. > > Incidentally, at 50% talk/silence (which is an over-estimate - people listen > more than they talk), the chance of everyone at one end of 32 calls talking > at the same time is 2*10^-10. So there's not going to be many frames > dropped as a result. >
You are also correct in the calculations. The main issue is that the asterisk g729 codec is annex A so there is no silence suppression and thus you get a constant bit rate. http://www1.digium.com/en/products/software/g729-codec If you notice Digium says you can get 140 g729 calls in a T1 (1.5Mbit) using iax trunking, which comes around 10kbit per channel. And this very close to what i have found. After going back and reading my replies, what i should have clarified is that i was talking about *asterisk* getting the 32 channels in 250kbit. g723, or another low bitrate codec might be an option but the voice quality is usually not what the clients expect. -- _____________________________________________________________________ -- 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
