We are evaluating starting a small VoIP consumer based platform. What is the best codec to use with customers using primarily DSL as internet connectivity? I know that g729 is the king-all, but I want to know what the rest of the professional are using out there. g729 has a cost involved, so does the cost really offset the performance? Or is it better to go with g711 to start off? We plan on using Linksys SPA921 as the primary phone and asterisk open source as the softswitch. Any information you can pass would be appreciated.
On Wed, 6 Jun 2007, Davis Sylvester III wrote:> We are evaluating starting a small VoIP consumer based platform. > What is the best codec to use with customers using primarily DSL as internet > connectivity? > > I know that g729 is the king-all, but I want to know what the rest of > the professional are using out there. g729 has a cost involved, so does > the cost really offset the performance? Or is it better to go with g711 > to start off?It has 2 costs - one the financial one to license it - which you'll need if you need to transcode it for any reason, eg. to connect to your upstream DID provider (or to any sort of local PSTN connection), and the other is the CPU overhead of transcoding... So if you can afford the CPU overhead of transcoding, then off you go! I read an excellent paper off the Xorcom site recently about CPU usage, etc. on a 1GHz CPU. The system managed just over 100 calls using G711, but only just over 20 for GSM, but barely 15 for G729. Scaling with faster CPUs (with bigger caches) is probably better than linear (to a point - see the recent scaling thread!), but it's certainly something worth considering. I'm using G711 for ADSL end-users here in the UK, and I think many others are doing the same. I use G726 as a fall-back (half the bandwidth of G711, and the transcoding cost is very low) in some lower bandwidth situations, or when the client wants to place more calls that can be supported by the upstream of their ADSL line (typically 256 or 488 or 832Kbps, in the UK, depending on the ADSL product they have, the ISP they connect to, and distance from the exchange) I use GSM as a very last resort, or for inter-office trunks where quality isn't as important. If you're the ISP with direct control of the DSL end-points then you'll have the best knowledge of what your punters are doing and line speeds, suitability etc. I've found some ISPs are better at losing UDP packets than others (so I try to migrate my clients off those ISPs and onto good ISPs) Gordon
We use G.729. Consumes only 35kbps of bandwidth and has a level 4 (from 0 to 5) of voice quality. We still have very poor public data networks here in Brazil that makes G.711 a very high bandwith consunption codec for us. Another point that is good for G.729 is that we can bridge calls from customers to SIP-terminators (most/all of them uses g729) without the need to transcode and licence the channels for asterisk (passthrough). Rgds, Ricardo Martins. Davis Sylvester III escreveu:> We are evaluating starting a small VoIP consumer based platform. > What is the best codec to use with customers using primarily DSL as > internet connectivity? > > I know that g729 is the king-all, but I want to know what the rest of > the professional are using out there. g729 has a cost involved, so > does the cost really offset the performance? Or is it better to go > with g711 to start off? > > We plan on using Linksys SPA921 as the primary phone and asterisk open > source as the softswitch. Any information you can pass would be > appreciated. > > _______________________________________________ > --Bandwidth and Colocation provided by Easynews.com -- > > asterisk-users mailing list > To UNSUBSCRIBE or update options visit: > lists.digium.com/mailman/listinfo/asterisk-users >
On 6/7/07, Ricardo Martins <rpoppi77@gmail.com> wrote:> We use G.729. Consumes only 35kbps of bandwidth and has a level 4 (from > 0 to 5) of voice quality. We still have very poor public data networks > here in Brazil that makes G.711 a very high bandwith consunption codec > for us.35kbps sounds very large. We only use 20 kbps untrunked and 13-15 kbps when using IAX trunks. Have you verified this bandwidth usage? -HJC
> I know that g729 is the king-all, but I want to know what the rest of > the professional are using out there. g729 has a cost involved, so does > the cost really offset the performance? Or is it better to go with g711 > to start off?I'm wary of using g711 of public broadband networks. Although theoretically the bandwidth should be there, many consumer ISPs appear to be rather overloaded at certain times of day, so that 256k theoretical (235k real-world) can easily drop to between 100 and 150kbps. Throw in even a small amount of light web browsing and you'll start to get g711 packet loss. g729 is good for speech but very poor for music on hold. I've found speex to be a reasonable compromise - voice quality is similar to g729 (subjectively it's very difficult to tell the difference), but MoH quality is noticeably better. Of course, if your endpoints are SIP hardphones or ATAs you may be forced to use g729 simply because so few hardware devices support speex. It'd be interesting to see some comparisons or comments from people using g726 as this does seem to be supported by quite a few hardware devices. Regards, Chris -- C.M. Bagnall, Director, Minotaur I.T. Limited For full contact details visit minotaur.it/chris.html This email is made from 100% recycled electrons