Hi All, For a small installation using ITSPs via DSL is G.729 a worthwhile exercise? I have G.729 capable SIP phones and my ITSPs cupport the codec so I could go end-to-end without transcoding. What's call quality like compared to G.711, GSM or iLBC? Michael -- Michael Graves mgraves@pixelpower.com Sr. Product Specialist www.pixelpower.com Pixel Power Inc. mgraves@mstvp.com o713-861-4005 o800-905-6412 c713-201-1262
asterisk-users-bounces@lists.digium.com wrote:> Hi All, > > For a small installation using ITSPs via DSL is G.729 a > worthwhile exercise? I have G.729 capable SIP phones and my > ITSPs cupport the codec so I could go end-to-end without > transcoding. What's call quality like compared to G.711, GSM or iLBC?Low bandwidth Low CPU utilization Best audio quality Pick any two. G.729 is an extremely low bandwidth codec, offering surprisingly good quality. Unfortunately, it is also a CPU hog. Generally speaking, you should avoid the use of compressed codecs unless bandwidth is a concern. Especially with Asterisk, the performance penalty due to transcoding is a high price to pay. On the LAN, I'm not able to see any reason to use anything but G.711. In the WAN, it depends on how much bandwidth you need for voice, versus what you have available. Keep in mind that the type of trunking you use plays a role. For example, although I haven't done the math, it is entirely possible that 20 trunked channels of IAX2/G.711 would use less bandwidth than 20 discrete SIP/G.729A connections between the same endpoints. Much of the bandwidth used by packetized voice is overhead, so a lower bitrate codec does not yield a linear improvement in bandwidth. There are other considerations as well, such as how well a codec handles a lossy link. This can be very important to the percieved quality of the connection, which, to the user, is far more important. -- No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.0.300 / Virus Database: 265.7.0 - Release Date: 17/01/2005
> Low bandwidth > Low CPU utilization > Best audio quality >I think you might want to clarify that Best audio quality is in relation to other highly compressed codecs. Certainly my (albeit limited) experience is that g711 is much more clear than g729. Compared against gsm, for example, however, the audio quality is quite good.... regards, Paul
There's a MOS scale for this kind of stuff -----Original Message----- From: Paul Fielding [mailto:paul.fielding@shaw.ca] Sent: Wednesday, January 19, 2005 11:24 AM To: Asterisk Users Mailing List - Non-Commercial Discussion Subject: Re: [Asterisk-Users] G.729? Worth it?> Low bandwidth > Low CPU utilization > Best audio quality >I think you might want to clarify that Best audio quality is in relation to other highly compressed codecs. Certainly my (albeit limited) experience is that g711 is much more clear than g729. Compared against gsm, for example, however, the audio quality is quite good.... regards, Paul _______________________________________________ Asterisk-Users mailing list Asterisk-Users@lists.digium.com http://lists.digium.com/mailman/listinfo/asterisk-users To UNSUBSCRIBE or update options visit: http://lists.digium.com/mailman/listinfo/asterisk-users
The MOS (Mean Opinion Score) scale is: 5=Excellent; 4=Good; 3=Fair; 2=Poor; 1=Bad. Some values, taken from "Carrier Grade Voice over IP" by Daniel Collins: G.711 4.3 G.729 4.0 G.729AB 3.9 GSM(full rate) 3.7 The above scores assume no packet loss, minimal delay, no echo. However, IMO such scores are generally only useful for choosing among compression codecs. If you have plenty of bandwidth and minimal packet loss, you should use G.711, not only for better quality, but because it avoids issues with conferencing, DTMF relay, etc. Also, if your ITSP has upstream routes that use a different compression scheme, G.711 avoids cascaded codecs, which sound really awful, MOS < 3 for sure. If you don't have enough bandwidth to handle the desired number of simultaneous calls with G.711, you obviously need to use compression; IMHO G.729 is a good choice. If you have >1% packet loss (or packets effectively lost due to excessive jitter), then G.729 may actually sound better. Lost G.711 samples are replaced with silence, sometimes with pops at the transitions. OTOH, most G.729 implementations have "packet loss concealment", which continues the previous sound, gradually fading out. With 5% loss, a good G.729 system sounds like a mediocre cellular call, but G.711 sounds terrible. There are systems that use G.711 when traffic is light, but switch to compression codecs under heavy traffic to conserve bandwidth. I don't know how/if this can be done in Asterisk. --Stewart