Voice Quality: G.711 vs G.729

Unanswered Question
Nov 14th, 2008

We are going to be deploying CUCM 6.x for about 100 users. We're considering a SIP ethernet trunk from our carrier (AT&T or PaeTec)

Anybody have any experience with these? How is the reliability?

And more importantly, they offer SIP trunks in G.711 or G.729. You get more concurrent calls per trunk with G.729 obviously, so the cost is less.

But I'm concerned about voice quality. Is the difference noticeable? I want the users (who are new to VoIP) to have a good experience, and clear call quality is very important.


I have this problem too.
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Tim Smith Sat, 11/15/2008 - 04:02

Hi Shane,

Cant help with the SIP trunk provider side.

Probably good idea to have some sort of traditional PSTN backup in this case though.

On the codecs it is really standard practice to use G729 in between branch offices and HQ for example. If the network is configured correctly, I've never had a customer tell me they didnt like the quality.

I have obviously had complaints, when there were QoS misconfigurations or problems on WAN links, but that is not down to the G729 codec.

Main thing to be careful of is the resource requirement.

A couple of things to consider..

1. Make sure you dont compress a G711 music on hold source, it will sound terrible :)

2. IPCC Express - are you using this? It will probably be set to G711 only - so a G729 call will require a Hardware Xcoder to convert.. need to consider how many resources you have available for this..

3. Voicemail - be careful how many G729 calls you throw at it.. by default it will xcode in software, but this will use processor power.. you can use HW resources instead.. so just another design consideration.



shanepresley Mon, 11/17/2008 - 06:27

Thanks Tim, I appreciate the insight.

Regarding Music On Hold, if we provide our own MOH internally, but our provider uses G729, does that mean our callers will get terrible music quality?

And yes, we'll be using IPCC Express. So do we just need a router with DSPs to do the conversion from 711 internally to 729 out the WAN?


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