g.711 vs g.729a

**ctaranto** · 02-11-2010 08:03 AM

I didn't want to bother support with this question (as my service is working fine).

I recently received a PAP2T as a replacement for a (defective) RT31P2. I also had a PAP2T with my previous VoIP provider (VoicePulse). The RT's web interface is very bland compared to the wealth of information the PAP2T provides. That said, I don't know what the RT uses...

The PAP2T with VOIPo is using the g.729a compression codec. My previous provider was using the g.711a codec (again, using the same kind of ATA). I did a little research this morning on the differences. The 729 is newer, but does a lot more compression, and is quite a complex algorithm, mixing synthesized data and the actual voice data. The 711 is the traditional codec which does very little compression and passes along the actual voice.

The 729 uses only 8kbps of upstream bandwidth. The 711, on the other hand, uses 64kbps of upstream bandwidth.

Logic says that the 711 will sound better since there's less compression, and it's sending along the voice without much fuss. But on a call with my wife this morning, I really couldn't determine a difference. Granted at home we have cordless phone, and the phones at my work are also VoIP. Bandwidth for me isn't a big deal (Comcast 12/2 service).

I'm curious if anyone has opinions on the quality of 711 vs 729, issues with 729 regarding faxing, DTMF, etc. Is there a way to switch to 711 if one wanted to (this is more for VOIPo support that others here)?

Update:
I found this useful link: Voice Over IP - Per Connection Bandwidth. Actual usage of 711 is ~87kbps, 729 is ~31kbps.

Thanks,

-Craig

**burris** · 02-11-2010 09:22 AM

In your VOIPo PAP2, where do you see that they use 729..?

I see 711 as the preferred codec on mine and at the moment, mine is and has been provisioned.

**usa2k** · 02-11-2010 09:35 AM

Tim has always said their standard is G.711
A low bandwidth option would be a great feature.
If made available, the codec could be added to the Device display page.

Many HSI services are fast enough for G.711 and will sound better if experiencing packet loss, due to smaller portions of voice in each packet sample. If a few packets get lost they are less noticeable. Also, if a customer is determined enough to try conventional FAX, G.711 will be more successful if successful at all.

Back in 2003 when I first used Vonage, many people needed a small bandwidth codec. A soft phone today, might benefit from using G.726 due to variable access providers they could tie into.

Vonage in 2003 used:

G.723 Low Bandwidth
G.726 Medium Bandwidth
G.711 High Bandwidth and FAX mode.

TRIVIA: The Cisco ATA 286 could only handle one high compression conversation at a time due to the processing power of the ATA even though the device could provide two separate lines.

**ctaranto** · 02-11-2010 10:02 AM

Originally Posted by burris

In your VOIPo PAP2, where do you see that they use 729..?

I see 711 as the preferred codec on mine and at the moment, mine is and has been provisioned.

On the main "Info" screen of the web interface, there is:
Call 1 Encoder:
Call 1 Decoder:

Both said G729a when she called me this morning.

Where do you see "preferred codec"?

-Craig

**burris** · 02-11-2010 10:12 AM

Depends whether you have admin access to your ATA. If you got the ATA from VOIPo, I don't think you will have access.

If you do, go to the line tabs and scroll down.

**burris** · 02-11-2010 10:16 AM

Originally Posted by ctaranto

On the main "Info" screen of the web interface, there is:
Call 1 Encoder:
Call 1 Decoder:

Both said G729a when she called me this morning.

Where do you see "preferred codec"?

-Craig

Thinking some, maybe what you are seeing is the codec that the caller's service is using, since that info may be only for inbound..

**ctaranto** · 02-11-2010 10:24 AM

Originally Posted by burris

Thinking some, maybe what you are seeing is the codec that the caller's service is using, since that info may be only for inbound..

Don't think so, because with my previous provider, calls to the same work phone would show G711a.

I don't have admin access to my adapter (VOIPo provided). I'll file a support ticket to see what's up and if I can be changed to G711.

Thanks,

-Craig

**ctaranto** · 02-11-2010 10:54 AM

VOIPo support confirmed that G711 is the default and is used in 99% of the calls. I'll be keeping an eye on it to see if I can get a sense of the % of G711 and G729.

Maybe just a freak chance that the one time I checked (the new adapter), it was G729?

-Craig

**ctaranto** · 02-12-2010 07:46 AM

I've been looking at calls and all since the above post have been G711u. My wife called me this morning (same scenario where G729a was used above), and it also was G711u.

I'm interested in what causes the flip to G729a (just curious).

-Craig

**VOIPoBrandon** · 02-12-2010 09:45 AM

Originally Posted by ctaranto

I've been looking at calls and all since the above post have been G711u. My wife called me this morning (same scenario where G729a was used above), and it also was G711u.

I'm interested in what causes the flip to G729a (just curious).

-Craig

It just depends on what codec is being established with the upstream carrier, the VOIPo device is relaying that it can handle G711 and G729. We do this as a higher number of your international calls will be G729, so without it more international calls would fail in some scenarios. Other than this most of your domestic calling will be negotiated at G711. However again it depends on who or where the call is going.